diff --git a/assets/js/hooks/chessBoard.js b/assets/js/hooks/chessBoard.js
index 68f796c..5270610 100644
--- a/assets/js/hooks/chessBoard.js
+++ b/assets/js/hooks/chessBoard.js
@@ -4,11 +4,70 @@ import { Chess } from "chess.js";
 export const ChessBoard = {
   mounted() {
     this.chess = new Chess();
+    this.ground = null;
+
+    this.handleEvent("init_board", (payload) => {
+      this.initBoard(payload);
+    });
+
+    this.handleEvent("set_fen", ({ fen }) => {
+      try {
+        this.chess.load(fen);
+
+        if (this.ground) {
+          const currentTurnColor = this.chess.turn() === "w" ? "white" : "black";
+          this.ground.set({
+            fen: fen,
+            turnColor: currentTurnColor,
+            movable: {
+              color: currentTurnColor,
+              dests: this.getValidDests(),
+            },
+          });
+        } else {
+          this.initBoard({
+            fen,
+            orientation: "white",
+            player_color: "white",
+          });
+        }
+      } catch (error) {
+        console.error("Invalid FEN string submitted:", error);
+        alert("Invalid FEN configuration!");
+      }
+    });
+
+    this.initBoard({
+      fen: this.chess.fen(),
+      orientation: "white",
+      player_color: "white",
+    });
+  },
+
+  initBoard({ fen, orientation, player_color }) {
+    try {
+      this.chess.load(fen);
+    } catch (error) {
+      console.error("Invalid FEN from server:", fen, error);
+      this.pushEvent("chess_fen_invalid", {
+        fen: fen,
+        message: error && error.message ? error.message : String(error),
+      });
+      return;
+    }
+
+    if (this.ground) {
+      this.ground.destroy();
+    }
+
+    const turnColor = this.chess.turn() === "w" ? "white" : "black";
 
     this.ground = Chessground(this.el, {
-      fen: this.chess.fen(),
+      fen: fen,
+      orientation: orientation,
+      turnColor: turnColor,
       movable: {
-        color: "white",
+        color: player_color,
         free: false,
         dests: this.getValidDests(),
       },
@@ -18,26 +77,6 @@ export const ChessBoard = {
         },
       },
     });
-
-    this.handleEvent("set_fen", ({ fen }) => {
-      try {
-        this.chess.load(fen);
-
-        const currentTurnColor = this.chess.turn() === "w" ? "white" : "black";
-
-        this.ground.set({
-          fen: fen,
-          turnColor: currentTurnColor,
-          movable: {
-            color: currentTurnColor,
-            dests: this.getValidDests(),
-          },
-        });
-      } catch (error) {
-        console.error("Invalid FEN string submitted:", error);
-        alert("Invalid FEN configuration!");
-      }
-    });
   },
 
   getValidDests() {
@@ -56,7 +95,7 @@ export const ChessBoard = {
     const destRank = dest[1];
     if (piece?.role === "pawn" && (destRank === "1" || destRank === "8")) {
       this.showPromotionDialog(orig, dest);
-      return; // don't execute yet — wait for user choice
+      return;
     }
     this.executeMove(orig, dest);
   },
@@ -98,12 +137,23 @@ export const ChessBoard = {
     const move = this.chess.move({ from: orig, to: dest, promotion });
 
     if (move) {
-      this.pushEvent("move_played", {
+      const eventName =
+        this.el.dataset && this.el.dataset.endgameId
+          ? "endgame_move_played"
+          : "move_played";
+
+      const payload = {
         from: orig,
         to: dest,
         fen: this.chess.fen(),
         san: move.san,
-      });
+      };
+
+      if (eventName === "endgame_move_played") {
+        payload.endgame_id = this.el.dataset.endgameId;
+      }
+
+      this.pushEvent(eventName, payload);
 
       const nextTurnColor = this.chess.turn() === "w" ? "white" : "black";
 
diff --git a/lib/chesstrainer/endgames/endgame.ex b/lib/chesstrainer/endgames/endgame.ex
index 65a79d9..cc87a34 100644
--- a/lib/chesstrainer/endgames/endgame.ex
+++ b/lib/chesstrainer/endgames/endgame.ex
@@ -36,6 +36,78 @@ defmodule Chesstrainer.Endgames.Endgame do
     |> validate_format(:key, ~r/^(?=.{5,10}$)KQ*R*[NB]*P*\sv\sKQ*R*[NB]*P*$/,
       message: "Key must follow pattern KQ.. v KQR.., max pieces 7"
     )
+    |> validate_change(:fen, fn :fen, fen ->
+      case fen_issues(fen) do
+        [] -> []
+        issues -> [fen: "is not a valid FEN: #{Enum.join(issues, "; ")}"]
+      end
+    end)
     |> unique_constraint(:fen, message: "FEN already exists")
   end
+
+  # Strict structural validation. Mirrors chess.js rules so the FEN survives
+  # both the server-side parser (Chex, permissive) and the client-side parser
+  # (chess.js, strict).
+  defp fen_issues(fen) do
+    case String.split(fen, " ") do
+      [board, active, _castling, _en_passant, halfmove, fullmove] ->
+        issues = []
+
+        issues =
+          if valid_board?(board),
+            do: issues,
+            else: ["board must be 8 ranks of 8 squares each"]
+
+        issues =
+          if active in ["w", "b"],
+            do: issues,
+            else: ["active color must be 'w' or 'b'"]
+
+        issues =
+          if non_negative_integer?(halfmove),
+            do: issues,
+            else: ["halfmove clock must be a non-negative integer"]
+
+        issues =
+          if positive_integer?(fullmove),
+            do: issues,
+            else: ["fullmove number must be a positive integer"]
+
+        issues
+
+      _ ->
+        ["must have 6 space-separated fields"]
+    end
+  end
+
+  defp valid_board?(board) do
+    ranks = String.split(board, "/")
+
+    length(ranks) == 8 and Enum.all?(ranks, &valid_rank?/1)
+  end
+
+  defp valid_rank?(rank) do
+    squares =
+      rank
+      |> String.graphemes()
+      |> Enum.reduce(0, fn
+        g, acc when byte_size(g) == 1 ->
+          c = :binary.first(g)
+
+          if c >= ?1 and c <= ?8 do
+            acc + (c - ?0)
+          else
+            acc + 1
+          end
+      end)
+
+    squares == 8
+  end
+
+  defp non_negative_integer?(str), do: integer_string?(str) and String.to_integer(str) >= 0
+  defp positive_integer?(str), do: integer_string?(str) and String.to_integer(str) >= 1
+
+  defp integer_string?(str) do
+    Regex.match?(~r/^[0-9]+$/, str)
+  end
 end
diff --git a/lib/chesstrainer/tags.ex b/lib/chesstrainer/tags.ex
index 42c1efc..27d099a 100644
--- a/lib/chesstrainer/tags.ex
+++ b/lib/chesstrainer/tags.ex
@@ -101,4 +101,23 @@ defmodule Chesstrainer.Tags do
   def change_tag(%Tag{} = tag, attrs \\ %{}) do
     Tag.changeset(tag, attrs)
   end
+
+  def search("", _category), do: []
+
+  def search(query, category) when is_binary(query) do
+    pattern = "%#{query}%"
+
+    Tag
+    |> where([t], ilike(t.name, ^pattern) and t.category == ^category)
+    |> order_by([t], asc: t.name)
+    |> limit(20)
+    |> Repo.all()
+  end
+
+  def get_or_create(name, category) when is_binary(name) do
+    case Repo.get_by(Tag, name: name, category: category) do
+      nil -> create_tag(%{name: name, category: category})
+      tag -> {:ok, tag}
+    end
+  end
 end
diff --git a/lib/chesstrainer_web/live/endgame_live/index.ex b/lib/chesstrainer_web/live/endgame_live/index.ex
index 91a5fc9..0de26bf 100644
--- a/lib/chesstrainer_web/live/endgame_live/index.ex
+++ b/lib/chesstrainer_web/live/endgame_live/index.ex
@@ -34,6 +34,7 @@ defmodule ChesstrainerWeb.EndgameLive.Index do
           <div class="sr-only">
             <.link navigate={~p"/admin/endgames/#{endgame}"}>Show</.link>
           </div>
+          <.link navigate={~p"/endgames/#{endgame}/play"}>Play</.link>
           <.link navigate={~p"/admin/endgames/#{endgame}/edit"}>Edit</.link>
         </:action>
         <:action :let={{id, endgame}}>
diff --git a/lib/chesstrainer_web/live/endgame_live/play.ex b/lib/chesstrainer_web/live/endgame_live/play.ex
new file mode 100644
index 0000000..cca5edf
--- /dev/null
+++ b/lib/chesstrainer_web/live/endgame_live/play.ex
@@ -0,0 +1,119 @@
+defmodule ChesstrainerWeb.EndgameLive.Play do
+  use ChesstrainerWeb, :live_view
+
+  alias Chesstrainer.Endgames
+
+  @impl true
+  def render(assigns) do
+    ~H"""
+    <Layouts.app flash={@flash}>
+      <.header>
+        Play endgame {@endgame.key}
+        <:subtitle>
+          {@endgame.color} to move · Result: {@endgame.result} · Rating: {@endgame.rating}
+        </:subtitle>
+        <:actions>
+          <.button navigate={~p"/endgames"}>
+            <.icon name="hero-arrow-left" /> Back to endgames
+          </.button>
+        </:actions>
+      </.header>
+
+      <div class="bg-gray-100 p-4 rounded mb-4 flex justify-between items-center shadow-sm">
+        <div>
+          <p class="text-sm text-gray-600 font-semibold">Last Played Move:</p>
+          <p class="text-lg font-mono text-blue-600">{@last_from_to}</p>
+          <p class="text-lg font-mono text-blue-600">{@last_san}</p>
+          <p class="text-lg font-mono text-emerald-600">
+            {if @move_list == [] do
+              "No Moves"
+            else
+              Enum.reverse(@move_list) |> Enum.join(", ")
+            end}
+          </p>
+        </div>
+        <div>
+          <.button phx-click="reset" variant="primary">
+            <.icon name="hero-arrow-path" /> Reset
+          </.button>
+        </div>
+      </div>
+
+      <div class="flex justify-center bg-gray-200 p-4 rounded-xl shadow-inner">
+        <div
+          id="endgame-board"
+          phx-hook="ChessBoard"
+          phx-update="ignore"
+          data-endgame-id={@endgame.id}
+          class="w-[400px] h-[400px]"
+        >
+        </div>
+      </div>
+
+      <.list>
+        <:item title="Fen">{@endgame.fen}</:item>
+        <:item title="Key">{@endgame.key}</:item>
+        <:item title="Color">{@endgame.color}</:item>
+        <:item title="Result">{@endgame.result}</:item>
+        <:item title="Rating">{@endgame.rating}</:item>
+      </.list>
+    </Layouts.app>
+    """
+  end
+
+  @impl true
+  def mount(%{"id" => id}, _session, socket) do
+    endgame = Endgames.get_endgame!(id)
+
+    socket =
+      socket
+      |> assign(:page_title, "Play endgame")
+      |> assign(:endgame, endgame)
+      |> assign(:move_list, [])
+      |> assign(:last_san, "None yet")
+      |> assign(:last_from_to, "None yet")
+      |> push_event("init_board", %{
+        fen: endgame.fen,
+        orientation: Atom.to_string(endgame.color),
+        player_color: Atom.to_string(endgame.color)
+      })
+
+    {:ok, socket}
+  end
+
+  @impl true
+  def handle_event(
+        "endgame_move_played",
+        %{"from" => from, "to" => to, "san" => san},
+        socket
+      ) do
+    # TODO: server-side legality check + tablebase evaluation when wired
+    {:noreply,
+     socket
+     |> assign(:last_from_to, "#{from} ➔ #{to}")
+     |> assign(:last_san, san)
+     |> assign(:move_list, [san | socket.assigns.move_list])}
+  end
+
+  def handle_event("chess_fen_invalid", %{"fen" => fen, "message" => message}, socket) do
+    {:noreply,
+     put_flash(
+       socket,
+       :error,
+       "Endgame FEN is invalid and the board cannot be loaded: #{message} (#{fen})"
+     )}
+  end
+
+  def handle_event("reset", _params, socket) do
+    {:noreply,
+     socket
+     |> assign(:move_list, [])
+     |> assign(:last_san, "None yet")
+     |> assign(:last_from_to, "None yet")
+     |> push_event("init_board", %{
+       fen: socket.assigns.endgame.fen,
+       orientation: Atom.to_string(socket.assigns.endgame.color),
+       player_color: Atom.to_string(socket.assigns.endgame.color)
+     })}
+  end
+end
diff --git a/lib/chesstrainer_web/live/endgame_live/player_index.ex b/lib/chesstrainer_web/live/endgame_live/player_index.ex
new file mode 100644
index 0000000..4311f9a
--- /dev/null
+++ b/lib/chesstrainer_web/live/endgame_live/player_index.ex
@@ -0,0 +1,38 @@
+defmodule ChesstrainerWeb.EndgameLive.PlayerIndex do
+  use ChesstrainerWeb, :live_view
+
+  alias Chesstrainer.Endgames
+
+  @impl true
+  def render(assigns) do
+    ~H"""
+    <Layouts.app flash={@flash}>
+      <.header>
+        Endgames
+        <:subtitle>Pick an endgame to play.</:subtitle>
+      </.header>
+
+      <.table
+        id="player-endgames"
+        rows={@streams.endgames}
+      >
+        <:col :let={{_id, endgame}} label="Key">{endgame.key}</:col>
+        <:col :let={{_id, endgame}} label="Color">{endgame.color}</:col>
+        <:col :let={{_id, endgame}} label="Result">{endgame.result}</:col>
+        <:col :let={{_id, endgame}} label="Rating">{endgame.rating}</:col>
+        <:action :let={{_id, endgame}}>
+          <.link navigate={~p"/endgames/#{endgame}/play"}>Play</.link>
+        </:action>
+      </.table>
+    </Layouts.app>
+    """
+  end
+
+  @impl true
+  def mount(_params, _session, socket) do
+    {:ok,
+     socket
+     |> assign(:page_title, "Endgames")
+     |> stream(:endgames, Endgames.list_endgames())}
+  end
+end
diff --git a/lib/chesstrainer_web/live/endgame_live/show.ex b/lib/chesstrainer_web/live/endgame_live/show.ex
index c5d6811..3900adb 100644
--- a/lib/chesstrainer_web/live/endgame_live/show.ex
+++ b/lib/chesstrainer_web/live/endgame_live/show.ex
@@ -31,6 +31,9 @@ defmodule ChesstrainerWeb.EndgameLive.Show do
           <.button navigate={~p"/admin/endgames"}>
             <.icon name="hero-arrow-left" />
           </.button>
+          <.button navigate={~p"/endgames/#{@endgame}/play"}>
+            <.icon name="hero-play" /> Play (opens trainer)
+          </.button>
           <.button variant="primary" navigate={~p"/admin/endgames/#{@endgame}/edit?return_to=show"}>
             <.icon name="hero-pencil-square" /> Edit endgame
           </.button>
diff --git a/lib/chesstrainer_web/router.ex b/lib/chesstrainer_web/router.ex
index 59fb058..beb9017 100644
--- a/lib/chesstrainer_web/router.ex
+++ b/lib/chesstrainer_web/router.ex
@@ -20,6 +20,9 @@ defmodule ChesstrainerWeb.Router do
     get "/", PageController, :home
 
     live "/chess-test", ChessTestLive
+
+    live "/endgames", EndgameLive.PlayerIndex, :index
+    live "/endgames/:id/play", EndgameLive.Play, :play
   end
 
   scope "/admin", ChesstrainerWeb do
diff --git a/priv/repo/seeds.exs b/priv/repo/seeds.exs
index 179b8af..ab718a6 100644
--- a/priv/repo/seeds.exs
+++ b/priv/repo/seeds.exs
@@ -32,7 +32,7 @@ Repo.insert_all(Endgame, [
   },
   %{
     id: Ecto.UUID.generate(),
-    fen: "6k1/5p2/6p1/8/7p/8/6PP/6K1 b - - 0 0",
+    fen: "6k1/5p2/6p1/8/7p/8/6PP/6K1 b - - 0 1",
     color: :black,
     key: "KPPP v KPP",
     message: "3 pawns vs 2 pawns",
diff --git a/test/chesstrainer/endgames_test.exs b/test/chesstrainer/endgames_test.exs
new file mode 100644
index 0000000..9e4d9dd
--- /dev/null
+++ b/test/chesstrainer/endgames_test.exs
@@ -0,0 +1,76 @@
+defmodule Chesstrainer.EndgamesTest do
+  use Chesstrainer.DataCase
+
+  alias Chesstrainer.Endgames
+  alias Chesstrainer.Endgames.Endgame
+
+  describe "create_endgame/1 FEN validation" do
+    test "accepts a standard valid FEN" do
+      attrs = %{
+        fen: "8/8/3k4/8/8/3K1R2/8/8 w - - 0 1",
+        color: :white,
+        key: "KR v K",
+        result: :win,
+        rating: 1500
+      }
+
+      assert {:ok, %Endgame{}} = Endgames.create_endgame(attrs)
+    end
+
+    test "rejects a FEN with fullmove number zero" do
+      attrs = %{
+        fen: "6k1/5p2/6p1/8/7p/8/6PP/6K1 b - - 0 0",
+        color: :black,
+        key: "KPPP v KPP",
+        result: :win,
+        rating: 1500
+      }
+
+      assert {:error, changeset} = Endgames.create_endgame(attrs)
+      assert [msg] = errors_on(changeset).fen
+      assert msg =~ "fullmove number"
+    end
+
+    test "rejects a FEN with a zero digit in a rank" do
+      attrs = %{
+        fen: "4k3/8/8/8/8/8/8/0K7 w - - 0 1",
+        color: :white,
+        key: "KQ v K",
+        result: :win,
+        rating: 1500
+      }
+
+      assert {:error, changeset} = Endgames.create_endgame(attrs)
+      assert [msg] = errors_on(changeset).fen
+      assert msg =~ "board must be 8 ranks"
+    end
+
+    test "rejects a FEN with the wrong number of fields" do
+      attrs = %{
+        fen: "8/8/3k4/8/8/3K1R2/8/8",
+        color: :white,
+        key: "KQ v K",
+        result: :win,
+        rating: 1500
+      }
+
+      assert {:error, changeset} = Endgames.create_endgame(attrs)
+      assert [msg] = errors_on(changeset).fen
+      assert msg =~ "6 space-separated"
+    end
+
+    test "rejects a FEN with an unknown active color" do
+      attrs = %{
+        fen: "8/8/3k4/8/8/3K1R2/8/8 x - - 0 1",
+        color: :white,
+        key: "KQ v K",
+        result: :win,
+        rating: 1500
+      }
+
+      assert {:error, changeset} = Endgames.create_endgame(attrs)
+      assert [msg] = errors_on(changeset).fen
+      assert msg =~ "active color"
+    end
+  end
+end
diff --git a/test/chesstrainer_web/live/endgame_live/play_test.exs b/test/chesstrainer_web/live/endgame_live/play_test.exs
new file mode 100644
index 0000000..b55951a
--- /dev/null
+++ b/test/chesstrainer_web/live/endgame_live/play_test.exs
@@ -0,0 +1,115 @@
+defmodule ChesstrainerWeb.EndgameLive.PlayTest do
+  use ChesstrainerWeb.ConnCase
+
+  import Phoenix.LiveViewTest
+  import Chesstrainer.EndgamesFixtures
+
+  defp assert_init_board(view, expected_fen, expected_orientation, expected_player_color) do
+    %{proxy: {ref, _topic, _}} = view
+
+    assert_receive {^ref, {:push_event, "init_board", payload}}, 100
+
+    assert payload.fen == expected_fen
+    assert payload.orientation == expected_orientation
+    assert payload.player_color == expected_player_color
+  end
+
+  describe "mount" do
+    test "renders the chessboard hook div and pushes init_board", %{conn: conn} do
+      endgame = endgame_fixture(color: :white)
+
+      {:ok, view, _html} = live(conn, ~p"/endgames/#{endgame}/play")
+
+      assert has_element?(view, "#endgame-board")
+      assert_init_board(view, endgame.fen, "white", "white")
+    end
+
+    test "pushes black orientation when the endgame color is black", %{conn: conn} do
+      endgame = endgame_fixture(color: :black)
+
+      {:ok, view, _html} = live(conn, ~p"/endgames/#{endgame}/play")
+
+      assert_init_board(view, endgame.fen, "black", "black")
+    end
+
+    test "shows endgame metadata in the header", %{conn: conn} do
+      endgame = endgame_fixture(key: "KQ v K", color: :white, result: :win, rating: 1800)
+
+      {:ok, _view, html} = live(conn, ~p"/endgames/#{endgame}/play")
+
+      assert html =~ "KQ v K"
+      assert html =~ "white to move"
+      assert html =~ "win"
+      assert html =~ "1800"
+    end
+
+    test "raises when the endgame does not exist", %{conn: conn} do
+      assert_raise Ecto.NoResultsError, fn ->
+        live(conn, ~p"/endgames/00000000-0000-0000-0000-000000000000/play")
+      end
+    end
+  end
+
+  describe "chess_fen_invalid" do
+    test "shows a flash when the chessground hook reports an unparseable FEN", %{conn: conn} do
+      endgame = endgame_fixture()
+
+      {:ok, view, _html} = live(conn, ~p"/endgames/#{endgame}/play")
+
+      view
+      |> render_hook("chess_fen_invalid", %{
+        "fen" => endgame.fen,
+        "message" => "Invalid FEN: move number must be a positive integer"
+      })
+
+      html = render(view)
+      assert html =~ "Endgame FEN is invalid"
+      assert html =~ "move number must be a positive integer"
+    end
+  end
+
+  describe "endgame_move_played" do
+    test "appends the SAN move and updates last_san / last_from_to", %{conn: conn} do
+      endgame = endgame_fixture()
+
+      {:ok, view, _html} = live(conn, ~p"/endgames/#{endgame}/play")
+
+      view
+      |> render_hook("endgame_move_played", %{
+        "from" => "d1",
+        "to" => "d7",
+        "san" => "Qd7+",
+        "fen" => endgame.fen,
+        "endgame_id" => endgame.id
+      })
+
+      html = render(view)
+      assert html =~ "Qd7+"
+      assert html =~ "d1 ➔ d7"
+    end
+  end
+
+  describe "reset" do
+    test "clears move list and re-pushes init_board", %{conn: conn} do
+      endgame = endgame_fixture()
+
+      {:ok, view, _html} = live(conn, ~p"/endgames/#{endgame}/play")
+
+      view
+      |> render_hook("endgame_move_played", %{
+        "from" => "d1",
+        "to" => "d7",
+        "san" => "Qd7+",
+        "fen" => endgame.fen,
+        "endgame_id" => endgame.id
+      })
+
+      assert render(view) =~ "Qd7+"
+
+      view |> element("button", "Reset") |> render_click()
+
+      assert render(view) =~ "No Moves"
+      assert_init_board(view, endgame.fen, "white", "white")
+    end
+  end
+end
diff --git a/test/chesstrainer_web/live/endgame_live/player_index_test.exs b/test/chesstrainer_web/live/endgame_live/player_index_test.exs
new file mode 100644
index 0000000..848ebae
--- /dev/null
+++ b/test/chesstrainer_web/live/endgame_live/player_index_test.exs
@@ -0,0 +1,28 @@
+defmodule ChesstrainerWeb.EndgameLive.PlayerIndexTest do
+  use ChesstrainerWeb.ConnCase
+
+  import Phoenix.LiveViewTest
+  import Chesstrainer.EndgamesFixtures
+
+  test "lists endgames with a play link per row", %{conn: conn} do
+    endgame = endgame_fixture()
+    other = endgame_fixture()
+
+    {:ok, _view, html} = live(conn, ~p"/endgames")
+
+    assert html =~ "Endgames"
+    assert html =~ endgame.key
+    assert html =~ other.key
+    assert html =~ ~p"/endgames/#{endgame}/play"
+    assert html =~ ~p"/endgames/#{other}/play"
+  end
+
+  test "navigating to a play page renders the board", %{conn: conn} do
+    endgame = endgame_fixture()
+
+    {:ok, view, _html} = live(conn, ~p"/endgames/#{endgame}/play")
+
+    assert has_element?(view, "#endgame-board")
+    assert has_element?(view, ~s{a[href="/endgames"]})
+  end
+end
diff --git a/test/support/fixtures/endgame_fixtures.ex b/test/support/fixtures/endgame_fixtures.ex
new file mode 100644
index 0000000..0876a5c
--- /dev/null
+++ b/test/support/fixtures/endgame_fixtures.ex
@@ -0,0 +1,44 @@
+defmodule Chesstrainer.EndgamesFixtures do
+  @moduledoc """
+  This module defines test helpers for creating
+  entities via the `Chesstrainer.Endgames` context.
+  """
+
+  @doc """
+  Generate a unique endgame FEN.
+
+  Endgames have a unique constraint on :fen, so tests need
+  distinct FENs when inserting more than one. Each call
+  shifts the white king's file to avoid FEN collisions.
+  """
+  def unique_endgame_fen do
+    # White king on rank 1 in columns b..g, leaving 1-6 empty squares
+    # before and 6-1 after. Both before_king and after_king are valid
+    # single digits (1-8), and the rank sums to 8.
+    offset = System.unique_integer([:positive]) |> rem(6)
+    before_king = offset + 1
+    after_king = 7 - before_king
+    "4k3/8/8/8/8/8/8/#{before_king}K#{after_king} w - - 0 1"
+  end
+
+  @doc """
+  Generate an endgame.
+
+  A simple K v K position with a unique FEN, color,
+  key, rating, and result.
+  """
+  def endgame_fixture(attrs \\ %{}) do
+    {:ok, endgame} =
+      attrs
+      |> Enum.into(%{
+        fen: unique_endgame_fen(),
+        key: "KQ v K",
+        color: :white,
+        result: :win,
+        rating: 1500
+      })
+      |> Chesstrainer.Endgames.create_endgame()
+
+    endgame
+  end
+end