MCP Todo

Instructions

Implementation Reference

• src/server.ts:95-111 (handler)

  Executes the toggle_todo tool: loads todos, finds the todo by ID, flips its 'done' status, saves the list, and returns a confirmation or error message.

  async ({ id }) => {
    const todos = await readTodos();
    const i = todos.findIndex((t) => t.id === id);
    if (i === -1)
      return { content: [{ type: "text", text: `No todo with id ${id}` }] };
    const todo = todos[i]!;
    todo.done = !todo.done;
    await writeTodos(todos);
    return {
      content: [
        {
          type: "text",
          text: `Toggled #${id} to ${todo.done ? "done" : "not done"}`,
        },
      ],
    };
  }

• src/server.ts:90-94 (schema)

  Tool metadata and input schema for toggle_todo: requires a positive integer 'id'.

  {
    title: "Toggle Todo",
    description: "Toggle a todo by id",
    inputSchema: { id: z.number().int().positive() },
  },

• src/server.ts:88-112 (registration)

  Registers the toggle_todo tool on the MCP server with schema and handler function.

  server.registerTool(
    "toggle_todo",
    {
      title: "Toggle Todo",
      description: "Toggle a todo by id",
      inputSchema: { id: z.number().int().positive() },
    },
    async ({ id }) => {
      const todos = await readTodos();
      const i = todos.findIndex((t) => t.id === id);
      if (i === -1)
        return { content: [{ type: "text", text: `No todo with id ${id}` }] };
      const todo = todos[i]!;
      todo.done = !todo.done;
      await writeTodos(todos);
      return {
        content: [
          {
            type: "text",
            text: `Toggled #${id} to ${todo.done ? "done" : "not done"}`,
          },
        ],
      };
    }
  );

• src/server.ts:20-30 (helper)

  Helper functions readTodos and writeTodos for loading and saving the todo list from/to JSON file, used by the toggle_todo handler.

  async function readTodos(): Promise<Todo[]> {
    try {
      const s = await fs.readFile(DB_PATH, "utf-8");
      return JSON.parse(s);
    } catch {
      return [];
    }
  }
  async function writeTodos(todos: Todo[]) {
    await fs.writeFile(DB_PATH, JSON.stringify(todos, null, 2), "utf-8");
  }