analysis_claude_code/docs/en/s03-todo-write.md
2026-02-27 02:19:54 +08:00

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# s03: TodoWrite
`s01 > s02 > [ s03 ] s04 > s05 > s06 | s07 > s08 > s09 > s10 > s11 > s12`
> *"An agent without a plan drifts"* -- list the steps first, then execute.
## Problem
On multi-step tasks, the model loses track. It repeats work, skips steps, or wanders off. Long conversations make this worse -- the system prompt fades as tool results fill the context. A 10-step refactoring might complete steps 1-3, then the model starts improvising because it forgot steps 4-10.
## Solution
```
+--------+ +-------+ +---------+
| User | ---> | LLM | ---> | Tools |
| prompt | | | | + todo |
+--------+ +---+---+ +----+----+
^ |
| tool_result |
+----------------+
|
+-----------+-----------+
| TodoManager state |
| [ ] task A |
| [>] task B <- doing |
| [x] task C |
+-----------------------+
|
if rounds_since_todo >= 3:
inject <reminder> into tool_result
```
## How It Works
1. TodoManager stores items with statuses. Only one item can be `in_progress` at a time.
```python
class TodoManager:
def update(self, items: list) -> str:
validated, in_progress_count = [], 0
for item in items:
status = item.get("status", "pending")
if status == "in_progress":
in_progress_count += 1
validated.append({"id": item["id"], "text": item["text"],
"status": status})
if in_progress_count > 1:
raise ValueError("Only one task can be in_progress")
self.items = validated
return self.render()
```
2. The `todo` tool goes into the dispatch map like any other tool.
```python
TOOL_HANDLERS = {
# ...base tools...
"todo": lambda **kw: TODO.update(kw["items"]),
}
```
3. A nag reminder injects a nudge if the model goes 3+ rounds without calling `todo`.
```python
if rounds_since_todo >= 3 and messages:
last = messages[-1]
if last["role"] == "user" and isinstance(last.get("content"), list):
last["content"].insert(0, {
"type": "text",
"text": "<reminder>Update your todos.</reminder>",
})
```
The "one in_progress at a time" constraint forces sequential focus. The nag reminder creates accountability.
## What Changed From s02
| Component | Before (s02) | After (s03) |
|----------------|------------------|----------------------------|
| Tools | 4 | 5 (+todo) |
| Planning | None | TodoManager with statuses |
| Nag injection | None | `<reminder>` after 3 rounds|
| Agent loop | Simple dispatch | + rounds_since_todo counter|
## Try It
```sh
cd learn-claude-code
python agents/s03_todo_write.py
```
1. `Refactor the file hello.py: add type hints, docstrings, and a main guard`
2. `Create a Python package with __init__.py, utils.py, and tests/test_utils.py`
3. `Review all Python files and fix any style issues`