diff --git a/lib/brave_search.ex b/lib/brave_search.ex
index 63db9316..d8bea0c7 100644
--- a/lib/brave_search.ex
+++ b/lib/brave_search.ex
@@ -1,10 +1,12 @@
 defmodule BraveSearch do
   alias BraveSearch.API
 
+  @spec search_images(String.t(), keyword()) :: {:ok, [map()]} | {:error, term()}
   def search_images(query, opts \\ []) do
     API.search_images(query, opts, config())
   end
 
+  @spec download_image(String.t()) :: {:ok, binary()} | {:error, :download_failed}
   def download_image(url) do
     API.download_image(url, config())
   end
diff --git a/lib/brave_search/api.ex b/lib/brave_search/api.ex
index d0362774..559018a5 100644
--- a/lib/brave_search/api.ex
+++ b/lib/brave_search/api.ex
@@ -5,6 +5,8 @@ defmodule BraveSearch.API do
 
   require Logger
 
+  @spec search_images(String.t(), keyword(), BraveSearch.Config.t()) ::
+          {:ok, [map()]} | {:error, term()}
   def search_images(query, opts, config) do
     params = [q: query, count: Keyword.get(opts, :count, 20)]
 
@@ -34,6 +36,8 @@ defmodule BraveSearch.API do
     end
   end
 
+  @spec download_image(String.t(), BraveSearch.Config.t()) ::
+          {:ok, binary()} | {:error, :download_failed}
   def download_image(url, config) do
     case Req.new(url: url, max_retries: 1, user_agent: config.user_agent)
          |> Req.Request.merge_options(config.req_options)
diff --git a/lib/discogs.ex b/lib/discogs.ex
index 4dc1c874..03c3b9ba 100644
--- a/lib/discogs.ex
+++ b/lib/discogs.ex
@@ -1,12 +1,14 @@
 defmodule Discogs do
   alias Discogs.API
 
+  @spec get_artist(integer() | String.t()) :: {:ok, map()} | {:error, term()}
   def get_artist(id) do
     discogs_config = discogs_config()
 
     API.get_artist(id, discogs_config)
   end
 
+  @spec get_artist_image(String.t()) :: {:ok, binary()} | {:error, :cover_not_available}
   def get_artist_image(url) do
     discogs_config = discogs_config()
 
diff --git a/lib/discogs/api.ex b/lib/discogs/api.ex
index 93a89b88..7a897d2e 100644
--- a/lib/discogs/api.ex
+++ b/lib/discogs/api.ex
@@ -5,6 +5,7 @@ defmodule Discogs.API do
 
   require Logger
 
+  @spec get_artist(integer() | String.t(), Discogs.Config.t()) :: {:ok, map()} | {:error, term()}
   def get_artist(id, config) do
     config
     |> new_request()
@@ -15,6 +16,8 @@ defmodule Discogs.API do
     |> get_request()
   end
 
+  @spec get_artist_image(String.t(), Discogs.Config.t()) ::
+          {:ok, binary()} | {:error, :cover_not_available}
   def get_artist_image(url, config) do
     case Req.new(url: url, max_retries: 1, user_agent: config.user_agent)
          |> Req.Request.merge_options(config.req_options)
diff --git a/lib/last_fm.ex b/lib/last_fm.ex
index a76780f2..8ec9bb1c 100644
--- a/lib/last_fm.ex
+++ b/lib/last_fm.ex
@@ -2,19 +2,24 @@ defmodule LastFm do
   alias LastFm.{API, Feed, Refresh, Scrobble, Track, Worker}
   alias MusicLibrary.{BackgroundRepo, Repo}
 
+  @spec subscribe_to_feed() :: :ok
   def subscribe_to_feed, do: Feed.subscribe()
 
+  @spec refresh_scrobbled_tracks() :: :ok | {:error, term()}
   def refresh_scrobbled_tracks, do: Refresh.refresh()
 
+  @spec get_tracks(keyword()) :: {:ok, [Track.t()]} | {:error, term()}
   def get_tracks(opts) do
     last_fm_config = last_fm_config()
     API.get_recent_tracks(opts, last_fm_config)
   end
 
+  @spec lowest_scrobbled_at_uts() :: integer() | nil
   def lowest_scrobbled_at_uts do
     Repo.aggregate(Track, :min, :scrobbled_at_uts)
   end
 
+  @spec backfill_scrobbled_tracks() :: {:ok, Oban.Job.t()} | {:error, Ecto.Changeset.t()}
   def backfill_scrobbled_tracks do
     to_uts = lowest_scrobbled_at_uts()
 
@@ -23,6 +28,7 @@ defmodule LastFm do
     |> BackgroundRepo.insert()
   end
 
+  @spec get_artist_info(String.t(), String.t()) :: {:ok, LastFm.Artist.t()} | {:error, term()}
   def get_artist_info(musicbrainz_id, name) do
     last_fm_config = last_fm_config()
 
@@ -40,6 +46,8 @@ defmodule LastFm do
     end
   end
 
+  @spec get_similar_artists(String.t(), String.t()) ::
+          {:ok, [LastFm.Artist.t()]} | {:error, term()}
   def get_similar_artists(musicbrainz_id, name) do
     last_fm_config = last_fm_config()
 
@@ -57,6 +65,8 @@ defmodule LastFm do
     end
   end
 
+  @spec get_artist_tags(String.t(), String.t()) ::
+          {:ok, [{String.t(), integer()}]} | {:error, term()}
   def get_artist_tags(musicbrainz_id, name) do
     last_fm_config = last_fm_config()
 
@@ -74,12 +84,14 @@ defmodule LastFm do
     end
   end
 
+  @spec get_session(String.t()) :: {:ok, LastFm.Session.t()} | {:error, term()}
   def get_session(token) do
     last_fm_config = last_fm_config()
 
     API.get_session(token, last_fm_config)
   end
 
+  @spec scrobble([Scrobble.t()], String.t()) :: {:ok, map()} | {:error, term()}
   def scrobble(scrobbles, session_key) do
     last_fm_config = last_fm_config()
 
@@ -88,6 +100,7 @@ defmodule LastFm do
     |> API.scrobble(session_key, last_fm_config)
   end
 
+  @spec auth_url() :: String.t()
   def auth_url do
     last_fm_config = last_fm_config()
     "https://www.last.fm/api/auth/?api_key=" <> last_fm_config.api_key
diff --git a/lib/last_fm/album.ex b/lib/last_fm/album.ex
index 51f17e30..42aabeab 100644
--- a/lib/last_fm/album.ex
+++ b/lib/last_fm/album.ex
@@ -13,6 +13,7 @@ defmodule LastFm.Album do
     field :title, :string
   end
 
+  @spec changeset(t(), map()) :: Ecto.Changeset.t()
   def changeset(album, attrs) do
     album
     |> cast(attrs, [:musicbrainz_id, :title])
diff --git a/lib/last_fm/api.ex b/lib/last_fm/api.ex
index f5f1196e..4622833d 100644
--- a/lib/last_fm/api.ex
+++ b/lib/last_fm/api.ex
@@ -4,6 +4,9 @@ defmodule LastFm.API do
 
   require Logger
 
+  @type id_or_name :: {:musicbrainz_id, String.t()} | {:name, String.t()}
+
+  @spec get_session(String.t(), LastFm.Config.t()) :: {:ok, Session.t()} | {:error, term()}
   def get_session(token, config) do
     params =
       %{
@@ -24,6 +27,7 @@ defmodule LastFm.API do
     |> get_request()
   end
 
+  @spec scrobble([map()], String.t(), LastFm.Config.t()) :: {:ok, map()} | {:error, term()}
   def scrobble(tracks, session_key, config) do
     params =
       %{"api_key" => config.api_key, "method" => "track.scrobble", "sk" => session_key}
@@ -51,6 +55,7 @@ defmodule LastFm.API do
     |> post_request()
   end
 
+  @spec get_recent_tracks(keyword(), LastFm.Config.t()) :: {:ok, [Track.t()]} | {:error, term()}
   def get_recent_tracks(opts \\ [], config) do
     to_uts = Keyword.get(opts, :to_uts)
     limit = Keyword.get(opts, :limit, 100)
@@ -69,6 +74,7 @@ defmodule LastFm.API do
     |> get_request()
   end
 
+  @spec get_artist_info(id_or_name(), LastFm.Config.t()) :: {:ok, Artist.t()} | {:error, term()}
   def get_artist_info(id_or_name_option, config) do
     params =
       config
@@ -83,6 +89,8 @@ defmodule LastFm.API do
     |> get_request()
   end
 
+  @spec get_similar_artists(id_or_name(), LastFm.Config.t()) ::
+          {:ok, [Artist.t()]} | {:error, term()}
   def get_similar_artists(id_or_name_option, config) do
     params =
       config
@@ -97,6 +105,8 @@ defmodule LastFm.API do
     |> get_request()
   end
 
+  @spec get_artist_tags(id_or_name(), LastFm.Config.t()) ::
+          {:ok, [{String.t(), integer()}]} | {:error, term()}
   def get_artist_tags(id_or_name_option, config) do
     params =
       config
diff --git a/lib/last_fm/api/error_response.ex b/lib/last_fm/api/error_response.ex
index 52c61c12..dd151037 100644
--- a/lib/last_fm/api/error_response.ex
+++ b/lib/last_fm/api/error_response.ex
@@ -1,6 +1,28 @@
 defmodule LastFm.API.ErrorResponse do
   defstruct [:error, :message]
 
+  @type error_atom ::
+          :invalid_service
+          | :invalid_method
+          | :authentication_failed
+          | :invalid_format
+          | :invalid_parameters
+          | :invalid_resource
+          | :operation_failed
+          | :invalid_session_key
+          | :invalid_api_key
+          | :service_offline
+          | :invalid_method_signature
+          | :transient_error
+          | :suspended_api_key
+          | :rate_limit_exceeded
+
+  @type t :: %__MODULE__{
+          error: error_atom(),
+          message: String.t()
+        }
+
+  @spec new(integer(), String.t()) :: t()
   def new(error_code, message) do
     %__MODULE__{error: map_error(error_code), message: message}
   end
@@ -23,6 +45,7 @@ defmodule LastFm.API.ErrorResponse do
   @doc """
   Returns true if the error is retryable, false otherwise.
   """
+  @spec retryable_error?(atom()) :: boolean()
   def retryable_error?(error)
       when error in [:transient_error, :service_offline, :rate_limit_exceeded, :operation_failed],
       do: true
@@ -33,6 +56,7 @@ defmodule LastFm.API.ErrorResponse do
   Returns the recommended retry delay in milliseconds for retryable errors.
   Returns nil for non-retryable errors.
   """
+  @spec retry_delay(atom()) :: pos_integer() | nil
   # 1 minute
   def retry_delay(:rate_limit_exceeded), do: 60_000
   # 30 seconds
diff --git a/lib/last_fm/api/signature.ex b/lib/last_fm/api/signature.ex
index b82ca4f1..b18fabf8 100644
--- a/lib/last_fm/api/signature.ex
+++ b/lib/last_fm/api/signature.ex
@@ -1,4 +1,5 @@
 defmodule LastFm.API.Signature do
+  @spec generate(map() | keyword(), String.t()) :: String.t()
   def generate(params, shared_secret) do
     encoded_params =
       params
diff --git a/lib/last_fm/artist.ex b/lib/last_fm/artist.ex
index c525c842..d8f7c83f 100644
--- a/lib/last_fm/artist.ex
+++ b/lib/last_fm/artist.ex
@@ -28,6 +28,7 @@ defmodule LastFm.Artist do
     field :image_data_hash, :string
   end
 
+  @spec from_api_response(map()) :: t()
   def from_api_response(api_response) do
     %__MODULE__{
       musicbrainz_id: api_response["mbid"],
@@ -41,6 +42,7 @@ defmodule LastFm.Artist do
     }
   end
 
+  @spec changeset(t(), map()) :: Ecto.Changeset.t()
   def changeset(artist, attrs) do
     artist
     |> cast(attrs, [
@@ -56,6 +58,7 @@ defmodule LastFm.Artist do
     |> validate_required([:name])
   end
 
+  @spec events_url(t()) :: String.t()
   def events_url(artist) do
     artist.base_url <> "/+events"
   end
diff --git a/lib/last_fm/import.ex b/lib/last_fm/import.ex
index e0747c6b..66514fb8 100644
--- a/lib/last_fm/import.ex
+++ b/lib/last_fm/import.ex
@@ -1,4 +1,5 @@
 defmodule LastFm.Import do
+  @spec batch(keyword()) :: {:ok, non_neg_integer()} | {:error, term()}
   def batch(opts) do
     with {:ok, tracks} <- LastFm.get_tracks(opts) do
       LastFm.Feed.update(tracks)
diff --git a/lib/last_fm/scrobble.ex b/lib/last_fm/scrobble.ex
index ff2b16ff..9b9804b9 100644
--- a/lib/last_fm/scrobble.ex
+++ b/lib/last_fm/scrobble.ex
@@ -1,6 +1,16 @@
 defmodule LastFm.Scrobble do
   defstruct [:track, :artist, :timestamp, :album, :album_artist, :mbid]
 
+  @type t :: %__MODULE__{
+          track: String.t(),
+          artist: String.t(),
+          timestamp: integer(),
+          album: String.t() | nil,
+          album_artist: String.t() | nil,
+          mbid: String.t() | nil
+        }
+
+  @spec encode(t()) :: map()
   def encode(scrobble) do
     scrobble
     |> Map.from_struct()
diff --git a/lib/last_fm/session.ex b/lib/last_fm/session.ex
index 4edcc3b4..60244e06 100644
--- a/lib/last_fm/session.ex
+++ b/lib/last_fm/session.ex
@@ -3,6 +3,12 @@ defmodule LastFm.Session do
 
   defstruct [:name, :key, :pro]
 
+  @type t :: %__MODULE__{
+          name: String.t() | nil,
+          key: String.t() | nil,
+          pro: boolean() | nil
+        }
+
   Record.defrecord(
     :xmlAttribute,
     Record.extract(:xmlAttribute, from_lib: "xmerl/include/xmerl.hrl")
@@ -32,6 +38,7 @@ defmodule LastFm.Session do
         pro: true
       }
   """
+  @spec parse(String.t()) :: t()
   def parse(xml_string) do
     doc = scan(xml_string)
 
@@ -77,6 +84,7 @@ defmodule LastFm.Session do
     :xmerl_xpath.string(to_charlist(path), node)
   end
 
+  @spec text(tuple() | nil) :: String.t() | nil
   def text(node), do: node |> xpath(~c"./text()") |> extract_text()
 
   defp extract_text([xmlText(value: value)]), do: List.to_string(value)
diff --git a/lib/last_fm/track.ex b/lib/last_fm/track.ex
index 007109f9..016e6292 100644
--- a/lib/last_fm/track.ex
+++ b/lib/last_fm/track.ex
@@ -35,6 +35,7 @@ defmodule LastFm.Track do
     field :last_fm_data, :map, default: %{}
   end
 
+  @spec from_api_response([map()]) :: [t()]
   def from_api_response(raw_tracks) do
     raw_tracks
     |> Enum.reject(&now_playing?/1)
@@ -79,6 +80,7 @@ defmodule LastFm.Track do
     end
   end
 
+  @spec changeset(t(), map()) :: Ecto.Changeset.t()
   def changeset(track, attrs) do
     track
     |> cast(attrs, [
diff --git a/lib/mix/tasks/esbuild/check_version.ex b/lib/mix/tasks/esbuild/check_version.ex
index 919615d7..6b7f027c 100644
--- a/lib/mix/tasks/esbuild/check_version.ex
+++ b/lib/mix/tasks/esbuild/check_version.ex
@@ -1,7 +1,7 @@
 defmodule Mix.Tasks.Esbuild.CheckVersion do
-  @shortdoc "Checks the the current Esbuild version is the latest"
+  @shortdoc "Checks the current Esbuild version is the latest"
   @moduledoc """
-  Checks the the current esbuild version is the latest.
+  Checks the current esbuild version is the latest.
 
   Exits with 0 if versions match, 1 if the esbuild needs to be updated.
   """
diff --git a/lib/music_brainz.ex b/lib/music_brainz.ex
index ee6c8eec..4d96851e 100644
--- a/lib/music_brainz.ex
+++ b/lib/music_brainz.ex
@@ -1,6 +1,15 @@
 defmodule MusicBrainz do
   alias MusicBrainz.API
 
+  @type search_opts :: [limit: non_neg_integer(), offset: non_neg_integer()]
+
+  @spec search_release_group(String.t(), search_opts()) ::
+          {:ok,
+           %{
+             total_count: non_neg_integer(),
+             release_groups: [MusicBrainz.ReleaseGroupSearchResult.t()]
+           }}
+          | {:error, term()}
   def search_release_group(query, opts \\ []) do
     limit = Keyword.get(opts, :limit, 20)
     offset = Keyword.get(opts, :offset, 0)
@@ -12,26 +21,34 @@ defmodule MusicBrainz do
     )
   end
 
+  @spec get_release_group(String.t()) :: {:ok, map()} | {:error, term()}
   def get_release_group(musicbrainz_id) do
     API.get_release_group(musicbrainz_id, music_brainz_config())
   end
 
+  @spec get_releases(String.t(), keyword()) :: {:ok, map()} | {:error, term()}
   def get_releases(musicbrainz_id, opts) do
     API.get_releases(musicbrainz_id, opts, music_brainz_config())
   end
 
+  @spec get_release(String.t()) :: {:ok, map()} | {:error, term()}
   def get_release(musicbrainz_id) do
     API.get_release(musicbrainz_id, music_brainz_config())
   end
 
+  @spec search_release_by_barcode(String.t()) ::
+          {:ok, [MusicBrainz.ReleaseSearchResult.t()]} | {:error, term()}
   def search_release_by_barcode(barcode) do
     API.search_release_by_barcode(barcode, music_brainz_config())
   end
 
+  @spec get_cover_art({:musicbrainz_id, String.t()} | {:url, String.t()}) ::
+          {:ok, binary()} | {:error, term()}
   def get_cover_art(id_or_url) do
     API.get_cover_art(id_or_url, music_brainz_config())
   end
 
+  @spec get_artist(String.t()) :: {:ok, MusicBrainz.Artist.t()} | {:error, term()}
   def get_artist(musicbrainz_id) do
     API.get_artist(musicbrainz_id, music_brainz_config())
   end
diff --git a/lib/music_brainz/api.ex b/lib/music_brainz/api.ex
index 70fdcf7e..21ab3128 100644
--- a/lib/music_brainz/api.ex
+++ b/lib/music_brainz/api.ex
@@ -206,6 +206,7 @@ defmodule MusicBrainz.API do
         }
   """
 
+  @spec get_release_group(String.t(), MusicBrainz.Config.t()) :: {:ok, map()} | {:error, term()}
   def get_release_group(id, config) do
     config
     |> new_request()
@@ -282,6 +283,7 @@ defmodule MusicBrainz.API do
         "title": "Clark (Soundtrack From the Netflix Series)"
       }
   """
+  @spec get_release(String.t(), MusicBrainz.Config.t()) :: {:ok, map()} | {:error, term()}
   def get_release(id, config) do
     config
     |> new_request()
@@ -295,6 +297,8 @@ defmodule MusicBrainz.API do
     |> get_request()
   end
 
+  @spec get_releases(String.t(), keyword(), MusicBrainz.Config.t()) ::
+          {:ok, map()} | {:error, term()}
   def get_releases(release_group_id, opts, config) do
     Keyword.validate!(opts, [:limit, :offset])
 
@@ -314,6 +318,8 @@ defmodule MusicBrainz.API do
     |> get_request()
   end
 
+  @spec search_release_by_barcode(String.t(), MusicBrainz.Config.t()) ::
+          {:ok, [ReleaseSearchResult.t()]} | {:error, term()}
   def search_release_by_barcode(barcode, config) do
     config
     |> new_request()
@@ -430,6 +436,9 @@ defmodule MusicBrainz.API do
         ]
       }
   """
+  @spec search_release_group(String.t(), keyword(), MusicBrainz.Config.t()) ::
+          {:ok, %{total_count: non_neg_integer(), release_groups: [ReleaseGroupSearchResult.t()]}}
+          | {:error, term()}
   def search_release_group(query, opts, config) do
     Keyword.validate!(opts, [:limit, :offset])
 
@@ -451,6 +460,7 @@ defmodule MusicBrainz.API do
     |> get_request()
   end
 
+  @spec get_artist(String.t(), MusicBrainz.Config.t()) :: {:ok, Artist.t()} | {:error, term()}
   def get_artist(musicbrainz_id, config) do
     config
     |> new_request()
@@ -468,6 +478,8 @@ defmodule MusicBrainz.API do
   @doc """
   Uses the [cover art](https://musicbrainz.org/doc/Cover_Art_Archive/API) endpoint with the release group id to get the cover image.
   """
+  @spec get_cover_art({:musicbrainz_id, String.t()} | {:url, String.t()}, MusicBrainz.Config.t()) ::
+          {:ok, binary()} | {:error, :cover_not_available}
   def get_cover_art({:musicbrainz_id, musicbrainz_id}, config) do
     url = "https://coverartarchive.org/release-group/#{musicbrainz_id}/front"
 
diff --git a/lib/music_brainz/artist.ex b/lib/music_brainz/artist.ex
index 859f79bb..cbbbb576 100644
--- a/lib/music_brainz/artist.ex
+++ b/lib/music_brainz/artist.ex
@@ -2,6 +2,16 @@ defmodule MusicBrainz.Artist do
   @enforce_keys [:id, :name, :sort_name]
   defstruct [:id, :name, :sort_name, :country, :relations, :musicbrainz_data]
 
+  @type t :: %__MODULE__{
+          id: String.t(),
+          name: String.t(),
+          sort_name: String.t(),
+          country: String.t() | nil,
+          relations: [map()] | nil,
+          musicbrainz_data: map() | nil
+        }
+
+  @spec from_api_response(map()) :: t()
   def from_api_response(r) do
     %__MODULE__{
       id: r["id"],
@@ -15,6 +25,7 @@ defmodule MusicBrainz.Artist do
 
   # MASSIVE ASSUMPTION: if there's more than one Discogs link,
   # take the one with the lowest ID, as it's likely to be the main one.
+  @spec get_discogs_id(t()) :: integer() | nil
   def get_discogs_id(r) do
     candidates =
       r.relations
@@ -32,6 +43,7 @@ defmodule MusicBrainz.Artist do
     end
   end
 
+  @spec get_wikidata_id(t()) :: String.t() | nil
   def get_wikidata_id(r) do
     Enum.find_value(r.relations, fn relation ->
       if relation.type == "wikidata" do
@@ -40,6 +52,7 @@ defmodule MusicBrainz.Artist do
     end)
   end
 
+  @spec url(String.t()) :: String.t()
   def url(id) do
     "https://musicbrainz.org/artist/#{id}"
   end
diff --git a/lib/music_brainz/external_link.ex b/lib/music_brainz/external_link.ex
index 882a0ebd..123b8b27 100644
--- a/lib/music_brainz/external_link.ex
+++ b/lib/music_brainz/external_link.ex
@@ -1,6 +1,12 @@
 defmodule MusicBrainz.ExternalLink do
   defstruct [:name, :url]
 
+  @type t :: %__MODULE__{
+          name: atom(),
+          url: String.t()
+        }
+
+  @spec external_links(map(), map() | String.t() | nil) :: [t()] | [String.t()]
   def external_links(musicbrainz_data, patterns) when is_map(patterns) do
     Enum.reduce(patterns, [], fn {name, pattern}, acc ->
       case external_links(musicbrainz_data, pattern) do
diff --git a/lib/music_brainz/release.ex b/lib/music_brainz/release.ex
index 9863479c..15a6bb98 100644
--- a/lib/music_brainz/release.ex
+++ b/lib/music_brainz/release.ex
@@ -24,33 +24,73 @@ defmodule MusicBrainz.Release do
     :media
   ]
 
+  @type t :: %__MODULE__{
+          id: String.t(),
+          title: String.t(),
+          disambiguation: String.t() | nil,
+          packaging: String.t() | nil,
+          artists: [Artist.t()],
+          date: String.t() | nil,
+          barcode: String.t() | nil,
+          catalog_number: String.t(),
+          country: String.t() | nil,
+          media: [Medium.t()]
+        }
+
   defmodule Artist do
     @enforce_keys [:id, :name, :sort_name]
     defstruct [:id, :name, :sort_name]
+
+    @type t :: %__MODULE__{
+            id: String.t(),
+            name: String.t(),
+            sort_name: String.t()
+          }
   end
 
   defmodule Medium do
     @enforce_keys [:title, :format, :number, :track_count, :tracks]
     defstruct [:title, :format, :number, :track_count, :tracks]
+
+    @type t :: %__MODULE__{
+            title: String.t() | nil,
+            format: String.t() | nil,
+            number: non_neg_integer(),
+            track_count: non_neg_integer(),
+            tracks: [MusicBrainz.Release.Track.t()]
+          }
   end
 
   defmodule Track do
     @enforce_keys [:id, :title, :artists, :length, :number, :position]
     defstruct [:id, :title, :artists, :length, :number, :position]
+
+    @type t :: %__MODULE__{
+            id: String.t(),
+            title: String.t(),
+            artists: [MusicBrainz.Release.Artist.t()],
+            length: non_neg_integer() | nil,
+            number: String.t(),
+            position: non_neg_integer()
+          }
   end
 
+  @spec media_count(t()) :: non_neg_integer()
   def media_count(release) do
     Enum.count(release.media)
   end
 
+  @spec get_medium(t(), non_neg_integer()) :: Medium.t() | nil
   def get_medium(release, medium_number) do
     Enum.find(release.media, fn m -> m.number == medium_number end)
   end
 
+  @spec medium_duration(Medium.t()) :: non_neg_integer()
   def medium_duration(medium) do
     Enum.sum_by(medium.tracks, fn track -> track.length || 0 end)
   end
 
+  @spec medium_tracks(t(), non_neg_integer()) :: [Track.t()]
   def medium_tracks(release, medium_number) do
     case Enum.find(release.media, fn m -> m.number == medium_number end) do
       nil -> []
@@ -58,14 +98,17 @@ defmodule MusicBrainz.Release do
     end
   end
 
+  @spec release_duration(t()) :: non_neg_integer()
   def release_duration(release) do
     Enum.sum_by(release.media, fn medium -> medium_duration(medium) end)
   end
 
+  @spec tracks(t()) :: [Track.t()]
   def tracks(release) do
     Enum.flat_map(release.media, fn medium -> medium.tracks end)
   end
 
+  @spec from_api_response(map()) :: t()
   def from_api_response(r) do
     %__MODULE__{
       id: r["id"],
@@ -81,6 +124,7 @@ defmodule MusicBrainz.Release do
     }
   end
 
+  @spec thumb_url(t()) :: String.t()
   def thumb_url(release) do
     "https://coverartarchive.org/release/#{release.id}/front-250"
   end
diff --git a/lib/music_brainz/release_group.ex b/lib/music_brainz/release_group.ex
index c516faf2..5a6bb4e4 100644
--- a/lib/music_brainz/release_group.ex
+++ b/lib/music_brainz/release_group.ex
@@ -1,6 +1,7 @@
 defmodule MusicBrainz.ReleaseGroup do
   alias MusicBrainz.ReleaseGroupSearchResult
 
+  @spec included_release_groups(map()) :: [ReleaseGroupSearchResult.t()]
   def included_release_groups(release_group) do
     release_group
     |> get_release_groups()
@@ -9,27 +10,32 @@ defmodule MusicBrainz.ReleaseGroup do
     end)
   end
 
+  @spec releases(map()) :: [map()]
   def releases(release_group) do
     release_group
     |> Map.get("releases", [])
   end
 
+  @spec release_ids(map()) :: [String.t()]
   def release_ids(release_group) do
     release_group
     |> Map.get("releases", [])
     |> Enum.map(fn release -> release["id"] end)
   end
 
+  @spec included_release_group_ids(map()) :: [String.t()]
   def included_release_group_ids(release_group) do
     release_group
     |> included_release_groups()
     |> Enum.map(fn rg -> rg.id end)
   end
 
+  @spec url(String.t()) :: String.t()
   def url(id) do
     "https://musicbrainz.org/release-group/#{id}"
   end
 
+  @spec parse_type(String.t() | nil) :: :album | :ep | :live | :compilation | :single | :other
   def parse_type("Album"), do: :album
   def parse_type("EP"), do: :ep
   def parse_type("Live"), do: :live
diff --git a/lib/music_brainz/release_group_search_result.ex b/lib/music_brainz/release_group_search_result.ex
index 1092312d..751c10f6 100644
--- a/lib/music_brainz/release_group_search_result.ex
+++ b/lib/music_brainz/release_group_search_result.ex
@@ -4,6 +4,15 @@ defmodule MusicBrainz.ReleaseGroupSearchResult do
   @enforce_keys [:id, :type, :title, :artists, :release_date]
   defstruct [:id, :type, :title, :artists, :release_date]
 
+  @type t :: %__MODULE__{
+          id: String.t(),
+          type: :album | :ep | :live | :compilation | :single | :other,
+          title: String.t(),
+          artists: String.t(),
+          release_date: String.t() | nil
+        }
+
+  @spec from_api_response(map()) :: t()
   def from_api_response(rg) do
     %__MODULE__{
       id: rg["id"],
@@ -14,6 +23,7 @@ defmodule MusicBrainz.ReleaseGroupSearchResult do
     }
   end
 
+  @spec thumb_url(t()) :: String.t()
   def thumb_url(rgr) do
     "https://coverartarchive.org/release-group/#{rgr.id}/front-250"
   end
diff --git a/lib/music_brainz/release_search_result.ex b/lib/music_brainz/release_search_result.ex
index c4ea06eb..49889427 100644
--- a/lib/music_brainz/release_search_result.ex
+++ b/lib/music_brainz/release_search_result.ex
@@ -4,6 +4,17 @@ defmodule MusicBrainz.ReleaseSearchResult do
   @enforce_keys [:id, :title, :release_group, :artists, :date, :barcode, :media]
   defstruct [:id, :title, :release_group, :artists, :date, :barcode, :media]
 
+  @type t :: %__MODULE__{
+          id: String.t(),
+          title: String.t(),
+          release_group: map() | nil,
+          artists: String.t(),
+          date: String.t() | nil,
+          barcode: String.t() | nil,
+          media: [map()]
+        }
+
+  @spec from_api_response(map()) :: t()
   def from_api_response(r) do
     %__MODULE__{
       id: r["id"],
@@ -54,6 +65,8 @@ defmodule MusicBrainz.ReleaseSearchResult do
       :multi
 
   """
+  @spec format(t()) ::
+          :cd | :vinyl | :dvd | :blu_ray | :digital_download | :vhs | :multi | :unknown
   def format(release_search_result) do
     sorted_frequencies =
       release_search_result.media
@@ -74,6 +87,7 @@ defmodule MusicBrainz.ReleaseSearchResult do
     }
   end
 
+  @spec parse_media([map()]) :: [map()]
   def parse_media(media) do
     Enum.map(media, fn m ->
       %{
diff --git a/lib/music_library/artist_chat.ex b/lib/music_library/artist_chat.ex
index d24d5efc..d852e9ce 100644
--- a/lib/music_library/artist_chat.ex
+++ b/lib/music_library/artist_chat.ex
@@ -4,6 +4,8 @@ defmodule MusicLibrary.ArtistChat do
   alias MusicLibrary.Artists.ArtistInfo
 
   @impl true
+  @spec stream_response([map()], {map(), ArtistInfo.t()}, (String.t() -> any())) ::
+          :ok | {:error, term()}
   def stream_response(messages, {artist, artist_info}, callback) do
     instructions = build_instructions(artist, artist_info)
 
diff --git a/lib/music_library/artists.ex b/lib/music_library/artists.ex
index a82f5263..94174aa8 100644
--- a/lib/music_library/artists.ex
+++ b/lib/music_library/artists.ex
@@ -6,6 +6,7 @@ defmodule MusicLibrary.Artists do
   alias MusicLibrary.Records.{ArtistRecord, Record}
   alias MusicLibrary.{Repo, Worker}
 
+  @spec get_artist!(String.t()) :: map()
   def get_artist!(musicbrainz_id) do
     q =
       from ar in ArtistRecord,
@@ -16,6 +17,7 @@ defmodule MusicLibrary.Artists do
     Repo.one!(q)
   end
 
+  @spec get_similar_artists(map()) :: {:ok, [map()]} | {:error, term()}
   def get_similar_artists(artist) do
     case LastFm.get_similar_artists(artist.musicbrainz_id, artist.name) do
       {:ok, artists} ->
@@ -31,6 +33,7 @@ defmodule MusicLibrary.Artists do
     end
   end
 
+  @spec name_id_pairs([String.t()]) :: [{String.t(), String.t()}]
   def name_id_pairs(names) do
     q =
       from ar in ArtistRecord,
@@ -41,12 +44,14 @@ defmodule MusicLibrary.Artists do
     Repo.all(q)
   end
 
+  @spec get_all_artist_ids() :: MapSet.t(String.t())
   def get_all_artist_ids do
     q = from ar in ArtistRecord, distinct: true, select: ar.musicbrainz_id
 
     q |> Repo.all() |> MapSet.new()
   end
 
+  @spec get_all_artist_pairs() :: [map()]
   def get_all_artist_pairs do
     q =
       from ar in ArtistRecord,
@@ -56,6 +61,7 @@ defmodule MusicLibrary.Artists do
     q |> Repo.all()
   end
 
+  @spec get_image_hashes([map()]) :: %{String.t() => String.t() | nil}
   def get_image_hashes(lastfm_artists) do
     musicbrainz_ids = Enum.map(lastfm_artists, & &1.musicbrainz_id)
 
@@ -69,6 +75,7 @@ defmodule MusicLibrary.Artists do
     |> Enum.into(%{})
   end
 
+  @spec exists?(String.t()) :: boolean()
   def exists?(artist_id) do
     q =
       from ar in ArtistRecord,
@@ -77,10 +84,12 @@ defmodule MusicLibrary.Artists do
     Repo.exists?(q)
   end
 
+  @spec delete_artist_info(String.t()) :: {non_neg_integer(), nil | [term()]}
   def delete_artist_info(artist_id) do
     Repo.delete_all(from ai in ArtistInfo, where: ai.id == ^artist_id)
   end
 
+  @spec fetch_artist_info(String.t()) :: {:ok, ArtistInfo.t()} | {:error, term()}
   def fetch_artist_info(artist_id) do
     with {:ok, musicbrainz_artist} <- MusicBrainz.get_artist(artist_id) do
       if discogs_id = MusicBrainz.Artist.get_discogs_id(musicbrainz_artist) do
@@ -100,6 +109,7 @@ defmodule MusicLibrary.Artists do
     end
   end
 
+  @spec refresh_musicbrainz_data(String.t()) :: {:ok, ArtistInfo.t()} | {:error, term()}
   def refresh_musicbrainz_data(artist_id) do
     with {:ok, musicbrainz_artist} <- MusicBrainz.get_artist(artist_id) do
       get_artist_info!(artist_id)
@@ -108,10 +118,13 @@ defmodule MusicLibrary.Artists do
     end
   end
 
+  @spec refresh_musicbrainz_data_async(ArtistInfo.t()) ::
+          {:ok, Oban.Job.t()} | {:error, Ecto.Changeset.t()}
   def refresh_musicbrainz_data_async(artist_info) do
     enqueue_worker(Worker.ArtistRefreshMusicBrainzData, %{"id" => artist_info.id})
   end
 
+  @spec refresh_discogs_data(String.t()) :: {:ok, ArtistInfo.t()} | {:error, term()}
   def refresh_discogs_data(artist_id) do
     artist_info = get_artist_info!(artist_id)
 
@@ -130,10 +143,13 @@ defmodule MusicLibrary.Artists do
     end
   end
 
+  @spec refresh_discogs_data_async(ArtistInfo.t()) ::
+          {:ok, Oban.Job.t()} | {:error, Ecto.Changeset.t()}
   def refresh_discogs_data_async(artist_info) do
     enqueue_worker(Worker.ArtistRefreshDiscogsData, %{"id" => artist_info.id})
   end
 
+  @spec fetch_wikipedia_data(String.t()) :: {:ok, ArtistInfo.t()} | {:error, term()}
   def fetch_wikipedia_data(artist_id) do
     artist_info = get_artist_info!(artist_id)
 
@@ -152,24 +168,30 @@ defmodule MusicLibrary.Artists do
     end
   end
 
+  @spec refresh_wikipedia_data(String.t()) :: {:ok, ArtistInfo.t()} | {:error, term()}
   def refresh_wikipedia_data(artist_id) do
     fetch_wikipedia_data(artist_id)
   end
 
+  @spec refresh_wikipedia_data_async(ArtistInfo.t()) ::
+          {:ok, Oban.Job.t()} | {:error, Ecto.Changeset.t()}
   def refresh_wikipedia_data_async(artist_info) do
     enqueue_worker(Worker.ArtistRefreshWikipediaData, %{"id" => artist_info.id})
   end
 
+  @spec create_artist_info(map()) :: {:ok, ArtistInfo.t()} | {:error, Ecto.Changeset.t()}
   def create_artist_info(attrs) do
     %ArtistInfo{}
     |> ArtistInfo.changeset(attrs)
     |> Repo.insert(on_conflict: {:replace, [:musicbrainz_data, :discogs_data]})
   end
 
+  @spec get_artist_info!(String.t()) :: ArtistInfo.t()
   def get_artist_info!(artist_id) do
     Repo.get!(ArtistInfo, artist_id)
   end
 
+  @spec get_artist_infos([String.t()]) :: [ArtistInfo.t()]
   def get_artist_infos(artist_ids) do
     q =
       from ai in ArtistInfo, where: ai.id in ^artist_ids
@@ -177,6 +199,7 @@ defmodule MusicLibrary.Artists do
     Repo.all(q)
   end
 
+  @spec fetch_image(String.t()) :: {:ok, ArtistInfo.t()} | {:error, term()}
   def fetch_image(artist_id) do
     artist_info = get_artist_info!(artist_id)
 
@@ -191,6 +214,7 @@ defmodule MusicLibrary.Artists do
     end
   end
 
+  @spec fetch_lastfm_data(String.t()) :: {:ok, ArtistInfo.t()} | {:error, term()}
   def fetch_lastfm_data(artist_id) do
     artist_info = get_artist_info!(artist_id)
     name = get_in(artist_info.musicbrainz_data, ["name"]) || ""
@@ -208,26 +232,36 @@ defmodule MusicLibrary.Artists do
     end
   end
 
+  @spec fetch_lastfm_data_async(String.t()) ::
+          {:ok, Oban.Job.t()} | {:error, Ecto.Changeset.t()}
   def fetch_lastfm_data_async(artist_id) do
     enqueue_worker(Worker.FetchArtistLastFmData, %{"id" => artist_id})
   end
 
+  @spec fetch_artist_info_async(String.t()) ::
+          {:ok, Oban.Job.t()} | {:error, Ecto.Changeset.t()}
   def fetch_artist_info_async(artist_id) do
     enqueue_worker(Worker.FetchArtistInfo, %{"id" => artist_id})
   end
 
+  @spec fetch_image_async(String.t()) :: {:ok, Oban.Job.t()} | {:error, Ecto.Changeset.t()}
   def fetch_image_async(artist_id) do
     enqueue_worker(Worker.FetchArtistImage, %{"id" => artist_id})
   end
 
+  @spec prune_artist_info_async(String.t()) ::
+          {:ok, Oban.Job.t()} | {:error, Ecto.Changeset.t()}
   def prune_artist_info_async(artist_id) do
     enqueue_worker(Worker.PruneArtistInfo, %{"id" => artist_id})
   end
 
+  @spec change_artist_info(ArtistInfo.t(), map()) :: Ecto.Changeset.t()
   def change_artist_info(artist_info, attrs \\ %{}) do
     ArtistInfo.changeset(artist_info, attrs)
   end
 
+  @spec update_artist_info(ArtistInfo.t(), map()) ::
+          {:ok, ArtistInfo.t()} | {:error, Ecto.Changeset.t()}
   def update_artist_info(artist_info, attrs) do
     artist_info
     |> ArtistInfo.changeset(attrs)
diff --git a/lib/music_library/artists/artist.ex b/lib/music_library/artists/artist.ex
index 52eee011..349a16ae 100644
--- a/lib/music_library/artists/artist.ex
+++ b/lib/music_library/artists/artist.ex
@@ -11,6 +11,9 @@ defmodule MusicLibrary.Artists.Artist do
     field :joinphrase, :string, default: ""
   end
 
+  @type t :: %__MODULE__{}
+
+  @spec changeset(t() | Ecto.Changeset.t(), map()) :: Ecto.Changeset.t()
   def changeset(artist, attrs) do
     artist
     |> cast(attrs, [:name, :sort_name, :disambiguation, :joinphrase, :musicbrainz_id])
diff --git a/lib/music_library/artists/artist_info.ex b/lib/music_library/artists/artist_info.ex
index 6a49b8cb..9a5b6102 100644
--- a/lib/music_library/artists/artist_info.ex
+++ b/lib/music_library/artists/artist_info.ex
@@ -19,6 +19,9 @@ defmodule MusicLibrary.Artists.ArtistInfo do
     timestamps(type: :utc_datetime)
   end
 
+  @type t :: %__MODULE__{}
+
+  @spec changeset(t() | Ecto.Changeset.t(), map()) :: Ecto.Changeset.t()
   def changeset(artist_info, attrs) do
     artist_info
     |> cast(attrs, [
@@ -32,6 +35,7 @@ defmodule MusicLibrary.Artists.ArtistInfo do
     |> validate_required([:musicbrainz_data])
   end
 
+  @spec country(t()) :: %{name: String.t(), code: String.t()}
   def country(artist_info) do
     %{"area" => area} =
       artist_info.musicbrainz_data
@@ -45,6 +49,9 @@ defmodule MusicLibrary.Artists.ArtistInfo do
     %{name: area["name"] || "World", code: country_code || "XW"}
   end
 
+  @spec extract_image(t()) ::
+          {:ok, %{url: String.t(), width: integer()}}
+          | {:error, :no_discogs_data | :image_not_found}
   def extract_image(artist_info) when is_nil(artist_info.discogs_data) do
     {:error, :no_discogs_data}
   end
@@ -71,9 +78,11 @@ defmodule MusicLibrary.Artists.ArtistInfo do
     "ProgArchives" => "progarchives.com"
   }
 
+  @spec external_links(t()) :: [map()]
   def external_links(artist_info),
     do: ExternalLink.external_links(artist_info.musicbrainz_data, @external_link_patterns)
 
+  @spec discogs_id(t()) :: integer() | nil
   def discogs_id(artist_info) do
     case artist_info.discogs_data do
       %{"id" => discogs_id} -> discogs_id
@@ -81,6 +90,7 @@ defmodule MusicLibrary.Artists.ArtistInfo do
     end
   end
 
+  @spec wikidata_id(t()) :: String.t() | nil
   def wikidata_id(artist_info) do
     relations = get_in(artist_info.musicbrainz_data, ["relations"]) || []
 
@@ -93,27 +103,33 @@ defmodule MusicLibrary.Artists.ArtistInfo do
     end)
   end
 
+  @spec wikipedia_bio(t()) :: String.t() | nil
   def wikipedia_bio(artist_info) do
     get_in(artist_info.wikipedia_data, ["intro_html"]) ||
       get_in(artist_info.wikipedia_data, ["extract_html"])
   end
 
+  @spec wikipedia_summary(t()) :: String.t() | nil
   def wikipedia_summary(artist_info) do
     get_in(artist_info.wikipedia_data, ["extract"])
   end
 
+  @spec wikipedia_url(t()) :: String.t() | nil
   def wikipedia_url(artist_info) do
     get_in(artist_info.wikipedia_data, ["content_urls", "desktop", "page"])
   end
 
+  @spec wikipedia_description(t()) :: String.t() | nil
   def wikipedia_description(artist_info) do
     get_in(artist_info.wikipedia_data, ["description"])
   end
 
+  @spec lastfm_tags(t()) :: [map()]
   def lastfm_tags(artist_info) do
     get_in(artist_info.lastfm_data, ["tags"]) || []
   end
 
+  @spec lastfm_similar_artists(t()) :: [map()]
   def lastfm_similar_artists(artist_info) do
     get_in(artist_info.lastfm_data, ["similar_artists"]) || []
   end
diff --git a/lib/music_library/artists/batch.ex b/lib/music_library/artists/batch.ex
index edb4e417..e1c7bf22 100644
--- a/lib/music_library/artists/batch.ex
+++ b/lib/music_library/artists/batch.ex
@@ -5,24 +5,28 @@ defmodule MusicLibrary.Artists.Batch do
   alias MusicLibrary.Artists.ArtistInfo
   alias MusicLibrary.Batch
 
+  @spec refresh_musicbrainz_data() :: {:ok, [String.t()]}
   def refresh_musicbrainz_data do
     Batch.run_on_all(from(r in ArtistInfo), "artist_info", fn artist_info ->
       Artists.refresh_musicbrainz_data_async(artist_info)
     end)
   end
 
+  @spec refresh_discogs_data() :: {:ok, [String.t()]}
   def refresh_discogs_data do
     Batch.run_on_all(from(r in ArtistInfo), "artist_info", fn artist_info ->
       Artists.refresh_discogs_data_async(artist_info)
     end)
   end
 
+  @spec refresh_wikipedia_data() :: {:ok, [String.t()]}
   def refresh_wikipedia_data do
     Batch.run_on_all(from(r in ArtistInfo), "artist_info", fn artist_info ->
       Artists.refresh_wikipedia_data_async(artist_info)
     end)
   end
 
+  @spec refresh_lastfm_data() :: {:ok, [String.t()]}
   def refresh_lastfm_data do
     Batch.run_on_all(from(r in ArtistInfo), "artist_info", fn artist_info ->
       Artists.fetch_lastfm_data_async(artist_info.id)
diff --git a/lib/music_library/assets.ex b/lib/music_library/assets.ex
index 9a6c0176..9bd1c8a0 100644
--- a/lib/music_library/assets.ex
+++ b/lib/music_library/assets.ex
@@ -8,6 +8,7 @@ defmodule MusicLibrary.Assets do
   Store any file type - the responsibility to correctly populate format and
   properties is left to the caller.
   """
+  @spec store(map()) :: {:ok, Asset.t()} | {:error, Ecto.Changeset.t()}
   def store(params) do
     %Asset{}
     |> Asset.changeset(params)
@@ -17,20 +18,24 @@ defmodule MusicLibrary.Assets do
   @doc """
   Store image files - properties will be computed automatically.
   """
+  @spec store_image(map()) :: {:ok, Asset.t()} | {:error, Ecto.Changeset.t()}
   def store_image(params) do
     %Asset{}
     |> Asset.image_changeset(params)
     |> Repo.insert(on_conflict: :nothing, returning: true)
   end
 
+  @spec get(String.t()) :: Asset.t() | nil
   def get(hash) do
     Repo.get(Asset, hash)
   end
 
+  @spec get!(String.t()) :: Asset.t()
   def get!(hash) do
     Repo.get!(Asset, hash)
   end
 
+  @spec total_content_size() :: non_neg_integer() | nil
   def total_content_size do
     q =
       from p in Asset, select: sum(fragment("length(content)"))
@@ -38,6 +43,7 @@ defmodule MusicLibrary.Assets do
     Repo.one(q)
   end
 
+  @spec track_total_content_size() :: :ok
   def track_total_content_size do
     :telemetry.execute(
       [:music_library, :assets],
@@ -46,6 +52,7 @@ defmodule MusicLibrary.Assets do
     )
   end
 
+  @spec track_total_cache_size() :: :ok
   def track_total_cache_size do
     :telemetry.execute(
       [:music_library, :assets],
diff --git a/lib/music_library/assets/asset.ex b/lib/music_library/assets/asset.ex
index 5fdb1643..d57acd33 100644
--- a/lib/music_library/assets/asset.ex
+++ b/lib/music_library/assets/asset.ex
@@ -14,6 +14,9 @@ defmodule MusicLibrary.Assets.Asset do
     timestamps(type: :utc_datetime)
   end
 
+  @type t :: %__MODULE__{}
+
+  @spec changeset(t() | Ecto.Changeset.t(), map()) :: Ecto.Changeset.t()
   def changeset(asset, attrs) do
     asset
     |> cast(attrs, [:content, :format, :properties])
@@ -22,6 +25,7 @@ defmodule MusicLibrary.Assets.Asset do
     |> unique_constraint(:hash)
   end
 
+  @spec image_changeset(t() | Ecto.Changeset.t(), map()) :: Ecto.Changeset.t()
   def image_changeset(asset, attrs) do
     asset
     |> cast(attrs, [:content, :format])
@@ -60,6 +64,7 @@ defmodule MusicLibrary.Assets.Asset do
     }
   end
 
+  @spec hash(binary()) :: String.t()
   def hash(content) do
     :crypto.hash(:sha256, content) |> Base.encode16()
   end
diff --git a/lib/music_library/assets/cache.ex b/lib/music_library/assets/cache.ex
index 00dfd362..0bb815b5 100644
--- a/lib/music_library/assets/cache.ex
+++ b/lib/music_library/assets/cache.ex
@@ -1,13 +1,16 @@
 defmodule MusicLibrary.Assets.Cache do
+  @spec new() :: :ets.table()
   def new do
     :ets.new(__MODULE__, [:named_table, :public, :compressed, read_concurrency: true])
   end
 
+  @spec set(String.t(), String.t(), binary()) :: true
   def set(payload, format, content) do
     inserted_at = DateTime.utc_now() |> DateTime.to_unix()
     :ets.insert(__MODULE__, {{payload, format}, inserted_at, content})
   end
 
+  @spec get(String.t(), String.t()) :: {:found, binary()} | :not_found
   def get(payload, format) do
     case :ets.lookup(__MODULE__, {payload, format}) do
       [{{^payload, ^format}, _inserted_at, content}] -> {:found, content}
@@ -15,6 +18,7 @@ defmodule MusicLibrary.Assets.Cache do
     end
   end
 
+  @spec total_content_size() :: non_neg_integer()
   def total_content_size do
     :ets.foldl(
       fn {_key, _inserted_at, content}, acc -> acc + byte_size(content) end,
@@ -23,6 +27,7 @@ defmodule MusicLibrary.Assets.Cache do
     )
   end
 
+  @spec prune(non_neg_integer()) :: non_neg_integer()
   def prune(older_than_seconds) do
     threshold =
       DateTime.utc_now()
diff --git a/lib/music_library/assets/image.ex b/lib/music_library/assets/image.ex
index 7041de57..8eaceaa7 100644
--- a/lib/music_library/assets/image.ex
+++ b/lib/music_library/assets/image.ex
@@ -9,13 +9,16 @@ defmodule MusicLibrary.Assets.Image do
   @default_size 2000
   @default_format "image/jpeg"
 
+  @spec fallback_data() :: binary()
   def fallback_data, do: unquote(fallback_data)
 
+  @spec resize(binary(), pos_integer(), String.t()) :: {:ok, binary()} | {:error, term()}
   def resize(cover_data, size \\ @default_size, format \\ @default_format) do
     {:ok, thumb} = Operation.thumbnail_buffer(cover_data, size)
     Image.write_to_buffer(thumb, extension(format))
   end
 
+  @spec convert(binary(), String.t(), String.t()) :: {:ok, binary()}
   def convert(cover_data, data_format, target_format) do
     if data_format == target_format do
       {:ok, cover_data}
diff --git a/lib/music_library/assets/transform.ex b/lib/music_library/assets/transform.ex
index 83c4936f..f15fc685 100644
--- a/lib/music_library/assets/transform.ex
+++ b/lib/music_library/assets/transform.ex
@@ -5,6 +5,7 @@ defmodule MusicLibrary.Assets.Transform do
   @type t :: %__MODULE__{}
   @type payload :: String.t()
 
+  @spec new(map()) :: t()
   def new(attrs \\ %{}), do: struct!(__MODULE__, attrs)
 
   @doc """
diff --git a/lib/music_library/barcode_scan.ex b/lib/music_library/barcode_scan.ex
index c73c7ffd..861cf54f 100644
--- a/lib/music_library/barcode_scan.ex
+++ b/lib/music_library/barcode_scan.ex
@@ -2,6 +2,7 @@ defmodule MusicLibrary.BarcodeScan do
   alias MusicLibrary.BarcodeScan.Result
   alias MusicLibrary.Records
 
+  @spec scan(String.t()) :: {:ok, Result.t()} | {:error, term()}
   def scan(number) do
     case MusicBrainz.search_release_by_barcode(number) do
       {:ok, [best_match_release | _other_releases]} ->
@@ -26,6 +27,7 @@ defmodule MusicLibrary.BarcodeScan do
     end
   end
 
+  @spec import_results([Result.t()], DateTime.t()) :: [{String.t(), term()}]
   def import_results(scan_results, current_time) do
     Enum.reduce(scan_results, [], fn scan_result, errors ->
       case import_result(scan_result, current_time) do
diff --git a/lib/music_library/barcode_scan/result.ex b/lib/music_library/barcode_scan/result.ex
index 9e2c0ed2..5b3caa96 100644
--- a/lib/music_library/barcode_scan/result.ex
+++ b/lib/music_library/barcode_scan/result.ex
@@ -1,6 +1,14 @@
 defmodule MusicLibrary.BarcodeScan.Result do
   defstruct [:status, :number, :record_id, :release]
 
+  @type t :: %__MODULE__{
+          status: :new | :wishlisted | :collected | :not_found,
+          number: String.t(),
+          record_id: String.t() | nil,
+          release: map() | nil
+        }
+
+  @spec new(String.t(), map()) :: t()
   def new(number, release) do
     %__MODULE__{
       number: number,
@@ -9,6 +17,7 @@ defmodule MusicLibrary.BarcodeScan.Result do
     }
   end
 
+  @spec wishlisted(String.t(), String.t(), map()) :: t()
   def wishlisted(number, record_id, release) do
     %__MODULE__{
       number: number,
@@ -18,6 +27,7 @@ defmodule MusicLibrary.BarcodeScan.Result do
     }
   end
 
+  @spec collected(String.t(), String.t(), map()) :: t()
   def collected(number, record_id, release) do
     %__MODULE__{
       number: number,
@@ -27,6 +37,7 @@ defmodule MusicLibrary.BarcodeScan.Result do
     }
   end
 
+  @spec not_found(String.t()) :: t()
   def not_found(number) do
     %__MODULE__{
       number: number,
diff --git a/lib/music_library/batch.ex b/lib/music_library/batch.ex
index f474acb7..4d24db50 100644
--- a/lib/music_library/batch.ex
+++ b/lib/music_library/batch.ex
@@ -3,6 +3,9 @@ defmodule MusicLibrary.Batch do
 
   require Logger
 
+  @spec run_on_all(Ecto.Queryable.t(), String.t(), (struct() ->
+                                                      :ok | {:ok, term()} | {:error, term()})) ::
+          {:ok, [String.t()]}
   def run_on_all(queryable, label, fun) do
     stream = Repo.stream(queryable, max_rows: 50)
 
diff --git a/lib/music_library/collection.ex b/lib/music_library/collection.ex
index e9bf57f9..cd064b86 100644
--- a/lib/music_library/collection.ex
+++ b/lib/music_library/collection.ex
@@ -8,6 +8,7 @@ defmodule MusicLibrary.Collection do
 
   @pagination Application.compile_env!(:music_library, :pagination)
 
+  @spec search_records(String.t(), MusicLibrary.Types.pagination_opts()) :: [SearchIndex.t()]
   def search_records(query, opts \\ []) do
     limit = Keyword.get(opts, :limit, @pagination[:default_page_size])
     offset = Keyword.get(opts, :offset, 0)
@@ -16,10 +17,12 @@ defmodule MusicLibrary.Collection do
     Records.search_records(base_search(), query, limit: limit, offset: offset, order: order)
   end
 
+  @spec search_records_count(String.t()) :: non_neg_integer()
   def search_records_count(query) do
     Records.search_records_count(base_search(), query)
   end
 
+  @spec count_records_by_format() :: [{String.t(), non_neg_integer()}]
   def count_records_by_format do
     q =
       from r in Record,
@@ -31,6 +34,7 @@ defmodule MusicLibrary.Collection do
     Repo.all(q)
   end
 
+  @spec count_records_by_type() :: [{String.t(), non_neg_integer()}]
   def count_records_by_type do
     q =
       from r in Record,
@@ -42,6 +46,7 @@ defmodule MusicLibrary.Collection do
     Repo.all(q)
   end
 
+  @spec get_records_on_this_day(Date.t()) :: [SearchIndex.t()]
   def get_records_on_this_day(date \\ Date.utc_today()) do
     month_day = Calendar.strftime(date, "%m-%d")
 
@@ -55,6 +60,7 @@ defmodule MusicLibrary.Collection do
     Repo.all(q)
   end
 
+  @spec get_latest_record() :: SearchIndex.t() | nil
   def get_latest_record do
     q =
       from r in Record,
@@ -66,6 +72,7 @@ defmodule MusicLibrary.Collection do
     Repo.one(q)
   end
 
+  @spec get_latest_record!() :: SearchIndex.t()
   def get_latest_record! do
     q =
       from r in Record,
@@ -77,6 +84,7 @@ defmodule MusicLibrary.Collection do
     Repo.one!(q)
   end
 
+  @spec get_random_record!() :: SearchIndex.t()
   def get_random_record! do
     q =
       from r in Record,
@@ -88,6 +96,7 @@ defmodule MusicLibrary.Collection do
     Repo.one!(q)
   end
 
+  @spec count_records_by_artist(keyword()) :: [map()]
   def count_records_by_artist(opts \\ []) do
     limit = Keyword.get(opts, :limit, @pagination[:stats_limit])
 
@@ -106,6 +115,7 @@ defmodule MusicLibrary.Collection do
     Repo.all(q)
   end
 
+  @spec count_records_by_genre(keyword()) :: [{String.t(), non_neg_integer()}]
   def count_records_by_genre(opts \\ []) do
     limit = Keyword.get(opts, :limit, @pagination[:stats_limit])
 
@@ -122,6 +132,7 @@ defmodule MusicLibrary.Collection do
     Repo.all(q)
   end
 
+  @spec collected_releases_query() :: Ecto.Query.t()
   def collected_releases_query do
     from rr in RecordRelease,
       where: not is_nil(rr.purchased_at),
diff --git a/lib/music_library/colors/k_means_extractor.ex b/lib/music_library/colors/k_means_extractor.ex
index 756115cd..42b30d81 100644
--- a/lib/music_library/colors/k_means_extractor.ex
+++ b/lib/music_library/colors/k_means_extractor.ex
@@ -5,6 +5,7 @@ defmodule MusicLibrary.Colors.KMeansExtractor do
 
   alias Vix.Vips.Image
 
+  @spec extract_dominant_colors(binary(), pos_integer()) :: {:ok, [String.t()]} | {:error, term()}
   def extract_dominant_colors(image_data, num_colors \\ 5) do
     with {:ok, dir} <- Briefly.create(type: :directory),
          path = dir <> "/temp_image.jpg",
diff --git a/lib/music_library/format_number.ex b/lib/music_library/format_number.ex
index f9bd3451..d7fe3ce1 100644
--- a/lib/music_library/format_number.ex
+++ b/lib/music_library/format_number.ex
@@ -29,6 +29,7 @@ defmodule MusicLibrary.FormatNumber do
   Numbers less than 1,000 are returned as-is.
   Numbers 1,000 and above are formatted with appropriate suffix and one decimal place.
   """
+  @spec to_compact(integer()) :: String.t()
   def to_compact(number) when is_integer(number) and number < 1000 do
     Integer.to_string(number)
   end
diff --git a/lib/music_library/listening_stats.ex b/lib/music_library/listening_stats.ex
index 8330c53d..364d35f0 100644
--- a/lib/music_library/listening_stats.ex
+++ b/lib/music_library/listening_stats.ex
@@ -14,10 +14,19 @@ defmodule MusicLibrary.ListeningStats do
 
   @pagination Application.compile_env!(:music_library, :pagination)
 
+  @type period_opts :: [
+          period: atom(),
+          limit: non_neg_integer(),
+          current_time: DateTime.t(),
+          timezone: String.t()
+        ]
+
+  @spec scrobble_count() :: non_neg_integer()
   def scrobble_count do
     Repo.aggregate(Track, :count, :scrobbled_at_uts)
   end
 
+  @spec recent_activity(String.t(), non_neg_integer()) :: map()
   def recent_activity(timezone, limit \\ 100) do
     # When we get recent tracks, we need to:
     #
@@ -81,6 +90,7 @@ defmodule MusicLibrary.ListeningStats do
     }
   end
 
+  @spec localize_scrobbled_at(integer(), String.t()) :: String.t()
   def localize_scrobbled_at(uts, timezone) do
     ldt =
       uts
@@ -94,6 +104,7 @@ defmodule MusicLibrary.ListeningStats do
   Gets top albums for the specified time periods (7, 30, 90, 365 days) and all
   time. Returns a list of maps with album information and play counts.
   """
+  @spec get_top_albums_by_period(period_opts()) :: [map()]
   def get_top_albums_by_period(opts) do
     case Keyword.get(opts, :period, :last_7_days) do
       :all_time -> get_top_albums(opts)
@@ -107,6 +118,7 @@ defmodule MusicLibrary.ListeningStats do
   @doc """
   Gets top artists for a time period (7, 30, 90, 365 days) and all time.
   """
+  @spec get_top_artists_by_period(period_opts()) :: [map()]
   def get_top_artists_by_period(opts) do
     case Keyword.get(opts, :period, :last_7_days) do
       :all_time -> get_top_artists(opts)
@@ -121,6 +133,7 @@ defmodule MusicLibrary.ListeningStats do
   Gets the top albums by scrobble count across all time.
   Returns a list of maps with album information and play counts.
   """
+  @spec get_top_albums(period_opts()) :: [map()]
   def get_top_albums(opts) do
     limit = Keyword.get(opts, :limit, @pagination[:top_items_limit])
 
@@ -133,6 +146,7 @@ defmodule MusicLibrary.ListeningStats do
   Gets the top albums by scrobble count for the given number of days.
   Returns a list of maps with album information and play counts.
   """
+  @spec get_top_albums_by_days(pos_integer(), period_opts()) :: [map()]
   def get_top_albums_by_days(days, opts) do
     limit = Keyword.get(opts, :limit, @pagination[:top_items_limit])
     cutoff_timestamp = cutoff_timestamp(days, opts)
@@ -147,6 +161,7 @@ defmodule MusicLibrary.ListeningStats do
   Gets the top artists by scrobble count across all time.
   Returns a list of maps with artist information and play counts.
   """
+  @spec get_top_artists(period_opts()) :: [map()]
   def get_top_artists(opts) do
     limit = Keyword.get(opts, :limit, @pagination[:top_items_limit])
 
@@ -159,6 +174,7 @@ defmodule MusicLibrary.ListeningStats do
   Gets the top artists by scrobble count for the given number of days.
   Returns a list of maps with artist information and play counts.
   """
+  @spec get_top_artists_by_days(pos_integer(), period_opts()) :: [map()]
   def get_top_artists_by_days(days, opts) do
     limit = Keyword.get(opts, :limit, @pagination[:top_items_limit])
     cutoff_timestamp = cutoff_timestamp(days, opts)
diff --git a/lib/music_library/maintenance.ex b/lib/music_library/maintenance.ex
index 02535940..1ff71578 100644
--- a/lib/music_library/maintenance.ex
+++ b/lib/music_library/maintenance.ex
@@ -13,6 +13,7 @@ defmodule MusicLibrary.Maintenance do
 
   Active jobs are those in "available", "scheduled", "executing", or "retryable" states.
   """
+  @spec count_active_jobs(String.t()) :: non_neg_integer() | nil
   def count_active_jobs(worker) do
     query =
       from j in Oban.Job,
@@ -26,6 +27,7 @@ defmodule MusicLibrary.Maintenance do
   @doc """
   Runs VACUUM on the main database.
   """
+  @spec vacuum() :: :ok
   def vacuum do
     Repo.vacuum()
   end
@@ -33,6 +35,7 @@ defmodule MusicLibrary.Maintenance do
   @doc """
   Runs PRAGMA optimize on the main database.
   """
+  @spec optimize() :: :ok
   def optimize do
     Repo.optimize()
   end
diff --git a/lib/music_library/notes.ex b/lib/music_library/notes.ex
index f2609c3a..16c9ffc2 100644
--- a/lib/music_library/notes.ex
+++ b/lib/music_library/notes.ex
@@ -2,22 +2,26 @@ defmodule MusicLibrary.Notes do
   alias MusicLibrary.Notes.Note
   alias MusicLibrary.Repo
 
+  @spec get_note(atom(), String.t()) :: Note.t() | nil
   def get_note(entity, musicbrainz_id) do
     Repo.get_by(Note, entity: entity, musicbrainz_id: musicbrainz_id)
   end
 
+  @spec create_note(Note.t(), map()) :: {:ok, Note.t()} | {:error, Ecto.Changeset.t()}
   def create_note(note, attrs) do
     note
     |> Note.changeset(attrs)
     |> Repo.insert()
   end
 
+  @spec update_note(Note.t(), map()) :: {:ok, Note.t()} | {:error, Ecto.Changeset.t()}
   def update_note(note, attrs) do
     note
     |> Note.changeset(attrs)
     |> Repo.update()
   end
 
+  @spec change_note(Note.t(), map()) :: Ecto.Changeset.t()
   def change_note(note, attrs) do
     Note.changeset(note, attrs)
   end
diff --git a/lib/music_library/notes/note.ex b/lib/music_library/notes/note.ex
index 45e96dd1..3ff2e177 100644
--- a/lib/music_library/notes/note.ex
+++ b/lib/music_library/notes/note.ex
@@ -12,6 +12,9 @@ defmodule MusicLibrary.Notes.Note do
     timestamps(type: :utc_datetime)
   end
 
+  @type t :: %__MODULE__{}
+
+  @spec changeset(t() | Ecto.Changeset.t(), map()) :: Ecto.Changeset.t()
   def changeset(note, attrs) do
     note
     |> cast(attrs, [
diff --git a/lib/music_library/online_store_templates.ex b/lib/music_library/online_store_templates.ex
index 2cbeafc6..f0e9fed2 100644
--- a/lib/music_library/online_store_templates.ex
+++ b/lib/music_library/online_store_templates.ex
@@ -8,6 +8,7 @@ defmodule MusicLibrary.OnlineStoreTemplates do
   alias MusicLibrary.OnlineStoreTemplates.OnlineStoreTemplate
   alias MusicLibrary.Repo
 
+  @spec list_enabled_templates() :: [OnlineStoreTemplate.t()]
   def list_enabled_templates do
     OnlineStoreTemplate
     |> where([t], t.enabled == true)
@@ -15,34 +16,43 @@ defmodule MusicLibrary.OnlineStoreTemplates do
     |> Repo.all()
   end
 
+  @spec list_templates() :: [OnlineStoreTemplate.t()]
   def list_templates do
     OnlineStoreTemplate
     |> order_by([t], fragment("? COLLATE NOCASE ASC", t.name))
     |> Repo.all()
   end
 
+  @spec get_template!(String.t()) :: OnlineStoreTemplate.t()
   def get_template!(id), do: Repo.get!(OnlineStoreTemplate, id)
 
+  @spec create_template(map()) :: {:ok, OnlineStoreTemplate.t()} | {:error, Ecto.Changeset.t()}
   def create_template(attrs \\ %{}) do
     %OnlineStoreTemplate{}
     |> OnlineStoreTemplate.changeset(attrs)
     |> Repo.insert()
   end
 
+  @spec update_template(OnlineStoreTemplate.t(), map()) ::
+          {:ok, OnlineStoreTemplate.t()} | {:error, Ecto.Changeset.t()}
   def update_template(%OnlineStoreTemplate{} = template, attrs) do
     template
     |> OnlineStoreTemplate.changeset(attrs)
     |> Repo.update()
   end
 
+  @spec delete_template(OnlineStoreTemplate.t()) ::
+          {:ok, OnlineStoreTemplate.t()} | {:error, Ecto.Changeset.t()}
   def delete_template(%OnlineStoreTemplate{} = template) do
     Repo.delete(template)
   end
 
+  @spec change_template(OnlineStoreTemplate.t(), map()) :: Ecto.Changeset.t()
   def change_template(%OnlineStoreTemplate{} = template, attrs \\ %{}) do
     OnlineStoreTemplate.changeset(template, attrs)
   end
 
+  @spec generate_url(OnlineStoreTemplate.t(), map()) :: String.t()
   def generate_url(template, record) do
     artists_string = Enum.map_join(record.artists, " ", & &1.name)
     format_string = Atom.to_string(record.format)
diff --git a/lib/music_library/online_store_templates/online_store_template.ex b/lib/music_library/online_store_templates/online_store_template.ex
index 86dc7574..76e43d3a 100644
--- a/lib/music_library/online_store_templates/online_store_template.ex
+++ b/lib/music_library/online_store_templates/online_store_template.ex
@@ -14,7 +14,10 @@ defmodule MusicLibrary.OnlineStoreTemplates.OnlineStoreTemplate do
     timestamps(type: :utc_datetime)
   end
 
+  @type t :: %__MODULE__{}
+
   @doc false
+  @spec changeset(t() | Ecto.Changeset.t(), map()) :: Ecto.Changeset.t()
   def changeset(template, attrs) do
     template
     |> cast(attrs, [:name, :description, :url_template, :enabled])
diff --git a/lib/music_library/record_chat.ex b/lib/music_library/record_chat.ex
index e96ae60f..51a169c1 100644
--- a/lib/music_library/record_chat.ex
+++ b/lib/music_library/record_chat.ex
@@ -4,6 +4,8 @@ defmodule MusicLibrary.RecordChat do
   alias MusicLibrary.Records.Record
 
   @impl true
+  @spec stream_response([map()], {Record.t(), String.t() | nil}, (String.t() -> any())) ::
+          :ok | {:error, term()}
   def stream_response(messages, {record, embedding_text}, callback) do
     instructions = build_instructions(record, embedding_text)
 
diff --git a/lib/music_library/record_sets.ex b/lib/music_library/record_sets.ex
index 3695263d..0b15cfa4 100644
--- a/lib/music_library/record_sets.ex
+++ b/lib/music_library/record_sets.ex
@@ -6,6 +6,7 @@ defmodule MusicLibrary.RecordSets do
 
   @pagination Application.compile_env!(:music_library, :pagination)
 
+  @spec list_record_sets(MusicLibrary.Types.pagination_opts()) :: [RecordSet.t()]
   def list_record_sets(opts \\ []) do
     offset = Keyword.get(opts, :offset, 0)
     limit = Keyword.get(opts, :limit, @pagination[:default_page_size])
@@ -19,15 +20,18 @@ defmodule MusicLibrary.RecordSets do
     |> Repo.all()
   end
 
+  @spec count_record_sets() :: non_neg_integer()
   def count_record_sets do
     Repo.aggregate(RecordSet, :count)
   end
 
+  @spec count_record_sets(String.t()) :: non_neg_integer()
   def count_record_sets(query) do
     record_sets_search_query(query)
     |> Repo.aggregate(:count)
   end
 
+  @spec search_record_sets(String.t(), MusicLibrary.Types.pagination_opts()) :: [RecordSet.t()]
   def search_record_sets(query, opts \\ []) do
     offset = Keyword.get(opts, :offset, 0)
     limit = Keyword.get(opts, :limit, @pagination[:default_page_size])
@@ -49,12 +53,14 @@ defmodule MusicLibrary.RecordSets do
     order_by(query, [rs], desc: rs.updated_at)
   end
 
+  @spec get_record_set!(String.t()) :: RecordSet.t()
   def get_record_set!(id) do
     RecordSet
     |> Repo.get!(id)
     |> Repo.preload(items: :record)
   end
 
+  @spec create_record_set(map()) :: {:ok, RecordSet.t()} | {:error, Ecto.Changeset.t()}
   def create_record_set(attrs) do
     %RecordSet{}
     |> RecordSet.changeset(attrs)
@@ -65,6 +71,8 @@ defmodule MusicLibrary.RecordSets do
     end
   end
 
+  @spec update_record_set(RecordSet.t(), map()) ::
+          {:ok, RecordSet.t()} | {:error, Ecto.Changeset.t()}
   def update_record_set(%RecordSet{} = record_set, attrs) do
     record_set
     |> RecordSet.changeset(attrs)
@@ -75,14 +83,18 @@ defmodule MusicLibrary.RecordSets do
     end
   end
 
+  @spec delete_record_set(RecordSet.t()) :: {:ok, RecordSet.t()} | {:error, Ecto.Changeset.t()}
   def delete_record_set(%RecordSet{} = record_set) do
     Repo.delete(record_set)
   end
 
+  @spec change_record_set(RecordSet.t(), map()) :: Ecto.Changeset.t()
   def change_record_set(%RecordSet{} = record_set, attrs \\ %{}) do
     RecordSet.changeset(record_set, attrs)
   end
 
+  @spec add_record_to_set(RecordSet.t(), String.t()) ::
+          {:ok, RecordSet.t()} | {:error, Ecto.Changeset.t()}
   def add_record_to_set(%RecordSet{} = record_set, record_id) do
     next_position =
       from(i in RecordSetItem,
@@ -104,6 +116,7 @@ defmodule MusicLibrary.RecordSets do
     end
   end
 
+  @spec remove_record_from_set(RecordSet.t(), String.t()) :: {:ok, RecordSet.t()}
   def remove_record_from_set(%RecordSet{} = record_set, record_id) do
     item =
       from(i in RecordSetItem,
@@ -118,6 +131,7 @@ defmodule MusicLibrary.RecordSets do
     {:ok, get_record_set!(record_set.id)}
   end
 
+  @spec reorder_records_in_set(RecordSet.t(), [String.t()]) :: {:ok, RecordSet.t()}
   def reorder_records_in_set(%RecordSet{} = record_set, ordered_record_ids)
       when is_list(ordered_record_ids) do
     Repo.transaction(fn ->
@@ -134,6 +148,7 @@ defmodule MusicLibrary.RecordSets do
     {:ok, get_record_set!(record_set.id)}
   end
 
+  @spec move_record_in_set(RecordSet.t(), String.t(), :up | :down) :: {:ok, RecordSet.t()}
   def move_record_in_set(%RecordSet{} = record_set, record_id, direction)
       when direction in [:up, :down] do
     items =
@@ -169,6 +184,7 @@ defmodule MusicLibrary.RecordSets do
     {:ok, get_record_set!(record_set.id)}
   end
 
+  @spec list_record_sets_for_record(String.t()) :: [RecordSet.t()]
   def list_record_sets_for_record(record_id) do
     from(rs in RecordSet,
       join: i in RecordSetItem,
diff --git a/lib/music_library/record_sets/record_set.ex b/lib/music_library/record_sets/record_set.ex
index 0f162628..8098200d 100644
--- a/lib/music_library/record_sets/record_set.ex
+++ b/lib/music_library/record_sets/record_set.ex
@@ -16,6 +16,9 @@ defmodule MusicLibrary.RecordSets.RecordSet do
     timestamps(type: :utc_datetime)
   end
 
+  @type t :: %__MODULE__{}
+
+  @spec changeset(t() | Ecto.Changeset.t(), map()) :: Ecto.Changeset.t()
   def changeset(record_set, attrs) do
     record_set
     |> cast(attrs, [:name, :description])
@@ -24,6 +27,11 @@ defmodule MusicLibrary.RecordSets.RecordSet do
     |> validate_length(:description, max: 10_000)
   end
 
+  @spec count_by_status(t()) :: %{
+          collected: non_neg_integer(),
+          wishlisted: non_neg_integer(),
+          total: non_neg_integer()
+        }
   def count_by_status(record_set) do
     record_set.items
     |> Enum.frequencies_by(fn item ->
diff --git a/lib/music_library/record_sets/record_set_item.ex b/lib/music_library/record_sets/record_set_item.ex
index 9dbb3ebf..a317a687 100644
--- a/lib/music_library/record_sets/record_set_item.ex
+++ b/lib/music_library/record_sets/record_set_item.ex
@@ -17,6 +17,9 @@ defmodule MusicLibrary.RecordSets.RecordSetItem do
     timestamps(type: :utc_datetime)
   end
 
+  @type t :: %__MODULE__{}
+
+  @spec changeset(t() | Ecto.Changeset.t(), map()) :: Ecto.Changeset.t()
   def changeset(record_set_item, attrs) do
     record_set_item
     |> cast(attrs, [:position])
diff --git a/lib/music_library/records.ex b/lib/music_library/records.ex
index 98ce3571..65366d9f 100644
--- a/lib/music_library/records.ex
+++ b/lib/music_library/records.ex
@@ -11,10 +11,19 @@ defmodule MusicLibrary.Records do
   alias MusicLibrary.Records.{ArtistRecord, Record, SearchIndex, SearchParser}
   alias MusicLibrary.{Repo, Worker}
 
+  @type import_opts :: [
+          format: atom(),
+          purchased_at: DateTime.t() | nil,
+          selected_release_id: String.t() | nil
+        ]
+
+  @spec essential_fields() :: [atom()]
   def essential_fields do
     SearchIndex.__schema__(:fields)
   end
 
+  @spec search_records(Ecto.Queryable.t(), String.t(), MusicLibrary.Types.pagination_opts()) ::
+          [SearchIndex.t()]
   def search_records(initial_search, query, opts) do
     limit = Keyword.fetch!(opts, :limit)
     offset = Keyword.fetch!(opts, :offset)
@@ -30,6 +39,7 @@ defmodule MusicLibrary.Records do
     Repo.all(search)
   end
 
+  @spec search_records_count(Ecto.Queryable.t(), String.t()) :: non_neg_integer()
   def search_records_count(initial_search, query) do
     search = build_search(initial_search, query)
 
@@ -158,6 +168,7 @@ defmodule MusicLibrary.Records do
     end)
   end
 
+  @spec list_genres() :: [String.t()]
   def list_genres do
     q =
       from r in fragment("records, json_each(records.genres)"),
@@ -167,8 +178,11 @@ defmodule MusicLibrary.Records do
     Repo.all(q)
   end
 
+  @spec get_record!(String.t()) :: Record.t()
   def get_record!(id), do: Repo.get!(Record, id)
 
+  @spec get_release_status(String.t(), String.t()) ::
+          :new | {:wishlisted, String.t()} | {:collected, String.t()}
   def get_release_status(release_id, format) do
     q =
       from r in fragment("records, json_each(records.release_ids)"),
@@ -185,6 +199,7 @@ defmodule MusicLibrary.Records do
     end
   end
 
+  @spec get_artist_records(String.t()) :: [SearchIndex.t()]
   def get_artist_records(musicbrainz_id) do
     q =
       from r in Record,
@@ -195,6 +210,8 @@ defmodule MusicLibrary.Records do
     Repo.all(q)
   end
 
+  @spec import_from_musicbrainz_release(String.t(), import_opts()) ::
+          {:ok, Record.t()} | {:error, term()}
   def import_from_musicbrainz_release(musicbrainz_id, opts \\ []) do
     case MusicBrainz.get_release(musicbrainz_id) do
       {:ok, release} ->
@@ -206,6 +223,8 @@ defmodule MusicLibrary.Records do
     end
   end
 
+  @spec import_from_musicbrainz_release_group(String.t(), import_opts()) ::
+          {:ok, Record.t()} | {:error, term()}
   def import_from_musicbrainz_release_group(musicbrainz_id, opts \\ []) do
     format = Keyword.get(opts, :format, "cd")
     purchased_at = Keyword.get(opts, :purchased_at)
@@ -226,6 +245,7 @@ defmodule MusicLibrary.Records do
     end
   end
 
+  @spec populate_genres(Record.t()) :: {:ok, Record.t()} | {:error, Ecto.Changeset.t()}
   def populate_genres(record) do
     artists = Enum.map_join(record.artists, ",", fn a -> a.name end)
 
@@ -246,6 +266,7 @@ defmodule MusicLibrary.Records do
     |> Repo.update()
   end
 
+  @spec populate_genres_async(Record.t()) :: {:ok, Oban.Job.t()} | {:error, Ecto.Changeset.t()}
   def populate_genres_async(record) do
     enqueue_worker(Worker.PopulateGenres, %{"id" => record.id}, record_meta(record))
   end
@@ -257,6 +278,7 @@ defmodule MusicLibrary.Records do
     end
   end
 
+  @spec get_last_listened_track(Record.t()) :: LastFm.Track.t() | nil
   def get_last_listened_track(record) do
     q =
       from t in scrobbles_for_record_query(record),
@@ -266,6 +288,7 @@ defmodule MusicLibrary.Records do
     Repo.one(q)
   end
 
+  @spec play_count(Record.t()) :: non_neg_integer()
   def play_count(record) do
     record
     |> scrobbles_for_record_query()
@@ -291,6 +314,7 @@ defmodule MusicLibrary.Records do
           fragment("? ->> '$.name'", t.artist) == ^main_artist_name
   end
 
+  @spec refresh_cover(Record.t()) :: {:ok, Record.t()} | {:error, term()}
   def refresh_cover(record) do
     with {:ok, cover_data} <- MusicBrainz.get_cover_art({:url, record.cover_url}),
          {:ok, thumb_data} <- Assets.Image.resize(cover_data),
@@ -301,10 +325,12 @@ defmodule MusicLibrary.Records do
     end
   end
 
+  @spec refresh_cover_async(Record.t()) :: {:ok, Oban.Job.t()} | {:error, Ecto.Changeset.t()}
   def refresh_cover_async(record) do
     enqueue_worker(Worker.RefreshCover, %{"id" => record.id}, record_meta(record))
   end
 
+  @spec extract_colors(Record.t()) :: {:ok, Record.t()} | {:error, term()}
   def extract_colors(record) do
     asset = Assets.get!(record.cover_hash)
 
@@ -313,6 +339,8 @@ defmodule MusicLibrary.Records do
     end
   end
 
+  @spec generate_embedding_async(Record.t()) ::
+          {:ok, Oban.Job.t()} | {:error, Ecto.Changeset.t()}
   def generate_embedding_async(record) do
     enqueue_worker(
       Worker.GenerateRecordEmbedding,
@@ -321,6 +349,7 @@ defmodule MusicLibrary.Records do
     )
   end
 
+  @spec resize_cover(Record.t()) :: {:ok, Record.t()} | {:error, term()}
   def resize_cover(record) do
     with {:ok, thumb_data} <- Assets.Image.resize(record.cover_data),
          {:ok, asset} <- Assets.store_image(%{content: thumb_data, format: "image/jpeg"}) do
@@ -330,6 +359,7 @@ defmodule MusicLibrary.Records do
     end
   end
 
+  @spec refresh_musicbrainz_data(Record.t()) :: {:ok, Record.t()} | {:error, term()}
   def refresh_musicbrainz_data(record) do
     with {:ok, data} <- MusicBrainz.get_release_group(record.musicbrainz_id),
          {:ok, data_with_releases} <- merge_releases(record.musicbrainz_id, data) do
@@ -339,6 +369,8 @@ defmodule MusicLibrary.Records do
     end
   end
 
+  @spec refresh_musicbrainz_data_async(Record.t()) ::
+          {:ok, Oban.Job.t()} | {:error, Ecto.Changeset.t()}
   def refresh_musicbrainz_data_async(record) do
     enqueue_worker(Worker.RecordRefreshMusicBrainzData, %{"id" => record.id}, record_meta(record))
   end
@@ -374,6 +406,7 @@ defmodule MusicLibrary.Records do
     |> Map.merge(attrs)
   end
 
+  @spec create_record(map()) :: {:ok, Record.t()} | {:error, Ecto.Changeset.t()}
   def create_record(attrs \\ %{}) do
     with {:ok, record} <- do_create_record(attrs) do
       {:ok, record} = extract_colors(record)
@@ -395,12 +428,14 @@ defmodule MusicLibrary.Records do
     |> Repo.insert()
   end
 
+  @spec update_record(Record.t(), map()) :: {:ok, Record.t()} | {:error, Ecto.Changeset.t()}
   def update_record(%Record{} = record, attrs) do
     record
     |> Record.changeset(attrs)
     |> Repo.update()
   end
 
+  @spec delete_record(Record.t()) :: {:ok, Record.t()} | {:error, Ecto.Changeset.t()}
   def delete_record(%Record{} = record) do
     with {:ok, record} <- Repo.delete(record) do
       record
@@ -413,14 +448,17 @@ defmodule MusicLibrary.Records do
     end
   end
 
+  @spec change_record(Record.t(), map()) :: Ecto.Changeset.t()
   def change_record(%Record{} = record, attrs \\ %{}) do
     Record.changeset(record, attrs)
   end
 
+  @spec subscribe(String.t()) :: :ok | {:error, term()}
   def subscribe(record_id) do
     Phoenix.PubSub.subscribe(MusicLibrary.PubSub, "records:#{record_id}")
   end
 
+  @spec notify_update(Record.t()) :: :ok | {:error, term()}
   def notify_update(record) do
     Phoenix.PubSub.broadcast(
       MusicLibrary.PubSub,
diff --git a/lib/music_library/records/artist_records.ex b/lib/music_library/records/artist_records.ex
index e3b423ed..06ea7593 100644
--- a/lib/music_library/records/artist_records.ex
+++ b/lib/music_library/records/artist_records.ex
@@ -16,4 +16,6 @@ defmodule MusicLibrary.Records.ArtistRecord do
 
     embeds_one :artist, Artist
   end
+
+  @type t :: %__MODULE__{}
 end
diff --git a/lib/music_library/records/batch.ex b/lib/music_library/records/batch.ex
index fbb59a3e..82cceef8 100644
--- a/lib/music_library/records/batch.ex
+++ b/lib/music_library/records/batch.ex
@@ -5,12 +5,14 @@ defmodule MusicLibrary.Records.Batch do
   alias MusicLibrary.Records
   alias MusicLibrary.Records.Record
 
+  @spec refresh_musicbrainz_data() :: {:ok, [String.t()]}
   def refresh_musicbrainz_data do
     Batch.run_on_all(from(r in Record), "record", fn record ->
       Records.refresh_musicbrainz_data_async(record)
     end)
   end
 
+  @spec generate_embeddings() :: {:ok, [String.t()]}
   def generate_embeddings do
     Batch.run_on_all(from(r in Record), "record", fn record ->
       Records.generate_embedding_async(record)
diff --git a/lib/music_library/records/record.ex b/lib/music_library/records/record.ex
index 28bcee77..ff0f9a06 100644
--- a/lib/music_library/records/record.ex
+++ b/lib/music_library/records/record.ex
@@ -33,10 +33,14 @@ defmodule MusicLibrary.Records.Record do
     timestamps(type: :utc_datetime)
   end
 
+  @type t :: %__MODULE__{}
+
+  @spec artist_names(t()) :: String.t()
   def artist_names(record) do
     Enum.map_join(record.artists, ", ", fn artist -> artist.name end)
   end
 
+  @spec main_artist(t()) :: Artist.t() | nil
   def main_artist(record) do
     case record.artists do
       [] -> nil
@@ -44,27 +48,35 @@ defmodule MusicLibrary.Records.Record do
     end
   end
 
+  @spec artist_ids(t()) :: [String.t()]
   def artist_ids(record) do
     Enum.map(record.artists, fn artist -> artist.musicbrainz_id end)
   end
 
+  @spec formats() :: [atom()]
   def formats, do: @formats
+
+  @spec types() :: [atom()]
   def types, do: @types
 
+  @spec included_release_groups(t()) :: [map()]
   def included_release_groups(record) do
     record.musicbrainz_data
     |> ReleaseGroup.included_release_groups()
     |> Enum.filter(fn rg -> rg.id in record.included_release_group_ids end)
   end
 
+  @spec included_release_groups_count(t()) :: non_neg_integer()
   def included_release_groups_count(record) do
     Enum.count(record.included_release_group_ids)
   end
 
+  @spec release_count(t()) :: non_neg_integer()
   def release_count(record) do
     Enum.count(record.release_ids)
   end
 
+  @spec released?(t(), Date.t()) :: boolean()
   def released?(%{release_date: nil}, _current_day), do: true
 
   def released?(record, current_day) do
@@ -80,6 +92,7 @@ defmodule MusicLibrary.Records.Record do
     end
   end
 
+  @spec released_how_long_ago?(t(), Date.t()) :: non_neg_integer() | nil
   def released_how_long_ago?(%{release_date: nil}, _current_day), do: nil
 
   def released_how_long_ago?(record, current_day) do
@@ -95,6 +108,7 @@ defmodule MusicLibrary.Records.Record do
     end
   end
 
+  @spec releases(t()) :: [MusicBrainz.Release.t()]
   def releases(record) do
     record.musicbrainz_data
     |> ReleaseGroup.releases()
@@ -102,16 +116,19 @@ defmodule MusicLibrary.Records.Record do
     |> Enum.sort_by(fn r -> {r.date, r.country} end, :desc)
   end
 
+  @spec selected_release(t()) :: MusicBrainz.Release.t() | nil
   def selected_release(record) do
     find_release(record, record.selected_release_id)
   end
 
+  @spec find_release(t(), String.t() | nil) :: MusicBrainz.Release.t() | nil
   def find_release(record, release_id) do
     record
     |> releases()
     |> Enum.find(fn release -> release.id == release_id end)
   end
 
+  @spec changeset(t() | Ecto.Changeset.t(), map()) :: Ecto.Changeset.t()
   def changeset(record, attrs) do
     record
     |> cast(attrs, [
@@ -137,15 +154,18 @@ defmodule MusicLibrary.Records.Record do
     |> update_included_release_group_ids()
   end
 
+  @spec add_genres(t(), [String.t()]) :: Ecto.Changeset.t()
   def add_genres(record, genres) do
     change(record, genres: genres)
   end
 
+  @spec set_cover_hash(t(), String.t()) :: Ecto.Changeset.t()
   def set_cover_hash(record, cover_hash) do
     record
     |> change(cover_hash: cover_hash)
   end
 
+  @spec add_musicbrainz_data(t(), map()) :: Ecto.Changeset.t()
   def add_musicbrainz_data(record, musicbrainz_data) do
     record
     |> change()
@@ -156,6 +176,7 @@ defmodule MusicLibrary.Records.Record do
     |> update_musicbrainz_data_derived_fields()
   end
 
+  @spec rotate_dominant_colors(t() | Ecto.Changeset.t()) :: Ecto.Changeset.t()
   def rotate_dominant_colors(%__MODULE__{dominant_colors: dominant_colors} = record) do
     change(record, dominant_colors: rotate(dominant_colors))
   end
@@ -218,6 +239,7 @@ defmodule MusicLibrary.Records.Record do
     end
   end
 
+  @spec attrs_from_release_group(map()) :: map()
   def attrs_from_release_group(release_group) do
     musicbrainz_id = release_group["id"]
 
@@ -293,6 +315,7 @@ defmodule MusicLibrary.Records.Record do
     end
   end
 
+  @spec format_as_date(DateTime.t() | NaiveDateTime.t() | Date.t()) :: String.t()
   def format_as_date(dt) do
     Calendar.strftime(dt, "%d/%m/%Y")
   end
diff --git a/lib/music_library/records/record_embedding.ex b/lib/music_library/records/record_embedding.ex
index dd5a608a..a01456ce 100644
--- a/lib/music_library/records/record_embedding.ex
+++ b/lib/music_library/records/record_embedding.ex
@@ -16,6 +16,9 @@ defmodule MusicLibrary.Records.RecordEmbedding do
     timestamps(type: :utc_datetime)
   end
 
+  @type t :: %__MODULE__{}
+
+  @spec changeset(t() | Ecto.Changeset.t(), map()) :: Ecto.Changeset.t()
   def changeset(record_embedding, attrs) do
     record_embedding
     |> cast(attrs, [:record_id, :embedding, :text_representation])
diff --git a/lib/music_library/records/record_release.ex b/lib/music_library/records/record_release.ex
index f6d7a71a..09ca84a2 100644
--- a/lib/music_library/records/record_release.ex
+++ b/lib/music_library/records/record_release.ex
@@ -8,4 +8,6 @@ defmodule MusicLibrary.Records.RecordRelease do
     field :cover_hash, :string
     field :purchased_at, :utc_datetime
   end
+
+  @type t :: %__MODULE__{}
 end
diff --git a/lib/music_library/records/search_index.ex b/lib/music_library/records/search_index.ex
index 0047621d..b100b187 100644
--- a/lib/music_library/records/search_index.ex
+++ b/lib/music_library/records/search_index.ex
@@ -31,4 +31,6 @@ defmodule MusicLibrary.Records.SearchIndex do
 
     timestamps(type: :utc_datetime)
   end
+
+  @type t :: %__MODULE__{}
 end
diff --git a/lib/music_library/records/search_parser.ex b/lib/music_library/records/search_parser.ex
index c7ae1dc9..36f29189 100644
--- a/lib/music_library/records/search_parser.ex
+++ b/lib/music_library/records/search_parser.ex
@@ -7,6 +7,17 @@ defmodule MusicLibrary.Records.SearchParser do
   edge cases I haven't thought about - not an expert in parsing.
   """
 
+  @type search_result :: %{
+          optional(:query) => String.t(),
+          optional(:artist) => String.t(),
+          optional(:album) => String.t(),
+          optional(:mbid) => String.t(),
+          optional(:genre) => String.t(),
+          optional(:format) => atom(),
+          optional(:type) => atom(),
+          optional(:purchase_year) => integer()
+        }
+
   import NimbleParsec
 
   word = utf8_string([not: ?\s, not: ?,], min: 1)
@@ -99,6 +110,7 @@ defmodule MusicLibrary.Records.SearchParser do
     iex> MusicLibrary.Records.SearchParser.parse("purchase_year:2024")
     {:ok, %{purchase_year: 2024}}
   """
+  @spec parse(String.t()) :: {:ok, search_result()}
   def parse(""), do: {:ok, %{query: ""}}
 
   def parse(query) do
@@ -107,11 +119,13 @@ defmodule MusicLibrary.Records.SearchParser do
     {:ok, normalize(result)}
   end
 
+  @spec resolve_format(String.t()) :: atom() | nil
   def resolve_format(format) do
     Ecto.Enum.mappings(MusicLibrary.Records.Record, :format)
     |> Enum.find_value(fn {key, value} -> if value == format, do: key end)
   end
 
+  @spec resolve_type(String.t()) :: atom() | nil
   def resolve_type(type) do
     Ecto.Enum.mappings(MusicLibrary.Records.Record, :type)
     |> Enum.find_value(fn {key, value} -> if value == type, do: key end)
diff --git a/lib/music_library/records/similarity.ex b/lib/music_library/records/similarity.ex
index 8960abf5..ba2701a3 100644
--- a/lib/music_library/records/similarity.ex
+++ b/lib/music_library/records/similarity.ex
@@ -16,6 +16,12 @@ defmodule MusicLibrary.Records.Similarity do
 
   @max_distance Application.compile_env!(:music_library, :similarity)[:max_distance]
 
+  @type find_opts :: [
+          limit: pos_integer(),
+          scope: :collection | :wishlist | nil,
+          max_distance: float()
+        ]
+
   @doc """
   Generates a text representation of a record for embedding generation.
 
@@ -30,6 +36,7 @@ defmodule MusicLibrary.Records.Similarity do
   - Last.fm community tags and similar artists (when stored)
   - User-written record notes (when present)
   """
+  @spec text_representation(Record.t()) :: String.t()
   def text_representation(%Record{} = record) do
     artist_infos_map =
       record.artists
@@ -231,13 +238,6 @@ defmodule MusicLibrary.Records.Similarity do
   @doc """
   Finds similar records based on embedding similarity.
 
-  ## Options
-
-  - `:limit` - Maximum number of similar records to return (default: 10)
-  - `:scope` - Filter by :collection or :wishlist (default: no filter)
-  - `:max_distance` - Maximum cosine distance threshold (default: #{@max_distance}).
-    Results with distance above this are excluded.
-
   ## Examples
 
       iex> find_similar("record-id-123", limit: 5)
@@ -246,6 +246,7 @@ defmodule MusicLibrary.Records.Similarity do
       iex> find_similar("record-id-123", scope: :collection)
       [%Record{}, ...]
   """
+  @spec find_similar(String.t(), find_opts()) :: [map()]
   def find_similar(record_id, opts \\ []) do
     limit = Keyword.get(opts, :limit, 10)
     scope = Keyword.get(opts, :scope)
@@ -282,9 +283,7 @@ defmodule MusicLibrary.Records.Similarity do
     end
   end
 
-  @doc """
-  Gets the embedding for a record.
-  """
+  @spec get_embedding(String.t()) :: {:ok, binary()} | {:error, :not_found}
   def get_embedding(record_id) do
     case Repo.get_by(RecordEmbedding, record_id: record_id) do
       nil -> {:error, :not_found}
@@ -292,6 +291,7 @@ defmodule MusicLibrary.Records.Similarity do
     end
   end
 
+  @spec get_embedding_text(String.t()) :: {:ok, String.t()} | {:error, :not_found}
   def get_embedding_text(record_id) do
     case Repo.get_by(RecordEmbedding, record_id: record_id) do
       nil -> {:error, :not_found}
@@ -299,9 +299,8 @@ defmodule MusicLibrary.Records.Similarity do
     end
   end
 
-  @doc """
-  Stores an embedding for a record.
-  """
+  @spec store_embedding(String.t(), binary(), String.t()) ::
+          {:ok, RecordEmbedding.t()} | {:error, Ecto.Changeset.t()}
   def store_embedding(record_id, embedding, text_representation) do
     attrs = %{
       record_id: record_id,
@@ -317,6 +316,7 @@ defmodule MusicLibrary.Records.Similarity do
     )
   end
 
+  @spec generate_embedding_async(Record.t()) :: {:ok, Oban.Job.t()} | {:error, Ecto.Changeset.t()}
   def generate_embedding_async(record) do
     meta = %{title: record.title, artists: Enum.map(record.artists, & &1.name)}
     params = %{record_id: record.id}
@@ -326,6 +326,7 @@ defmodule MusicLibrary.Records.Similarity do
     |> Oban.insert()
   end
 
+  @spec generate_all_embeddings_async() :: non_neg_integer()
   def generate_all_embeddings_async do
     Record
     |> Repo.all()
diff --git a/lib/music_library/scrobble_activity.ex b/lib/music_library/scrobble_activity.ex
index c4884372..aec67132 100644
--- a/lib/music_library/scrobble_activity.ex
+++ b/lib/music_library/scrobble_activity.ex
@@ -7,10 +7,12 @@ defmodule MusicLibrary.ScrobbleActivity do
 
   @pagination Application.compile_env!(:music_library, :pagination)
 
+  @spec can_scrobble?() :: boolean()
   def can_scrobble? do
     Secrets.get("last_fm_session_key") !== nil
   end
 
+  @spec scrobble_release(map(), keyword()) :: {:ok, term()} | {:error, term()}
   def scrobble_release(release_with_tracks, opts) when is_list(opts) do
     case Enum.sort(opts) do
       [finished_at: _, started_at: _] ->
@@ -27,12 +29,14 @@ defmodule MusicLibrary.ScrobbleActivity do
     end
   end
 
+  @spec scrobble_release(map(), {:finished_at, DateTime.t()}) :: {:ok, term()} | {:error, term()}
   def scrobble_release(release_with_tracks, {:finished_at, finished_at}) do
     release_duration = Release.release_duration(release_with_tracks)
     started_at = DateTime.add(finished_at, -release_duration, :millisecond)
     scrobble_release(release_with_tracks, {:started_at, started_at})
   end
 
+  @spec scrobble_release(map(), {:started_at, DateTime.t()}) :: {:ok, term()} | {:error, term()}
   def scrobble_release(release_with_tracks, {:started_at, started_at}) do
     release_duration = Release.release_duration(release_with_tracks)
 
@@ -50,6 +54,7 @@ defmodule MusicLibrary.ScrobbleActivity do
     end
   end
 
+  @spec scrobble_medium(integer(), map(), keyword()) :: {:ok, term()} | {:error, term()}
   def scrobble_medium(number, release_with_tracks, opts) when is_list(opts) do
     case Enum.sort(opts) do
       [finished_at: _, started_at: _] ->
@@ -66,6 +71,8 @@ defmodule MusicLibrary.ScrobbleActivity do
     end
   end
 
+  @spec scrobble_medium(integer(), map(), {:finished_at, DateTime.t()}) ::
+          {:ok, term()} | {:error, term()}
   def scrobble_medium(number, release_with_tracks, {:finished_at, finished_at}) do
     case find_medium(release_with_tracks, number) do
       {:ok, medium} ->
@@ -78,6 +85,8 @@ defmodule MusicLibrary.ScrobbleActivity do
     end
   end
 
+  @spec scrobble_medium(integer(), map(), {:started_at, DateTime.t()}) ::
+          {:ok, term()} | {:error, term()}
   def scrobble_medium(number, release_with_tracks, {:started_at, started_at}) do
     case find_medium(release_with_tracks, number) do
       {:ok, medium} ->
@@ -100,6 +109,7 @@ defmodule MusicLibrary.ScrobbleActivity do
     end
   end
 
+  @spec scrobble_tracks(MapSet.t(), map(), keyword()) :: {:ok, term()} | {:error, term()}
   def scrobble_tracks(selected_track_ids, release_with_tracks, opts) when is_list(opts) do
     case Enum.sort(opts) do
       [finished_at: _, started_at: _] ->
@@ -116,6 +126,8 @@ defmodule MusicLibrary.ScrobbleActivity do
     end
   end
 
+  @spec scrobble_tracks(MapSet.t(), map(), {:finished_at, DateTime.t()}) ::
+          {:ok, term()} | {:error, term()}
   def scrobble_tracks(selected_track_ids, release_with_tracks, {:finished_at, finished_at}) do
     all_tracks = Release.tracks(release_with_tracks)
 
@@ -127,6 +139,8 @@ defmodule MusicLibrary.ScrobbleActivity do
     scrobble_tracks(selected_track_ids, release_with_tracks, {:started_at, started_at})
   end
 
+  @spec scrobble_tracks(MapSet.t(), map(), {:started_at, DateTime.t()}) ::
+          {:ok, term()} | {:error, term()}
   def scrobble_tracks(selected_track_ids, release_with_tracks, {:started_at, started_at}) do
     all_tracks = Release.tracks(release_with_tracks)
 
@@ -187,9 +201,7 @@ defmodule MusicLibrary.ScrobbleActivity do
   defp main_artist_name([]), do: nil
   defp main_artist_name([artist | _rest]), do: artist.name
 
-  @doc """
-  Lists scrobbled tracks with pagination and search support.
-  """
+  @spec list_tracks(map()) :: [map()]
   def list_tracks(params \\ %{}) do
     query = Map.get(params, :query, "")
     page = Map.get(params, :page, 1)
@@ -250,23 +262,12 @@ defmodule MusicLibrary.ScrobbleActivity do
     |> Repo.all()
   end
 
-  @doc """
-  Returns the total number of scrobbled tracks.
-
-  This counts all tracks stored in the database using their `scrobbled_at_uts` as the primary key.
-
-  ## Examples
-
-      iex> MusicLibrary.ScrobbleActivity.count_tracks()
-      42
-  """
+  @spec count_tracks() :: non_neg_integer()
   def count_tracks do
     Repo.aggregate(Track, :count, :scrobbled_at_uts)
   end
 
-  @doc """
-  Gets a single track by scrobbled_at_uts.
-  """
+  @spec get_track!(integer() | String.t()) :: LastFm.Track.t()
   def get_track!(scrobbled_at_uts) when is_integer(scrobbled_at_uts) do
     Repo.get!(Track, scrobbled_at_uts)
   end
@@ -278,24 +279,19 @@ defmodule MusicLibrary.ScrobbleActivity do
     end
   end
 
-  @doc """
-  Updates a track with the given attributes.
-  """
+  @spec update_track(LastFm.Track.t(), map()) ::
+          {:ok, LastFm.Track.t()} | {:error, Ecto.Changeset.t()}
   def update_track(%Track{} = track, attrs) do
     changeset = Track.changeset(track, attrs)
     Repo.update(changeset)
   end
 
-  @doc """
-  Deletes a track.
-  """
+  @spec delete_track(LastFm.Track.t()) :: {:ok, LastFm.Track.t()} | {:error, Ecto.Changeset.t()}
   def delete_track(%Track{} = track) do
     Repo.delete(track)
   end
 
-  @doc """
-  Counts tracks matching the search query.
-  """
+  @spec search_tracks_count(String.t()) :: non_neg_integer()
   def search_tracks_count(query \\ "") do
     base_query = from(t in Track)
 
@@ -315,15 +311,7 @@ defmodule MusicLibrary.ScrobbleActivity do
     Repo.aggregate(search_query, :count, :scrobbled_at_uts)
   end
 
-  @doc """
-  Counts tracks with missing or empty artist MusicBrainz IDs.
-
-  ## Examples
-
-      iex> count_tracks_missing_artist_musicbrainz_id()
-      42
-
-  """
+  @spec count_tracks_missing_artist_musicbrainz_id() :: non_neg_integer()
   def count_tracks_missing_artist_musicbrainz_id do
     query =
       from t in Track,
@@ -335,15 +323,7 @@ defmodule MusicLibrary.ScrobbleActivity do
     Repo.one(query) || 0
   end
 
-  @doc """
-  Counts tracks with missing or empty album MusicBrainz IDs.
-
-  ## Examples
-
-      iex> count_tracks_missing_album_musicbrainz_id()
-      37
-
-  """
+  @spec count_tracks_missing_album_musicbrainz_id() :: non_neg_integer()
   def count_tracks_missing_album_musicbrainz_id do
     query =
       from t in Track,
@@ -359,13 +339,8 @@ defmodule MusicLibrary.ScrobbleActivity do
   Gets artists with missing MusicBrainz IDs, grouped by artist name.
 
   Returns a list of maps with artist name and track count.
-
-  ## Examples
-
-      iex> get_artists_missing_musicbrainz_id()
-      [%{artist_name: "Some Artist", track_count: 5}, ...]
-
   """
+  @spec get_artists_missing_musicbrainz_id(keyword()) :: [map()]
   def get_artists_missing_musicbrainz_id(opts \\ []) do
     limit = Keyword.get(opts, :limit)
 
@@ -395,13 +370,8 @@ defmodule MusicLibrary.ScrobbleActivity do
   Gets albums with missing MusicBrainz IDs, grouped by album title and artist.
 
   Returns a list of maps with album title, artist name, and track count.
-
-  ## Examples
-
-      iex> get_albums_missing_musicbrainz_id()
-      [%{album_title: "Some Album", artist_name: "Some Artist", track_count: 3}, ...]
-
   """
+  @spec get_albums_missing_musicbrainz_id(keyword()) :: [map()]
   def get_albums_missing_musicbrainz_id(opts \\ []) do
     limit = Keyword.get(opts, :limit)
 
diff --git a/lib/music_library/scrobble_rules.ex b/lib/music_library/scrobble_rules.ex
index 9fcea112..fbcb9ea1 100644
--- a/lib/music_library/scrobble_rules.ex
+++ b/lib/music_library/scrobble_rules.ex
@@ -11,15 +11,14 @@ defmodule MusicLibrary.ScrobbleRules do
   alias MusicLibrary.Repo
   alias MusicLibrary.ScrobbleRules.ScrobbleRule
 
-  @doc """
-  Returns the list of scrobble_rules.
+  @type list_opts :: [
+          type: atom(),
+          enabled: boolean(),
+          offset: non_neg_integer(),
+          limit: non_neg_integer()
+        ]
 
-  ## Examples
-
-      iex> list_scrobble_rules()
-      [%ScrobbleRule{}, ...]
-
-  """
+  @spec list_scrobble_rules(list_opts()) :: [ScrobbleRule.t()]
   def list_scrobble_rules(opts \\ []) do
     query =
       from r in ScrobbleRule,
@@ -68,15 +67,7 @@ defmodule MusicLibrary.ScrobbleRules do
     Repo.all(query)
   end
 
-  @doc """
-  Returns the count of scrobble_rules.
-
-  ## Examples
-
-      iex> count_scrobble_rules()
-      42
-
-  """
+  @spec count_scrobble_rules(list_opts()) :: non_neg_integer()
   def count_scrobble_rules(opts \\ []) do
     query = from(r in ScrobbleRule)
 
@@ -103,112 +94,41 @@ defmodule MusicLibrary.ScrobbleRules do
     Repo.aggregate(query, :count)
   end
 
-  @doc """
-  Gets a single scrobble_rule.
-
-  Raises `Ecto.NoResultsError` if the Scrobble rule does not exist.
-
-  ## Examples
-
-      iex> get_scrobble_rule!(123)
-      %ScrobbleRule{}
-
-      iex> get_scrobble_rule!(456)
-      ** (Ecto.NoResultsError)
-
-  """
+  @spec get_scrobble_rule!(integer()) :: ScrobbleRule.t()
   def get_scrobble_rule!(id), do: Repo.get!(ScrobbleRule, id)
 
-  @doc """
-  Creates a scrobble_rule.
-
-  ## Examples
-
-      iex> create_scrobble_rule(%{field: value})
-      {:ok, %ScrobbleRule{}}
-
-      iex> create_scrobble_rule(%{field: bad_value})
-      {:error, %Ecto.Changeset{}}
-
-  """
+  @spec create_scrobble_rule(map()) :: {:ok, ScrobbleRule.t()} | {:error, Ecto.Changeset.t()}
   def create_scrobble_rule(attrs \\ %{}) do
     %ScrobbleRule{}
     |> ScrobbleRule.changeset(attrs)
     |> Repo.insert()
   end
 
-  @doc """
-  Updates a scrobble_rule.
-
-  ## Examples
-
-      iex> update_scrobble_rule(scrobble_rule, %{field: new_value})
-      {:ok, %ScrobbleRule{}}
-
-      iex> update_scrobble_rule(scrobble_rule, %{field: bad_value})
-      {:error, %Ecto.Changeset{}}
-
-  """
+  @spec update_scrobble_rule(ScrobbleRule.t(), map()) ::
+          {:ok, ScrobbleRule.t()} | {:error, Ecto.Changeset.t()}
   def update_scrobble_rule(%ScrobbleRule{} = scrobble_rule, attrs) do
     scrobble_rule
     |> ScrobbleRule.changeset(attrs)
     |> Repo.update()
   end
 
-  @doc """
-  Deletes a scrobble_rule.
-
-  ## Examples
-
-      iex> delete_scrobble_rule(scrobble_rule)
-      {:ok, %ScrobbleRule{}}
-
-      iex> delete_scrobble_rule(scrobble_rule)
-      {:error, %Ecto.Changeset{}}
-
-  """
+  @spec delete_scrobble_rule(ScrobbleRule.t()) ::
+          {:ok, ScrobbleRule.t()} | {:error, Ecto.Changeset.t()}
   def delete_scrobble_rule(%ScrobbleRule{} = scrobble_rule) do
     Repo.delete(scrobble_rule)
   end
 
-  @doc """
-  Returns an `%Ecto.Changeset{}` for tracking scrobble_rule changes.
-
-  ## Examples
-
-      iex> change_scrobble_rule(scrobble_rule)
-      %Ecto.Changeset{data: %ScrobbleRule{}}
-
-  """
+  @spec change_scrobble_rule(ScrobbleRule.t(), map()) :: Ecto.Changeset.t()
   def change_scrobble_rule(%ScrobbleRule{} = scrobble_rule, attrs \\ %{}) do
     ScrobbleRule.changeset(scrobble_rule, attrs)
   end
 
-  @doc """
-  Returns the list of enabled scrobble_rules.
-
-  ## Examples
-
-      iex> list_enabled_rules()
-      [%ScrobbleRule{}, ...]
-
-  """
+  @spec list_enabled_rules() :: [ScrobbleRule.t()]
   def list_enabled_rules do
     list_scrobble_rules(enabled: true)
   end
 
-  @doc """
-  Applies an album rule to all matching scrobbled tracks.
-
-  ## Examples
-
-      iex> apply_album_rule(rule)
-      {:ok, 5}
-
-      iex> apply_album_rule(rule)
-      {:error, :invalid_rule_type}
-
-  """
+  @spec apply_album_rule(ScrobbleRule.t()) :: {:ok, non_neg_integer()} | {:error, term()}
   def apply_album_rule(%ScrobbleRule{type: :album} = rule) do
     update_query =
       from(t in Track,
@@ -231,18 +151,8 @@ defmodule MusicLibrary.ScrobbleRules do
     end
   end
 
-  @doc """
-  Applies an album rule to a specific set of scrobbled tracks.
-
-  ## Examples
-
-      iex> apply_album_rule(rule, tracks)
-      {:ok, 3}
-
-      iex> apply_album_rule(rule, tracks)
-      {:error, :invalid_rule_type}
-
-  """
+  @spec apply_album_rule(ScrobbleRule.t(), [LastFm.Track.t()]) ::
+          {:ok, non_neg_integer()} | {:error, term()}
   def apply_album_rule(%ScrobbleRule{type: :album} = rule, tracks) do
     track_scrobbled_at_uts = Enum.map(tracks, & &1.scrobbled_at_uts)
 
@@ -269,18 +179,7 @@ defmodule MusicLibrary.ScrobbleRules do
     end
   end
 
-  @doc """
-  Applies an artist rule to all matching scrobbled tracks.
-
-  ## Examples
-
-      iex> apply_artist_rule(rule)
-      {:ok, 10}
-
-      iex> apply_artist_rule(rule)
-      {:error, :invalid_rule_type}
-
-  """
+  @spec apply_artist_rule(ScrobbleRule.t()) :: {:ok, non_neg_integer()} | {:error, term()}
   def apply_artist_rule(%ScrobbleRule{type: :artist} = rule) do
     update_query =
       from(t in Track,
@@ -303,18 +202,8 @@ defmodule MusicLibrary.ScrobbleRules do
     end
   end
 
-  @doc """
-  Applies an artist rule to a specific set of scrobbled tracks.
-
-  ## Examples
-
-      iex> apply_artist_rule(rule, tracks)
-      {:ok, 7}
-
-      iex> apply_artist_rule(rule, tracks)
-      {:error, :invalid_rule_type}
-
-  """
+  @spec apply_artist_rule(ScrobbleRule.t(), [LastFm.Track.t()]) ::
+          {:ok, non_neg_integer()} | {:error, term()}
   def apply_artist_rule(%ScrobbleRule{type: :artist} = rule, tracks) do
     track_scrobbled_at_uts = Enum.map(tracks, & &1.scrobbled_at_uts)
 
@@ -341,18 +230,7 @@ defmodule MusicLibrary.ScrobbleRules do
     end
   end
 
-  @doc """
-  Applies a single rule based on its type.
-
-  ## Examples
-
-      iex> apply_rule(rule)
-      {:ok, 5}
-
-      iex> apply_rule(rule)
-      {:error, "Invalid rule type"}
-
-  """
+  @spec apply_rule(ScrobbleRule.t()) :: {:ok, non_neg_integer()} | {:error, term()}
   def apply_rule(%ScrobbleRule{type: :album} = rule) do
     apply_album_rule(rule)
   end
@@ -361,18 +239,8 @@ defmodule MusicLibrary.ScrobbleRules do
     apply_artist_rule(rule)
   end
 
-  @doc """
-  Applies a single rule to a specific set of tracks based on its type.
-
-  ## Examples
-
-      iex> apply_rule(rule, tracks)
-      {:ok, 3}
-
-      iex> apply_rule(rule, tracks)
-      {:error, "Invalid rule type"}
-
-  """
+  @spec apply_rule(ScrobbleRule.t(), [LastFm.Track.t()]) ::
+          {:ok, non_neg_integer()} | {:error, term()}
   def apply_rule(%ScrobbleRule{type: :album} = rule, tracks) do
     apply_album_rule(rule, tracks)
   end
@@ -386,13 +254,9 @@ defmodule MusicLibrary.ScrobbleRules do
 
   Uses a CASE statement to update the musicbrainz_id for all matching albums
   in one database operation, which is more efficient than applying rules individually.
-
-  ## Examples
-
-      iex> apply_all_album_rules([rule1, rule2])
-      {:ok, 15}
-
   """
+  @spec apply_all_album_rules([ScrobbleRule.t()]) ::
+          {:ok, non_neg_integer()} | {:error, term()}
   def apply_all_album_rules([]), do: {:ok, 0}
 
   def apply_all_album_rules(rules) when is_list(rules) do
@@ -404,13 +268,9 @@ defmodule MusicLibrary.ScrobbleRules do
 
   Uses a CASE statement to update the musicbrainz_id for all matching albums
   in one database operation, filtering by the provided tracks.
-
-  ## Examples
-
-      iex> apply_all_album_rules([rule1, rule2], tracks)
-      {:ok, 3}
-
   """
+  @spec apply_all_album_rules([ScrobbleRule.t()], [LastFm.Track.t()]) ::
+          {:ok, non_neg_integer()} | {:error, term()}
   def apply_all_album_rules([], _tracks), do: {:ok, 0}
   def apply_all_album_rules(_rules, []), do: {:ok, 0}
 
@@ -423,13 +283,9 @@ defmodule MusicLibrary.ScrobbleRules do
 
   Uses a CASE statement to update the musicbrainz_id for all matching artists
   in one database operation, which is more efficient than applying rules individually.
-
-  ## Examples
-
-      iex> apply_all_artist_rules([rule1, rule2])
-      {:ok, 25}
-
   """
+  @spec apply_all_artist_rules([ScrobbleRule.t()]) ::
+          {:ok, non_neg_integer()} | {:error, term()}
   def apply_all_artist_rules([]), do: {:ok, 0}
 
   def apply_all_artist_rules(rules) when is_list(rules) do
@@ -441,13 +297,9 @@ defmodule MusicLibrary.ScrobbleRules do
 
   Uses a CASE statement to update the musicbrainz_id for all matching artists
   in one database operation, filtering by the provided tracks.
-
-  ## Examples
-
-      iex> apply_all_artist_rules([rule1, rule2], tracks)
-      {:ok, 7}
-
   """
+  @spec apply_all_artist_rules([ScrobbleRule.t()], [LastFm.Track.t()]) ::
+          {:ok, non_neg_integer()} | {:error, term()}
   def apply_all_artist_rules([], _tracks), do: {:ok, 0}
   def apply_all_artist_rules(_rules, []), do: {:ok, 0}
 
@@ -461,13 +313,11 @@ defmodule MusicLibrary.ScrobbleRules do
   This optimized version groups rules by type and applies all rules of each type
   in a single database query, which is much more efficient than applying each rule
   individually.
-
-  ## Examples
-
-      iex> apply_all_rules()
-      {:ok, [{:album, 5}, {:artist, 10}]}
-
   """
+  @spec apply_all_rules() :: [
+          {:ok, {atom(), String.t(), non_neg_integer()}}
+          | {:error, {atom(), String.t(), term()}}
+        ]
   def apply_all_rules do
     :telemetry.span([:music_library, :scrobble_rules, :apply_all_rules], %{}, fn ->
       enabled_rules = list_enabled_rules()
@@ -519,13 +369,11 @@ defmodule MusicLibrary.ScrobbleRules do
 
   This optimized version groups rules by type and applies all rules of each type
   in a single database query, filtering by the provided tracks.
-
-  ## Examples
-
-      iex> apply_all_rules(tracks)
-      [{:ok, {:album, "Some Album", 5}}, {:error, {:artist, "Some Artist", "reason"}}]
-
   """
+  @spec apply_all_rules([LastFm.Track.t()]) :: [
+          {:ok, {atom(), String.t(), non_neg_integer()}}
+          | {:error, {atom(), String.t(), term()}}
+        ]
   def apply_all_rules([]) do
     list_enabled_rules()
     |> Enum.map(fn rule ->
@@ -575,15 +423,7 @@ defmodule MusicLibrary.ScrobbleRules do
     end)
   end
 
-  @doc """
-  Counts how many tracks would be affected by an album rule.
-
-  ## Examples
-
-      iex> count_album_matches(rule)
-      5
-
-  """
+  @spec count_album_matches(ScrobbleRule.t()) :: non_neg_integer()
   def count_album_matches(%ScrobbleRule{type: :album} = rule) do
     query =
       from(t in Track,
@@ -594,15 +434,7 @@ defmodule MusicLibrary.ScrobbleRules do
     Repo.one(query) || 0
   end
 
-  @doc """
-  Counts how many tracks would be affected by an artist rule.
-
-  ## Examples
-
-      iex> count_artist_matches(rule)
-      10
-
-  """
+  @spec count_artist_matches(ScrobbleRule.t()) :: non_neg_integer()
   def count_artist_matches(%ScrobbleRule{type: :artist} = rule) do
     query =
       from(t in Track,
@@ -613,15 +445,7 @@ defmodule MusicLibrary.ScrobbleRules do
     Repo.one(query) || 0
   end
 
-  @doc """
-  Counts how many tracks would be affected by a rule.
-
-  ## Examples
-
-      iex> count_rule_matches(rule)
-      5
-
-  """
+  @spec count_rule_matches(ScrobbleRule.t()) :: non_neg_integer()
   def count_rule_matches(%ScrobbleRule{type: :album} = rule) do
     count_album_matches(rule)
   end
@@ -635,13 +459,11 @@ defmodule MusicLibrary.ScrobbleRules do
 
   Takes a list of results from rule application and logs summary statistics
   and any errors that occurred.
-
-  ## Examples
-
-      iex> log_apply_results([{:ok, {:album, "Album", 5}}, {:error, {:artist, "Artist", "reason"}}])
-      :ok
-
   """
+  @spec log_apply_results([
+          {:ok, {atom(), String.t(), non_neg_integer()}}
+          | {:error, {atom(), String.t(), term()}}
+        ]) :: :ok
   def log_apply_results(results) do
     {applied, errors} =
       Enum.split_with(results, fn
diff --git a/lib/music_library/scrobble_rules/scrobble_rule.ex b/lib/music_library/scrobble_rules/scrobble_rule.ex
index 2530ca56..be2b9edb 100644
--- a/lib/music_library/scrobble_rules/scrobble_rule.ex
+++ b/lib/music_library/scrobble_rules/scrobble_rule.ex
@@ -25,6 +25,7 @@ defmodule MusicLibrary.ScrobbleRules.ScrobbleRule do
   end
 
   @doc false
+  @spec changeset(t() | Ecto.Changeset.t(), map()) :: Ecto.Changeset.t()
   def changeset(scrobble_rule, attrs) do
     scrobble_rule
     |> cast(attrs, [:type, :match_value, :target_musicbrainz_id, :enabled, :description])
diff --git a/lib/music_library/search.ex b/lib/music_library/search.ex
index 6af2601e..f153ab1e 100644
--- a/lib/music_library/search.ex
+++ b/lib/music_library/search.ex
@@ -16,6 +16,8 @@ defmodule MusicLibrary.Search do
 
   @pagination Application.compile_env!(:music_library, :pagination)
 
+  @type search_opts :: [limit: non_neg_integer()]
+
   @doc """
   Performs a universal search across all entity types.
 
@@ -23,10 +25,8 @@ defmodule MusicLibrary.Search do
   - :collection - Records in the collection
   - :wishlist - Records in the wishlist
   - :artists - Artists
-
-  Options:
-  - :limit - Limit per category (default: 5)
   """
+  @spec universal_search(String.t(), search_opts()) :: map()
   def universal_search(query, opts \\ []) do
     limit = Keyword.get(opts, :limit, @pagination[:search_preview_limit])
 
@@ -41,6 +41,7 @@ defmodule MusicLibrary.Search do
   @doc """
   Searches records in the collection (purchased records).
   """
+  @spec search_collection(String.t(), non_neg_integer()) :: [map()]
   def search_collection(query, limit \\ @pagination[:search_preview_limit]) do
     Collection.search_records(query, limit: limit)
   end
@@ -48,6 +49,7 @@ defmodule MusicLibrary.Search do
   @doc """
   Searches records in the wishlist (unpurchased records).
   """
+  @spec search_wishlist(String.t(), non_neg_integer()) :: [map()]
   def search_wishlist(query, limit \\ @pagination[:search_preview_limit]) do
     Wishlist.search_records(query, limit: limit)
   end
@@ -58,6 +60,7 @@ defmodule MusicLibrary.Search do
   Searches across artist names in the artist_records table,
   returning distinct artists that match the query.
   """
+  @spec search_artists(String.t(), non_neg_integer()) :: [map()]
   def search_artists(query, limit \\ @pagination[:search_preview_limit]) do
     case String.trim(query) do
       "" ->
@@ -86,9 +89,10 @@ defmodule MusicLibrary.Search do
 
   Returns a map with counts for each category:
   - :collection_count
-  - :wishlist_count  
+  - :wishlist_count
   - :artists_count
   """
+  @spec search_counts(String.t()) :: map()
   def search_counts(query) do
     %{
       collection_count: Collection.search_records_count(query),
@@ -101,6 +105,7 @@ defmodule MusicLibrary.Search do
   @doc """
   Searches record sets by name, description, and contained records.
   """
+  @spec search_record_sets(String.t(), non_neg_integer()) :: [map()]
   def search_record_sets(query, limit \\ @pagination[:search_preview_limit]) do
     RecordSets.search_record_sets(query, limit: limit)
   end
@@ -108,6 +113,7 @@ defmodule MusicLibrary.Search do
   @doc """
   Gets the count of artists matching the search query.
   """
+  @spec search_artists_count(String.t()) :: non_neg_integer()
   def search_artists_count(query) do
     case String.trim(query) do
       "" ->
diff --git a/lib/music_library/secrets.ex b/lib/music_library/secrets.ex
index 59747296..da1e0279 100644
--- a/lib/music_library/secrets.ex
+++ b/lib/music_library/secrets.ex
@@ -2,16 +2,19 @@ defmodule MusicLibrary.Secrets do
   alias MusicLibrary.Repo
   alias MusicLibrary.Secrets.Secret
 
+  @spec store(String.t(), String.t()) :: {:ok, Secret.t()} | {:error, Ecto.Changeset.t()}
   def store(name, value) do
     %Secret{}
     |> Secret.changeset(%{name: name, value: value})
     |> Repo.insert(on_conflict: :replace_all)
   end
 
+  @spec get!(String.t()) :: Secret.t()
   def get!(name) do
     Repo.get!(Secret, name)
   end
 
+  @spec get(String.t()) :: Secret.t() | nil
   def get(name) do
     Repo.get(Secret, name)
   end
diff --git a/lib/music_library/secrets/secret.ex b/lib/music_library/secrets/secret.ex
index 2b6ac921..c5944204 100644
--- a/lib/music_library/secrets/secret.ex
+++ b/lib/music_library/secrets/secret.ex
@@ -10,6 +10,9 @@ defmodule MusicLibrary.Secrets.Secret do
     timestamps(type: :utc_datetime)
   end
 
+  @type t :: %__MODULE__{}
+
+  @spec changeset(t() | Ecto.Changeset.t(), map()) :: Ecto.Changeset.t()
   def changeset(secret, attrs) do
     secret
     |> cast(attrs, [:name, :value])
diff --git a/lib/music_library/types.ex b/lib/music_library/types.ex
new file mode 100644
index 00000000..f4d1b92f
--- /dev/null
+++ b/lib/music_library/types.ex
@@ -0,0 +1,9 @@
+defmodule MusicLibrary.Types do
+  @moduledoc false
+
+  @type pagination_opts :: [
+          limit: non_neg_integer(),
+          offset: non_neg_integer(),
+          order: atom()
+        ]
+end
diff --git a/lib/music_library/wishlist.ex b/lib/music_library/wishlist.ex
index 229ccf86..53693145 100644
--- a/lib/music_library/wishlist.ex
+++ b/lib/music_library/wishlist.ex
@@ -7,6 +7,7 @@ defmodule MusicLibrary.Wishlist do
 
   @pagination Application.compile_env!(:music_library, :pagination)
 
+  @spec search_records(String.t(), MusicLibrary.Types.pagination_opts()) :: [SearchIndex.t()]
   def search_records(query, opts \\ []) do
     limit = Keyword.get(opts, :limit, @pagination[:default_page_size])
     offset = Keyword.get(opts, :offset, 0)
@@ -15,14 +16,17 @@ defmodule MusicLibrary.Wishlist do
     Records.search_records(base_search(), query, limit: limit, offset: offset, order: order)
   end
 
+  @spec search_records_count(String.t()) :: non_neg_integer()
   def search_records_count(query) do
     Records.search_records_count(base_search(), query)
   end
 
+  @spec count() :: non_neg_integer()
   def count do
     Repo.aggregate(base_search(), :count)
   end
 
+  @spec wishlisted_releases_query() :: Ecto.Query.t()
   def wishlisted_releases_query do
     from rr in RecordRelease,
       where: is_nil(rr.purchased_at),
diff --git a/lib/music_library_web/auth.ex b/lib/music_library_web/auth.ex
index f862d904..14ce9dd7 100644
--- a/lib/music_library_web/auth.ex
+++ b/lib/music_library_web/auth.ex
@@ -5,10 +5,12 @@ defmodule MusicLibraryWeb.Auth do
   import Phoenix.Controller, only: [redirect: 2]
   import Plug.Conn
 
+  @spec correct_login_password?(String.t()) :: boolean()
   def correct_login_password?(password) do
     Plug.Crypto.secure_compare(login_password(), password)
   end
 
+  @spec require_api_token(Plug.Conn.t(), keyword()) :: Plug.Conn.t()
   def require_api_token(conn, _opts) do
     with ["Bearer " <> token] <- get_req_header(conn, "authorization"),
          true <- Plug.Crypto.secure_compare(api_token(), token) do
@@ -31,6 +33,7 @@ defmodule MusicLibraryWeb.Auth do
     |> Keyword.fetch!(:api_token)
   end
 
+  @spec require_logged_in(Plug.Conn.t(), keyword()) :: Plug.Conn.t()
   def require_logged_in(conn, _opts) do
     if get_session(conn, :logged_in) do
       conn
diff --git a/lib/music_library_web/components/pagination.ex b/lib/music_library_web/components/pagination.ex
index 9b22fd9f..d68c01c3 100644
--- a/lib/music_library_web/components/pagination.ex
+++ b/lib/music_library_web/components/pagination.ex
@@ -162,6 +162,7 @@ defmodule MusicLibraryWeb.Components.Pagination do
     """
   end
 
+  @spec page_to_offset(pos_integer(), pos_integer()) :: non_neg_integer()
   def page_to_offset(page, per_page) do
     (page - 1) * per_page
   end
diff --git a/lib/music_library_web/duration.ex b/lib/music_library_web/duration.ex
index e609b0d4..fcd8d6d6 100644
--- a/lib/music_library_web/duration.ex
+++ b/lib/music_library_web/duration.ex
@@ -21,6 +21,7 @@ defmodule MusicLibraryWeb.Duration do
       "0:00"
 
   """
+  @spec format_duration(non_neg_integer()) :: String.t()
   def format_duration(milliseconds) do
     milliseconds
     |> System.convert_time_unit(:millisecond, :second)
diff --git a/lib/music_library_web/error_messages.ex b/lib/music_library_web/error_messages.ex
index 943e0f16..5490b4cb 100644
--- a/lib/music_library_web/error_messages.ex
+++ b/lib/music_library_web/error_messages.ex
@@ -9,6 +9,8 @@ defmodule MusicLibraryWeb.ErrorMessages do
 
   use Gettext, backend: MusicLibraryWeb.Gettext
 
+  @spec friendly_message(term()) :: String.t()
+
   # App error atoms
   def friendly_message(:cover_not_available), do: gettext("cover art is not available")
   def friendly_message(:no_duration), do: gettext("release has no track duration information")
diff --git a/lib/music_library_web/live_helpers/params.ex b/lib/music_library_web/live_helpers/params.ex
index f19085ef..4bfaf928 100644
--- a/lib/music_library_web/live_helpers/params.ex
+++ b/lib/music_library_web/live_helpers/params.ex
@@ -1,6 +1,7 @@
 defmodule MusicLibraryWeb.LiveHelpers.Params do
   @pagination Application.compile_env!(:music_library, :pagination)
 
+  @spec parse_page(String.t() | nil | term()) :: pos_integer()
   def parse_page(nil), do: 1
 
   def parse_page(page) when is_binary(page) do
@@ -12,6 +13,8 @@ defmodule MusicLibraryWeb.LiveHelpers.Params do
 
   def parse_page(_), do: 1
 
+  @spec parse_page_size(String.t() | nil | term(), [pos_integer()] | nil, pos_integer()) ::
+          pos_integer()
   def parse_page_size(nil, _allowed, default), do: default
 
   def parse_page_size(page_size, allowed, default) when is_binary(page_size) do
@@ -26,6 +29,7 @@ defmodule MusicLibraryWeb.LiveHelpers.Params do
 
   def parse_page_size(_, _allowed, default), do: default
 
+  @spec merge_pagination(map(), map(), non_neg_integer(), keyword()) :: map()
   def merge_pagination(params, url_params, total_entries, opts \\ []) do
     allowed = Keyword.get(opts, :allowed_page_sizes)
     default_page_size = params[:page_size] || @pagination[:default_page_size]
@@ -39,14 +43,18 @@ defmodule MusicLibraryWeb.LiveHelpers.Params do
     |> Map.put(:total_entries, total_entries)
   end
 
+  @spec merge_query(map(), String.t() | nil) :: map()
   def merge_query(params, query) do
     Map.put(params, :query, query)
   end
 
+  @spec merge_order(map(), atom()) :: map()
   def merge_order(params, order) do
     Map.put(params, :order, order)
   end
 
+  @spec apply_fallback_index(Phoenix.LiveView.Socket.t(), map(), atom(), function()) ::
+          Phoenix.LiveView.Socket.t()
   def apply_fallback_index(socket, params, stream_key, apply_action_fn) do
     if get_in(socket.assigns, [:streams, stream_key]) == nil do
       apply_action_fn.(socket, :index, params)
diff --git a/lib/music_library_web/markdown.ex b/lib/music_library_web/markdown.ex
index 4c280662..28f23535 100644
--- a/lib/music_library_web/markdown.ex
+++ b/lib/music_library_web/markdown.ex
@@ -12,6 +12,7 @@ defmodule MusicLibraryWeb.Markdown do
 
   Double square brackets are converted to search links before the markdown is processed.
   """
+  @spec to_html(String.t() | nil) :: String.t()
   def to_html(markdown_text) when is_binary(markdown_text) do
     markdown_text
     |> process_double_bracket_links()
@@ -41,6 +42,7 @@ defmodule MusicLibraryWeb.Markdown do
       iex> MusicLibraryWeb.Markdown.process_double_bracket_links(~s|[[genre:"psychedelic rock"]]|)
       ~s|[psychedelic rock](/collection?query=genre%3A%22psychedelic+rock%22)|
   """
+  @spec process_double_bracket_links(String.t()) :: String.t()
   def process_double_bracket_links(text) do
     ~r/\[\[([^\]]+)\]\]/
     |> Regex.replace(text, fn _match, content ->
diff --git a/lib/open_ai.ex b/lib/open_ai.ex
index 0be81511..76bd26a3 100644
--- a/lib/open_ai.ex
+++ b/lib/open_ai.ex
@@ -1,10 +1,19 @@
 defmodule OpenAI do
   alias OpenAI.API
 
+  @type chat_stream_opts :: [
+          model: String.t(),
+          temperature: float(),
+          instructions: String.t(),
+          on_chunk: (String.t() -> any())
+        ]
+
+  @spec gpt(OpenAI.Completion.t()) :: {:ok, map()} | {:error, term()}
   def gpt(completion) do
     API.gpt(completion, config())
   end
 
+  @spec chat_stream([map()], chat_stream_opts()) :: :ok | {:error, String.t()}
   def chat_stream(messages, opts \\ []) when is_list(messages) do
     model = Keyword.get(opts, :model, "gpt-4.1")
     temperature = Keyword.get(opts, :temperature, 0.7)
@@ -17,6 +26,7 @@ defmodule OpenAI do
     end
   end
 
+  @spec embeddings(String.t()) :: {:ok, [float()]} | {:error, term()}
   def embeddings(text) do
     API.get_embeddings(text, config())
   end
diff --git a/lib/open_ai/api.ex b/lib/open_ai/api.ex
index a079e04a..bd807bff 100644
--- a/lib/open_ai/api.ex
+++ b/lib/open_ai/api.ex
@@ -1,6 +1,7 @@
 defmodule OpenAI.API do
   require Logger
 
+  @spec gpt(OpenAI.Completion.t(), OpenAI.Config.t()) :: {:ok, map()} | {:error, term()}
   def gpt(completion, config) do
     resp =
       config
@@ -26,6 +27,9 @@ defmodule OpenAI.API do
     end
   end
 
+  @spec chat_stream([map()], String.t(), String.t(), float(), OpenAI.Config.t(), (String.t() ->
+                                                                                    any())) ::
+          :ok | {:error, String.t()}
   def chat_stream(messages, instructions, model, temperature, config, cb) do
     case config
          |> new_request()
@@ -60,6 +64,7 @@ defmodule OpenAI.API do
     end
   end
 
+  @spec get_embeddings(String.t(), OpenAI.Config.t()) :: {:ok, [float()]} | {:error, term()}
   def get_embeddings(text, config) do
     resp =
       config
diff --git a/lib/open_ai/completion.ex b/lib/open_ai/completion.ex
index 842e7795..214a157e 100644
--- a/lib/open_ai/completion.ex
+++ b/lib/open_ai/completion.ex
@@ -4,4 +4,11 @@ defmodule OpenAI.Completion do
             temperature: 0.2,
             role: "user",
             model: "gpt-4o-mini"
+
+  @type t :: %__MODULE__{
+          content: String.t(),
+          temperature: float(),
+          role: String.t(),
+          model: String.t()
+        }
 end
diff --git a/lib/req/rate_limiter.ex b/lib/req/rate_limiter.ex
index ff336e93..c0e1795e 100644
--- a/lib/req/rate_limiter.ex
+++ b/lib/req/rate_limiter.ex
@@ -20,6 +20,9 @@ defmodule Req.RateLimiter do
   Creates the ETS table used to track request timestamps.
   Call once at application startup.
   """
+  @type attach_opts :: [name: atom(), cooldown: non_neg_integer()]
+
+  @spec new() :: :ets.table()
   def new do
     :ets.new(@table, [:set, :public, :named_table])
   end
@@ -33,6 +36,7 @@ defmodule Req.RateLimiter do
     * `:cooldown` - minimum milliseconds between requests
 
   """
+  @spec attach(Req.Request.t(), attach_opts()) :: Req.Request.t()
   def attach(request, opts) do
     name = Keyword.fetch!(opts, :name)
     cooldown = Keyword.fetch!(opts, :cooldown)
diff --git a/lib/sqlite_vec/ecto/float32.ex b/lib/sqlite_vec/ecto/float32.ex
index 83462c63..c519fa90 100644
--- a/lib/sqlite_vec/ecto/float32.ex
+++ b/lib/sqlite_vec/ecto/float32.ex
@@ -4,16 +4,24 @@ defmodule SqliteVec.Ecto.Float32 do
   """
   use Ecto.Type
 
+  @impl true
+  @spec type() :: :binary
   def type, do: :binary
 
+  @impl true
+  @spec cast(any()) :: {:ok, SqliteVec.Float32.t()}
   def cast(value) do
     {:ok, SqliteVec.Float32.new(value)}
   end
 
+  @impl true
+  @spec load(binary()) :: {:ok, SqliteVec.Float32.t()}
   def load(data) do
     {:ok, SqliteVec.Float32.from_binary(data)}
   end
 
+  @impl true
+  @spec dump(SqliteVec.Float32.t()) :: {:ok, binary()} | :error
   def dump(%SqliteVec.Float32{} = vector) do
     {:ok, SqliteVec.Float32.to_binary(vector)}
   end
diff --git a/lib/sqlite_vec/ecto/query.ex b/lib/sqlite_vec/ecto/query.ex
index 503490e9..60f603d3 100644
--- a/lib/sqlite_vec/ecto/query.ex
+++ b/lib/sqlite_vec/ecto/query.ex
@@ -75,6 +75,9 @@ defmodule SqliteVec.Ecto.Query do
     end
   end
 
+  @doc """
+  Matches a vector against a virtual table using the `match` operator.
+  """
   defmacro vec_match(a, b) do
     quote do
       fragment("? match ?", unquote(a), unquote(b))
diff --git a/lib/sqlite_vec/float32.ex b/lib/sqlite_vec/float32.ex
index ac0668bb..6ef8a9ae 100644
--- a/lib/sqlite_vec/float32.ex
+++ b/lib/sqlite_vec/float32.ex
@@ -41,6 +41,7 @@ defmodule SqliteVec.Float32 do
       iex> SqliteVec.Float32.new(Nx.tensor([1, 2], type: :f32))
       %SqliteVec.Float32{data: <<1.0::float-32-native, 2.0::float-32-native>>}
   """
+  @spec new(t() | [number()]) :: t()
   def new(vector_or_list_or_tensor)
 
   def new(%SqliteVec.Float32{} = vector) do
@@ -74,6 +75,7 @@ defmodule SqliteVec.Float32 do
   @doc """
   Creates a new vector from its binary representation
   """
+  @spec from_binary(binary()) :: t()
   def from_binary(binary) when is_binary(binary) do
     %SqliteVec.Float32{data: binary}
   end
@@ -81,6 +83,7 @@ defmodule SqliteVec.Float32 do
   @doc """
   Converts the vector to its binary representation
   """
+  @spec to_binary(t()) :: binary()
   def to_binary(vector) when is_struct(vector, SqliteVec.Float32) do
     vector.data
   end
@@ -88,6 +91,7 @@ defmodule SqliteVec.Float32 do
   @doc """
   Converts the vector to a list
   """
+  @spec to_list(t()) :: [float()]
   def to_list(vector) when is_struct(vector, SqliteVec.Float32) do
     <<bin::binary>> = vector.data
 
diff --git a/lib/wikipedia.ex b/lib/wikipedia.ex
index 91cd9885..776894d3 100644
--- a/lib/wikipedia.ex
+++ b/lib/wikipedia.ex
@@ -1,6 +1,7 @@
 defmodule Wikipedia do
   alias Wikipedia.API
 
+  @spec get_artist_summary(String.t()) :: {:ok, map()} | {:error, :no_english_wikipedia | term()}
   def get_artist_summary(wikidata_id) do
     config = wikipedia_config()
 
diff --git a/lib/wikipedia/api.ex b/lib/wikipedia/api.ex
index 2ca8d0b1..627301f9 100644
--- a/lib/wikipedia/api.ex
+++ b/lib/wikipedia/api.ex
@@ -5,6 +5,8 @@ defmodule Wikipedia.API do
 
   require Logger
 
+  @spec get_wikipedia_title(String.t(), Wikipedia.Config.t()) ::
+          {:ok, String.t() | nil} | {:error, term()}
   def get_wikipedia_title(wikidata_id, config) do
     request =
       Req.new(
@@ -41,6 +43,7 @@ defmodule Wikipedia.API do
     end
   end
 
+  @spec get_article_summary(String.t(), Wikipedia.Config.t()) :: {:ok, map()} | {:error, term()}
   def get_article_summary(title, config) do
     request =
       Req.new(
@@ -65,6 +68,8 @@ defmodule Wikipedia.API do
     end
   end
 
+  @spec get_article_extract(String.t(), Wikipedia.Config.t()) ::
+          {:ok, String.t() | nil} | {:error, term()}
   def get_article_extract(title, config) do
     request =
       Req.new(