diff --git a/src/main.zig b/src/main.zig
index bea3bb7..7b64032 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -23,6 +23,8 @@ const GameState = struct {
     discard_pile: std.ArrayListUnmanaged(Card),
     hands: []std.ArrayListUnmanaged(Card),
 
+    marked_cards: std.AutoHashMapUnmanaged(Card, void),
+
     pub fn init(allocator: std.mem.Allocator, seed: u64, num_players: usize) !@This() {
         var draw_pile = std.ArrayListUnmanaged(Card).fromOwnedSlice(try makeStandardDeck(allocator));
         errdefer draw_pile.deinit(allocator);
@@ -59,6 +61,7 @@ const GameState = struct {
             .draw_pile = draw_pile,
             .discard_pile = discard_pile,
             .hands = hands,
+            .marked_cards = .{},
         };
     }
 
@@ -69,6 +72,7 @@ const GameState = struct {
             hand.deinit(this.allocator);
         }
         this.allocator.free(this.hands);
+        this.marked_cards.deinit(this.allocator);
     }
 
     pub fn clone(this: @This(), allocator: std.mem.Allocator) !@This() {
@@ -84,6 +88,7 @@ const GameState = struct {
             .draw_pile = try this.draw_pile.clone(allocator),
             .discard_pile = try this.discard_pile.clone(allocator),
             .hands = hands,
+            .marked_cards = try this.marked_cards.clone(allocator),
         };
     }
 };
@@ -262,6 +267,9 @@ pub fn main() !void {
                         history.clearRetainingCapacity();
                     }
                     try history.append(try transition.game_state.clone(gpa.allocator()));
+
+                    if (request_command) |command| gpa.allocator().free(command);
+                    request_command = null;
                 },
             }
         }
@@ -734,13 +742,14 @@ pub const CardElement = struct {
     allocator: std.mem.Allocator,
     visual: Visual,
     command: ?[]const u8,
+    marked: bool,
 
     const Visual = union(enum) {
         back,
         card: Card,
     };
 
-    pub fn create(allocator: std.mem.Allocator, options: struct { visual: Visual, command: ?[]const u8 }) !*@This() {
+    pub fn create(allocator: std.mem.Allocator, options: struct { visual: Visual, command: ?[]const u8, marked: ?bool = null }) !*@This() {
         const this = try allocator.create(@This());
         errdefer allocator.destroy(this);
 
@@ -748,6 +757,7 @@ pub const CardElement = struct {
             .allocator = allocator,
             .visual = options.visual,
             .command = options.command,
+            .marked = options.marked orelse false,
         };
         return this;
     }
@@ -776,24 +786,32 @@ pub const CardElement = struct {
     pub fn element_render(pointer: ?*anyopaque, canvas: *seizer.Canvas, render_resources: RenderResources, min: [2]f32, max: [2]f32) void {
         const this: *@This() = @ptrCast(@alignCast(pointer));
 
+        const mark_offset = if (this.marked)
+            [2]f32{
+                0,
+                @as(f32, @floatFromInt(render_resources.deck.tilesheet.tile_size[1])) * -0.4,
+            }
+        else
+            [2]f32{ 0, 0 };
+
         switch (this.visual) {
             .back => render_resources.deck.tilesheet.renderTile(
                 canvas,
                 render_resources.deck.back,
-                .{ min[0], min[1] },
+                .{ min[0] + mark_offset[0], min[1] + mark_offset[1] },
                 .{},
             ),
             .card => |card| render_resources.deck.tilesheet.renderTile(
                 canvas,
                 render_resources.deck.getTileForCard(card),
-                .{ min[0], min[1] },
+                .{ min[0] + mark_offset[0], min[1] + mark_offset[1] },
                 .{},
             ),
         }
 
         if (render_resources.hovered != null and this.command != null and std.mem.eql(u8, render_resources.hovered.?, this.command.?)) {
             canvas.rect(
-                min,
+                .{ min[0] + mark_offset[0], min[1] + mark_offset[1] },
                 .{ max[0] - min[0], max[1] - min[1] },
                 .{ .color = .{ 0xAA, 0xFF, 0xAA, 0x60 } },
             );
@@ -867,6 +885,33 @@ fn drawCardHandler(arena: std.mem.Allocator, request: Request) HandlerError!Resp
 }
 
 fn playerTurnHandler(arena: std.mem.Allocator, request: Request) HandlerError!Response {
+    if (request.command) |command| handle_command: {
+        if (std.mem.startsWith(u8, command, "mark ")) {
+            var iter = std.mem.tokenizeScalar(u8, command, ' ');
+            _ = iter.next() orelse break :handle_command;
+            const rank_str = iter.next() orelse break :handle_command;
+            _ = iter.next() orelse break :handle_command;
+            const suit_str = iter.next() orelse break :handle_command;
+
+            const card = Card{
+                .suit = std.meta.stringToEnum(assets.Suit, suit_str) orelse break :handle_command,
+                .rank = std.fmt.parseInt(u4, rank_str, 10) catch break :handle_command,
+            };
+
+            var new_game_state = try request.game_state.clone(arena);
+            if (new_game_state.marked_cards.contains(card)) {
+                _ = new_game_state.marked_cards.remove(card);
+            } else {
+                try new_game_state.marked_cards.put(arena, card, {});
+            }
+
+            return Response{ .transition = .{
+                .game_state = new_game_state,
+                .can_undo = true,
+            } };
+        }
+    }
+
     var draw_pile = try Pile.create(arena, request.game_state.draw_pile.items);
     draw_pile.hidden = true;
 
@@ -876,7 +921,8 @@ fn playerTurnHandler(arena: std.mem.Allocator, request: Request) HandlerError!Re
     for (request.game_state.hands[0].items) |card| {
         var card_element = try CardElement.create(arena, .{
             .visual = .{ .card = card },
-            .command = "mark",
+            .command = try std.fmt.allocPrint(arena, "mark {} of {s}", .{ card.rank, @tagName(card.suit) }),
+            .marked = request.game_state.marked_cards.contains(card),
         });
         try hand.addElement(card_element.element());
     }