diff --git a/lib/mix/tasks/reindex_all.ex b/lib/mix/tasks/reindex_all.ex
index 274c658d..2af00554 100644
--- a/lib/mix/tasks/reindex_all.ex
+++ b/lib/mix/tasks/reindex_all.ex
@@ -18,9 +18,10 @@ defmodule Mix.Tasks.ReindexAll do
   import Ecto.Query
 
   @shortdoc "Destroys and recreates all Elasticsearch indices."
-  def run(_) do
-    if Mix.env() == :prod and not Enum.member?(System.argv(), "--i-know-what-im-doing") do
-      raise "do not run this task in production"
+  @impl Mix.Task
+  def run(args) do
+    if Mix.env() == :prod and not Enum.member?(args, "--i-know-what-im-doing") do
+      raise "do not run this task unless you know what you're doing"
     end
 
     {:ok, _apps} = Application.ensure_all_started(:philomena)
diff --git a/lib/philomena/images/tag_validator.ex b/lib/philomena/images/tag_validator.ex
index 288b3ae4..4328dd1c 100644
--- a/lib/philomena/images/tag_validator.ex
+++ b/lib/philomena/images/tag_validator.ex
@@ -2,12 +2,6 @@ defmodule Philomena.Images.TagValidator do
   alias Philomena.Servers.Config
   import Ecto.Changeset
 
-  @safe_rating MapSet.new(["safe"])
-  @sexual_ratings MapSet.new(["suggestive", "questionable", "explicit"])
-  @horror_ratings MapSet.new(["semi-grimdark", "grimdark"])
-  @gross_rating MapSet.new(["grotesque"])
-  @empty MapSet.new()
-
   def validate_tags(changeset) do
     tags = changeset |> get_field(:tags)
 
@@ -27,11 +21,11 @@ defmodule Philomena.Images.TagValidator do
     |> validate_horror_exclusion(rating_set)
   end
 
-  defp ratings(%MapSet{} = tag_set) do
-    safe = MapSet.intersection(tag_set, @safe_rating)
-    sexual = MapSet.intersection(tag_set, @sexual_ratings)
-    horror = MapSet.intersection(tag_set, @horror_ratings)
-    gross = MapSet.intersection(tag_set, @gross_rating)
+  defp ratings(tag_set) do
+    safe = MapSet.intersection(tag_set, safe_rating())
+    sexual = MapSet.intersection(tag_set, sexual_ratings())
+    horror = MapSet.intersection(tag_set, horror_ratings())
+    gross = MapSet.intersection(tag_set, gross_rating())
 
     %{
       safe: safe,
@@ -44,8 +38,7 @@ defmodule Philomena.Images.TagValidator do
   defp validate_number_of_tags(changeset, tag_set, num) do
     cond do
       MapSet.size(tag_set) < num ->
-        changeset
-        |> add_error(:tag_input, "must contain at least #{num} tags")
+        add_error(changeset, :tag_input, "must contain at least #{num} tags")
 
       true ->
         changeset
@@ -69,27 +62,30 @@ defmodule Philomena.Images.TagValidator do
     end
   end
 
-  defp validate_has_rating(changeset, %{safe: s, sexual: x, horror: h, gross: g})
-       when s == @empty and x == @empty and h == @empty and g == @empty do
-    changeset
-    |> add_error(:tag_input, "must contain at least one rating tag")
+  defp validate_has_rating(changeset, %{safe: s, sexual: x, horror: h, gross: g}) do
+    cond do
+      MapSet.size(s) > 0 or MapSet.size(x) > 0 or MapSet.size(h) > 0 or MapSet.size(g) > 0 ->
+        changeset
+
+      true ->
+        add_error(changeset, :tag_input, "must contain at least one rating tag")
+    end
   end
 
-  defp validate_has_rating(changeset, _ratings), do: changeset
+  defp validate_safe(changeset, %{safe: s, sexual: x, horror: h, gross: g}) do
+    cond do
+      MapSet.size(s) > 1 and (MapSet.size(x) > 0 or MapSet.size(h) > 0 or MapSet.size(g) > 0) ->
+        add_error(changeset, :tag_input, "may not contain any other rating if safe")
 
-  defp validate_safe(changeset, %{safe: s, sexual: x, horror: h, gross: g})
-       when s != @empty and (x != @empty or h != @empty or g != @empty) do
-    changeset
-    |> add_error(:tag_input, "may not contain any other rating if safe")
+      true ->
+        changeset
+    end
   end
 
-  defp validate_safe(changeset, _ratings), do: changeset
-
   defp validate_sexual_exclusion(changeset, %{sexual: x}) do
     cond do
       MapSet.size(x) > 1 ->
-        changeset
-        |> add_error(:tag_input, "may contain at most one sexual rating")
+        add_error(changeset, :tag_input, "may contain at most one sexual rating")
 
       true ->
         changeset
@@ -99,8 +95,7 @@ defmodule Philomena.Images.TagValidator do
   defp validate_horror_exclusion(changeset, %{horror: h}) do
     cond do
       MapSet.size(h) > 1 ->
-        changeset
-        |> add_error(:tag_input, "may contain at most one grim rating")
+        add_error(changeset, :tag_input, "may contain at most one grim rating")
 
       true ->
         changeset
@@ -112,4 +107,9 @@ defmodule Philomena.Images.TagValidator do
     |> Enum.map(& &1.name)
     |> MapSet.new()
   end
+
+  defp safe_rating, do: MapSet.new(["safe"])
+  defp sexual_ratings, do: MapSet.new(["suggestive", "questionable", "explicit"])
+  defp horror_ratings, do: MapSet.new(["semi-grimdark", "grimdark"])
+  defp gross_rating, do: MapSet.new(["grotesque"])
 end
diff --git a/lib/philomena/search/date_parser.ex b/lib/philomena/search/date_parser.ex
index 1434b970..4b3bf72a 100644
--- a/lib/philomena/search/date_parser.ex
+++ b/lib/philomena/search/date_parser.ex
@@ -1,5 +1,6 @@
 defmodule Philomena.Search.DateParser do
   import NimbleParsec
+  @dialyzer [:no_match, :no_unused]
 
   defp build_datetime(naive, tz_off, tz_hour, tz_minute) do
     tz_hour =
diff --git a/lib/philomena/search/literal_parser.ex b/lib/philomena/search/literal_parser.ex
index 905e7f72..ac291612 100644
--- a/lib/philomena/search/literal_parser.ex
+++ b/lib/philomena/search/literal_parser.ex
@@ -1,5 +1,6 @@
 defmodule Philomena.Search.LiteralParser do
   import NimbleParsec
+  @dialyzer [:no_match, :no_unused]
 
   defp to_number(input), do: Philomena.Search.Helpers.to_number(input)
 
diff --git a/lib/philomena/tags.ex b/lib/philomena/tags.ex
index e47046a1..878566d1 100644
--- a/lib/philomena/tags.ex
+++ b/lib/philomena/tags.ex
@@ -19,7 +19,7 @@ defmodule Philomena.Tags do
   alias Philomena.DnpEntries.DnpEntry
   alias Philomena.Channels.Channel
 
-  @spec get_or_create_tags(String.t()) :: List.t()
+  @spec get_or_create_tags(String.t()) :: list()
   def get_or_create_tags(tag_list) do
     tag_names = Tag.parse_tag_list(tag_list)
 
diff --git a/lib/philomena/textile/parser.ex b/lib/philomena/textile/parser.ex
index 3f022c6f..deffd546 100644
--- a/lib/philomena/textile/parser.ex
+++ b/lib/philomena/textile/parser.ex
@@ -394,10 +394,6 @@ defmodule Philomena.Textile.Parser do
                {:text, escape(open)},
                tree2
              ], r3_tokens}
-
-          _ ->
-            {:ok, [{:text, escape(start)}, {:text, escape(flatten(tree))}, {:text, escape(open)}],
-             r_tokens}
         end
 
       _ ->
diff --git a/lib/philomena/users/user.ex b/lib/philomena/users/user.ex
index 1430c0ed..8739fdb3 100644
--- a/lib/philomena/users/user.ex
+++ b/lib/philomena/users/user.ex
@@ -436,16 +436,13 @@ defmodule Philomena.Users.User do
 
     cond do
       totp_valid?(user, token) ->
-        changeset
-        |> change(%{consumed_timestep: String.to_integer(token)})
+        change(changeset, consumed_timestep: String.to_integer(token))
 
       backup_code_valid?(user, token) ->
-        changeset
-        |> change(%{otp_backup_codes: remove_backup_code(user, token)})
+        change(changeset, otp_backup_codes: remove_backup_code(user, token))
 
       true ->
-        changeset
-        |> add_error(:twofactor_token, "Invalid token")
+        add_error(changeset, :twofactor_token, "Invalid token")
     end
   end
 
@@ -500,6 +497,7 @@ defmodule Philomena.Users.User do
     "data:image/png;base64," <> png
   end
 
+  @spec totp_secret(%Philomena.Users.User{}) :: binary()
   def totp_secret(user) do
     Philomena.Users.Encryptor.decrypt_model(
       user.encrypted_otp_secret,
diff --git a/lib/philomena_web/controllers/api/json/image_controller.ex b/lib/philomena_web/controllers/api/json/image_controller.ex
index 4d115c47..6fe81062 100644
--- a/lib/philomena_web/controllers/api/json/image_controller.ex
+++ b/lib/philomena_web/controllers/api/json/image_controller.ex
@@ -7,7 +7,7 @@ defmodule PhilomenaWeb.Api.Json.ImageController do
   alias Philomena.Repo
   import Ecto.Query
 
-  plug :set_scraper_cache
+  plug PhilomenaWeb.ScraperCachePlug
   plug PhilomenaWeb.ApiRequireAuthorizationPlug when action in [:create]
   plug PhilomenaWeb.UserAttributionPlug when action in [:create]
 
@@ -55,13 +55,4 @@ defmodule PhilomenaWeb.Api.Json.ImageController do
         |> render("error.json", changeset: changeset)
     end
   end
-
-  defp set_scraper_cache(conn, _opts) do
-    params =
-      conn.params
-      |> Map.put_new("image", %{})
-      |> Map.put("scraper_cache", conn.params["url"])
-
-    %{conn | params: params}
-  end
 end
diff --git a/lib/philomena_web/controllers/api/json/search/reverse_controller.ex b/lib/philomena_web/controllers/api/json/search/reverse_controller.ex
index d4630c96..e1cf4d7c 100644
--- a/lib/philomena_web/controllers/api/json/search/reverse_controller.ex
+++ b/lib/philomena_web/controllers/api/json/search/reverse_controller.ex
@@ -4,7 +4,7 @@ defmodule PhilomenaWeb.Api.Json.Search.ReverseController do
   alias PhilomenaWeb.ImageReverse
   alias Philomena.Interactions
 
-  plug :set_scraper_cache
+  plug PhilomenaWeb.ScraperCachePlug
   plug PhilomenaWeb.ScraperPlug, params_key: "image", params_name: "image"
 
   def create(conn, %{"image" => image_params}) do
@@ -21,23 +21,4 @@ defmodule PhilomenaWeb.Api.Json.Search.ReverseController do
     |> put_view(PhilomenaWeb.Api.Json.ImageView)
     |> render("index.json", images: images, total: length(images), interactions: interactions)
   end
-
-  defp set_scraper_cache(conn, _opts) do
-    params =
-      conn.params
-      |> Map.put("image", %{})
-      |> Map.put("distance", normalize_dist(conn.params))
-      |> Map.put("scraper_cache", conn.params["url"])
-
-    %{conn | params: params}
-  end
-
-  defp normalize_dist(%{"distance" => distance}) do
-    ("0" <> distance)
-    |> Float.parse()
-    |> elem(0)
-    |> Float.to_string()
-  end
-
-  defp normalize_dist(_dist), do: "0.25"
 end
diff --git a/lib/philomena_web/controllers/search/reverse_controller.ex b/lib/philomena_web/controllers/search/reverse_controller.ex
index 44bf896b..b6c6ba6b 100644
--- a/lib/philomena_web/controllers/search/reverse_controller.ex
+++ b/lib/philomena_web/controllers/search/reverse_controller.ex
@@ -3,7 +3,7 @@ defmodule PhilomenaWeb.Search.ReverseController do
 
   alias PhilomenaWeb.ImageReverse
 
-  plug :set_scraper_cache
+  plug PhilomenaWeb.ScraperCachePlug
   plug PhilomenaWeb.ScraperPlug, params_key: "image", params_name: "image"
 
   def index(conn, params) do
@@ -19,23 +19,4 @@ defmodule PhilomenaWeb.Search.ReverseController do
   def create(conn, _params) do
     render(conn, "index.html", title: "Reverse Search", images: nil)
   end
-
-  defp set_scraper_cache(conn, _opts) do
-    params =
-      conn.params
-      |> Map.put_new("image", %{})
-      |> Map.put_new("scraper_cache", conn.params["url"])
-      |> Map.put("distance", normalize_dist(conn.params))
-
-    %{conn | params: params}
-  end
-
-  defp normalize_dist(%{"distance" => distance}) do
-    ("0" <> distance)
-    |> Float.parse()
-    |> elem(0)
-    |> Float.to_string()
-  end
-
-  defp normalize_dist(_dist), do: "0.25"
 end
diff --git a/lib/philomena_web/image_navigator.ex b/lib/philomena_web/image_navigator.ex
index 4a7dd105..8686f1d8 100644
--- a/lib/philomena_web/image_navigator.ex
+++ b/lib/philomena_web/image_navigator.ex
@@ -92,11 +92,11 @@ defmodule PhilomenaWeb.ImageNavigator do
     field = String.to_existing_atom(sf)
     filter = range_filter(sf, @range_comparison_for_order[order], image[field])
 
-    cond do
-      sf in [:_random, :_score] ->
+    case sf do
+      "_score" ->
         {[sort], []}
 
-      true ->
+      _ ->
         {[sort], [filter]}
     end
   end
diff --git a/lib/philomena_web/plugs/advert_plug.ex b/lib/philomena_web/plugs/advert_plug.ex
index 5dfeb0a3..e2dd23f3 100644
--- a/lib/philomena_web/plugs/advert_plug.ex
+++ b/lib/philomena_web/plugs/advert_plug.ex
@@ -13,6 +13,8 @@ defmodule PhilomenaWeb.AdvertPlug do
     maybe_assign_ad(conn, image, show_ads?)
   end
 
+  defp maybe_assign_ad(conn, image, show_ads?)
+
   defp maybe_assign_ad(conn, nil, true),
     do: Conn.assign(conn, :advert, record_impression(Adverts.random_live()))
 
@@ -22,8 +24,8 @@ defmodule PhilomenaWeb.AdvertPlug do
   defp maybe_assign_ad(conn, _image, _false),
     do: conn
 
-  defp show_ads?(%{hide_advertisements: false}),
-    do: true
+  defp show_ads?(%{hide_advertisements: hide}),
+    do: !hide
 
   defp show_ads?(_user),
     do: true
diff --git a/lib/philomena_web/plugs/scraper_cache_plug.ex b/lib/philomena_web/plugs/scraper_cache_plug.ex
new file mode 100644
index 00000000..02306c73
--- /dev/null
+++ b/lib/philomena_web/plugs/scraper_cache_plug.ex
@@ -0,0 +1,28 @@
+defmodule PhilomenaWeb.ScraperCachePlug do
+  @spec init(any()) :: any()
+  def init(opts) do
+    opts
+  end
+
+  @spec call(Plug.Conn.t(), any()) :: Plug.Conn.t()
+  def call(conn, _opts) do
+    params =
+      conn.params
+      |> Map.put_new("image", %{})
+      |> Map.put_new("scraper_cache", conn.params["url"])
+      |> Map.put("distance", normalize_dist(conn.params))
+
+    %Plug.Conn{conn | params: params}
+  end
+
+  defp normalize_dist(%{"distance" => distance}) do
+    ("0" <> distance)
+    |> Float.parse()
+    |> elem(0)
+    |> Float.to_string()
+  end
+
+  defp normalize_dist(_dist) do
+    "0.25"
+  end
+end
diff --git a/lib/philomena_web/plugs/scraper_plug.ex b/lib/philomena_web/plugs/scraper_plug.ex
index 987d5ccc..41108857 100644
--- a/lib/philomena_web/plugs/scraper_plug.ex
+++ b/lib/philomena_web/plugs/scraper_plug.ex
@@ -1,5 +1,7 @@
 defmodule PhilomenaWeb.ScraperPlug do
-  def init(opts), do: opts
+  def init(opts) do
+    opts
+  end
 
   def call(conn, opts) do
     params_name = Keyword.get(opts, :params_name, "image")
@@ -10,7 +12,8 @@ defmodule PhilomenaWeb.ScraperPlug do
         conn
 
       %{"scraper_cache" => url} when not is_nil(url) ->
-        Philomena.Http.get!(url)
+        url
+        |> Philomena.Http.get!()
         |> maybe_fixup_params(opts, conn)
 
       _ ->
@@ -36,7 +39,7 @@ defmodule PhilomenaWeb.ScraperPlug do
 
     updated_params = Map.put(conn.params, params_name, updated_form)
 
-    %{conn | params: updated_params}
+    %Plug.Conn{conn | params: updated_params}
   end
 
   defp maybe_fixup_params(_response, _opts, conn), do: conn
diff --git a/lib/philomena_web/views/advert_view.ex b/lib/philomena_web/views/advert_view.ex
index c09e8d62..d462d136 100644
--- a/lib/philomena_web/views/advert_view.ex
+++ b/lib/philomena_web/views/advert_view.ex
@@ -5,6 +5,8 @@ defmodule PhilomenaWeb.AdvertView do
     advert_url_root() <> "/" <> image
   end
 
+  def advert_image_url(_), do: nil
+
   defp advert_url_root do
     Application.get_env(:philomena, :advert_url_root)
   end
diff --git a/mix.exs b/mix.exs
index 3249a15c..a22572fb 100644
--- a/mix.exs
+++ b/mix.exs
@@ -10,7 +10,8 @@ defmodule Philomena.MixProject do
       compilers: [:phoenix, :gettext] ++ Mix.compilers(),
       start_permanent: Mix.env() == :prod,
       aliases: aliases(),
-      deps: deps()
+      deps: deps(),
+      dialyzer: [plt_add_apps: [:mix]]
     ]
   end