**TodoWriteTool: To-Do List**

TodoWriteTool is Claude Code's classic lightweight task management tool.
Its purpose isn't to replace a formal task system, but to allow the model to break down work into a visible sequence of todos within the current session.

You can think of it as:

• TodoWriteTool: Lightweight, in-session, quick tracking
• TaskCreateTool series: Structured, formal task system

tools/TodoWriteTool/TodoWriteTool.ts:

const inputSchema = z.strictObject({
  todos: TodoListSchema().describe('The updated todo list'),
})

The actual state write-back is:

context.setAppState(prev => ({
  ...prev,
  todos: {
    ...prev.todos,
    [todoKey]: newTodos,
  },
}))

This shows that it's essentially an AppState writing tool.

Model splits current work > TodoWriteTool > Updates AppState.todos > UI displays checklist > Model proceeds to next step according to the list

It has two interesting design features:

1. When all todos are completed, the list is directly cleared
2. If finishing a complex task with more than 3 items and containing no verification step, it prompts to generate a verification nudge

This part of the source code is crucial:

if (
  allDone &&
  todos.length >= 3 &&
  !todos.some(t => /verif/i.test(t.content))
) {
  verificationNudgeNeeded = true
}

This shows it doesn't just "write lists," but also pushes for more rigorous verification when wrapping up a task.

1. The user provides a medium-complexity task
2. The model first writes 3-5 todos
3. After completing each item, the state is updated
4. When closing the final item, if no verification is present, it's reminded to add one

TodoWriteTool > Lightweight in-session task tracking

TaskCreate/Update/List > Formal task system

The value of TodoWriteTool is:

Make the model's current plan explicit at minimum cost, and integrate process constraints like "clear the list when done, don't forget verification for complex tasks" into the session state.