# Checkpoints

> Checkpoints on code.extension.dev record the files after every applied edit, and a rewind takes the terminal conversation back with them.

Canonical: https://docs.extension.dev/code/checkpoints
This page as Markdown: https://docs.extension.dev/code/checkpoints.md
Section: Code
Siblings: [AI generation](https://docs.extension.dev/code.md) · [Terminal](https://docs.extension.dev/code/terminal.md) · [Chat mode](https://docs.extension.dev/code/chat-mode.md) · [Starters and templates](https://docs.extension.dev/code/starters.md) · [Live preview](https://docs.extension.dev/code/preview.md) · [Select to edit](https://docs.extension.dev/code/select-to-edit.md) · [The Code tab](https://docs.extension.dev/code/code-tab.md) · [Build console](https://docs.extension.dev/code/build-console.md) · [Drafts](https://docs.extension.dev/code/drafts.md) · [Firefox engine](https://docs.extension.dev/code/firefox-engine.md) · [Download and run locally](https://docs.extension.dev/code/download-and-run.md) · [Share links](https://docs.extension.dev/code/share.md) · [Publish and import](https://docs.extension.dev/code/publish.md) · [Generation allowance](https://docs.extension.dev/code/allowance.md) · [Settings and sign-in](https://docs.extension.dev/code/settings.md)
Map of every page: https://docs.extension.dev/llms.txt · Whole corpus: https://docs.extension.dev/llms-full.txt

---

# Checkpoints

A checkpoint is a snapshot of the project's files, written every time an
edit is applied. Reach for one when a change went wrong and you want the
files, or the files and the conversation, back where they were.

## Quick start

Open the control in the header that shows your extension's name. The list
holds every checkpoint under the prompt that made it. Press **Restore last
known good** to go back to the newest checkpoint whose build passed, or pick
any row to restore it.


## How it works

### What writes a checkpoint

Each applied edit writes one: an agent turn's writes, a chat answer's
operations, and a **Save & rebuild** in the Code tab. Seeding a template
writes one too, and so does a restore, which first saves the files you are
leaving as `Before restoring: <label>`. The `checkpoint <message>` command
records one under your own message. A project keeps its 50 newest.

### The build's verdict

A checkpoint is stamped with the build's own conclusion once the compile
finishes: success or failed, with the error count. **Restore last known
good** picks the newest checkpoint whose build succeeded, excluding the one
you are on. A checkpoint with no verdict is one whose files were never built.

### Rewind the conversation too

A checkpoint written by a terminal turn carries a chip with the turn that
produced it. On the first checkpoint of each turn the row offers **Resume fx
here**. Take it and two things happen together: the files go back to that
checkpoint, and the conversation goes back to that turn. The confirmation
names the turn and counts the turns you are about to leave behind.

The turns you leave are parked as a branch. The branch appears in the same
list as a row reading `Branch from turn 2, 3 later turns` with **Resume this
branch**. Resuming a branch is a swap: the live conversation becomes a
branch, the branch becomes live, and the files go back to the last
checkpoint that branch recorded.

Three branches are kept per project. When a fourth would be created the
oldest is dropped, and the confirmation says so before you press the button.

After a rewind the agent does not remember the turns past the checkpoint
and is told not to cite them. It still reads the files in front of it. If
you want it to know something from a parked branch, say it again.

### Where checkpoints live

Checkpoints are stored in the browser that made them, not with the draft on
your account. Every checkpoint has an address, `/drafts/<id>/c/<n>`, that
shows its message, when it was saved, and its file list, with **Restore this
checkpoint** and **Open project**. Open that address on another device and
it says the checkpoint is not there.

## Reference

| Control | What it does |
| --- | --- |
| **Restore last known good** | Restores the newest checkpoint whose build succeeded |
| A checkpoint row | Restores those files |
| **Resume fx here** | Restores the files and rewinds the conversation to that turn |
| **Resume this branch** | Swaps the live conversation with a parked branch |
| `checkpoint <message>` | Records a checkpoint under your message |

| Limit | Value |
| --- | --- |
| Checkpoints kept per project | 50 |
| Parked branches per project | 3 |
| Address of the nth checkpoint | `/drafts/<id>/c/<n>` |

## When it fails

- **A row reads `Older than fx remembers`.** The conversation has compacted
  past that turn, so there is nothing to resume from. The files still
  restore. Pick a later row to rewind the conversation.
- **Restore last known good is missing.** No checkpoint other than the
  current one has a passing verdict. Pick a row by its message instead.
- **The checkpoint address says it is not on this device.** Checkpoints live
  in the browser that made them. Open the draft in that browser, or restore
  from the draft on your account and build again.
- **The agent cites a turn you rewound past.** It should not, and the files
  are the shared memory. Say the fact again in the next prompt.

## Next

- [Terminal](/code/terminal) for the turns a checkpoint is tied to
- [Drafts](/code/drafts) for what syncs to your account and what stays here
- [The Code tab](/code/code-tab) for the save that writes a checkpoint