diff --git a/src/ClaudeDo.Worker/External/ExternalMcpService.cs b/src/ClaudeDo.Worker/External/ExternalMcpService.cs
index 4f79363..f1687d9 100644
--- a/src/ClaudeDo.Worker/External/ExternalMcpService.cs
+++ b/src/ClaudeDo.Worker/External/ExternalMcpService.cs
@@ -130,6 +130,33 @@ public sealed class ExternalMcpService
         return ToDto(entity);
     }
 
+    [McpServerTool, Description("Update an existing task's title, description, commit type, and/or tags. Pass null to leave a field unchanged. Tags are replaced as a full set when non-null. Refuses if the task is currently Running.")]
+    public async Task<TaskDto> UpdateTask(
+        string taskId,
+        string? title,
+        string? description,
+        string? commitType,
+        IReadOnlyList<string>? tags,
+        CancellationToken cancellationToken)
+    {
+        var task = await _tasks.GetByIdAsync(taskId, cancellationToken)
+            ?? throw new InvalidOperationException($"Task {taskId} not found.");
+        if (task.Status == TaskStatus.Running)
+            throw new InvalidOperationException("Cannot update a running task. Cancel it first.");
+
+        if (title is not null) task.Title = title;
+        if (description is not null) task.Description = description;
+        if (commitType is not null) task.CommitType = commitType;
+        await _tasks.UpdateAsync(task, cancellationToken);
+
+        if (tags is not null)
+            await _tasks.SetTagsAsync(taskId, tags, cancellationToken);
+
+        var reload = (await _tasks.GetByIdAsync(taskId, cancellationToken))!;
+        await _broadcaster.TaskUpdated(taskId);
+        return ToDto(reload);
+    }
+
     [McpServerTool, Description("Update a task's status. Only 'Manual' and 'Queued' are permitted — use RunTaskNow or CancelTask for execution control.")]
     public async Task<TaskDto> UpdateTaskStatus(
         string taskId,
diff --git a/tests/ClaudeDo.Worker.Tests/External/ExternalMcpServiceTests.cs b/tests/ClaudeDo.Worker.Tests/External/ExternalMcpServiceTests.cs
index 9a5ed11..9a4b6d4 100644
--- a/tests/ClaudeDo.Worker.Tests/External/ExternalMcpServiceTests.cs
+++ b/tests/ClaudeDo.Worker.Tests/External/ExternalMcpServiceTests.cs
@@ -172,4 +172,57 @@ public sealed class ExternalMcpServiceTests : IDisposable
 
         Assert.Empty(await _tasks.GetTagsAsync(dto.Id));
     }
+
+    [Fact]
+    public async Task UpdateTask_PatchesNonNullFieldsOnly()
+    {
+        var listId = await SeedListAsync();
+        var task = await SeedTaskAsync(listId, "old title");
+        var queue = CreateQueue();
+        var sut = BuildSut(queue);
+
+        var dto = await sut.UpdateTask(task.Id, "new title", null, null, null, CancellationToken.None);
+
+        Assert.Equal("new title", dto.Title);
+        var loaded = await _tasks.GetByIdAsync(task.Id);
+        Assert.Equal("new title", loaded!.Title);
+    }
+
+    [Fact]
+    public async Task UpdateTask_TagsReplaceFullSet()
+    {
+        var listId = await SeedListAsync();
+        var task = await SeedTaskAsync(listId);
+        await _tasks.SetTagsAsync(task.Id, new[] { "agent" });
+        var queue = CreateQueue();
+        var sut = BuildSut(queue);
+
+        await sut.UpdateTask(task.Id, null, null, null, new[] { "manual" }, CancellationToken.None);
+
+        var tags = await _tasks.GetTagsAsync(task.Id);
+        Assert.Single(tags);
+        Assert.Equal("manual", tags[0].Name);
+    }
+
+    [Fact]
+    public async Task UpdateTask_OnRunning_Throws()
+    {
+        var listId = await SeedListAsync();
+        var task = await SeedTaskAsync(listId, status: TaskStatus.Running);
+        var queue = CreateQueue();
+        var sut = BuildSut(queue);
+
+        await Assert.ThrowsAsync<InvalidOperationException>(() =>
+            sut.UpdateTask(task.Id, "x", null, null, null, CancellationToken.None));
+    }
+
+    [Fact]
+    public async Task UpdateTask_NotFound_Throws()
+    {
+        var queue = CreateQueue();
+        var sut = BuildSut(queue);
+
+        await Assert.ThrowsAsync<InvalidOperationException>(() =>
+            sut.UpdateTask("does-not-exist", "x", null, null, null, CancellationToken.None));
+    }
 }