diff --git a/lib/pleroma/web/admin_api/controllers/tag_controller.ex b/lib/pleroma/web/admin_api/controllers/tag_controller.ex
index 60b5d2ab9..ee48efbd7 100644
--- a/lib/pleroma/web/admin_api/controllers/tag_controller.ex
+++ b/lib/pleroma/web/admin_api/controllers/tag_controller.ex
@@ -10,6 +10,7 @@ defmodule Pleroma.Web.AdminAPI.TagController do
   alias Pleroma.ModerationLog
   alias Pleroma.User
   alias Pleroma.Web.AdminAPI
+  alias Pleroma.Web.ApiSpec
   alias Pleroma.Web.Plugs.OAuthScopesPlug
 
   plug(
@@ -22,15 +23,19 @@ defmodule Pleroma.Web.AdminAPI.TagController do
     %{scopes: ["read:accounts"], admin: true} when action in [:list]
   )
 
+  plug(ApiSpec.CastAndValidate)
+
   action_fallback(AdminAPI.FallbackController)
 
+  defdelegate open_api_operation(action), to: ApiSpec.Admin.TagOperation
+
   def list(%{assigns: %{user: _admin}} = conn, _) do
     tags = Pleroma.Tag.list_tags()
 
     json(conn, tags)
   end
 
-  def tag(%{assigns: %{user: admin}} = conn, %{"nicknames" => nicknames, "tags" => tags}) do
+  def tag(%{assigns: %{user: admin}} = conn, %{nicknames: nicknames, tags: tags}) do
     with {:ok, _} <- User.tag(nicknames, tags) do
       ModerationLog.insert_log(%{
         actor: admin,
@@ -43,7 +48,7 @@ defmodule Pleroma.Web.AdminAPI.TagController do
     end
   end
 
-  def untag(%{assigns: %{user: admin}} = conn, %{"nicknames" => nicknames, "tags" => tags}) do
+  def untag(%{assigns: %{user: admin}} = conn, %{nicknames: nicknames, tags: tags}) do
     with {:ok, _} <- User.untag(nicknames, tags) do
       ModerationLog.insert_log(%{
         actor: admin,
diff --git a/lib/pleroma/web/api_spec/operations/admin/tag_operation.ex b/lib/pleroma/web/api_spec/operations/admin/tag_operation.ex
new file mode 100644
index 000000000..83a6b5c26
--- /dev/null
+++ b/lib/pleroma/web/api_spec/operations/admin/tag_operation.ex
@@ -0,0 +1,83 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2020 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.Web.ApiSpec.Admin.TagOperation do
+  alias OpenApiSpex.Operation
+  alias OpenApiSpex.Schema
+
+  import Pleroma.Web.ApiSpec.Helpers
+
+  def open_api_operation(action) do
+    operation = String.to_existing_atom("#{action}_operation")
+    apply(__MODULE__, operation, [])
+  end
+
+  def list_operation do
+    %Operation{
+      tags: ["Admin", "Tags"],
+      summary: "List available tags.",
+      operationId: "AdminAPI.TagController.list",
+      responses: %{
+        200 =>
+          Operation.response("Array of tags", "application/json", %Schema{
+            type: :array,
+            items: %Schema{type: :string}
+          })
+      },
+      security: [%{"oAuth" => ["read:accounts"]}]
+    }
+  end
+
+  def tag_operation do
+    %Operation{
+      tags: ["Admin", "Tags"],
+      summary: "Adds tags to users.",
+      operationId: "AdminAPI.TagController.tag",
+      parameters: [
+        Operation.parameter(
+          :nicknames,
+          :query,
+          %Schema{type: :array, items: %Schema{type: :string}},
+          "User's nicknames"
+        ),
+        Operation.parameter(
+          :tags,
+          :query,
+          %Schema{type: :array, items: %Schema{type: :string}},
+          "tags"
+        )
+      ],
+      responses: %{
+        200 => empty_object_response()
+      },
+      security: [%{"oAuth" => ["write:accounts"]}]
+    }
+  end
+
+  def untag_operation do
+    %Operation{
+      tags: ["Admin", "Tags"],
+      summary: "Remove tags from users.",
+      operationId: "AdminAPI.TagController.untag",
+      parameters: [
+        Operation.parameter(
+          :nicknames,
+          :query,
+          %Schema{type: :array, items: %Schema{type: :string}},
+          "User's nicknames"
+        ),
+        Operation.parameter(
+          :tags,
+          :query,
+          %Schema{type: :array, items: %Schema{type: :string}},
+          "tags"
+        )
+      ],
+      responses: %{
+        200 => empty_object_response()
+      },
+      security: [%{"oAuth" => ["write:accounts"]}]
+    }
+  end
+end
diff --git a/test/pleroma/web/admin_api/controllers/tag_controller_test.exs b/test/pleroma/web/admin_api/controllers/tag_controller_test.exs
index 1ead1ca76..5d9963dcb 100644
--- a/test/pleroma/web/admin_api/controllers/tag_controller_test.exs
+++ b/test/pleroma/web/admin_api/controllers/tag_controller_test.exs
@@ -40,7 +40,7 @@ defmodule Pleroma.Web.AdminAPI.TagControllerTest do
         conn
         |> put_req_header("accept", "application/json")
         |> get("/api/pleroma/admin/users/tag")
-        |> json_response(200)
+        |> json_response_and_validate_schema(200)
 
       assert [
                "mrf_tag:disable-any-subscription",