Checkpoints: Undo Any Change the Agent Makes
After every successful turn, Mythex saves a checkpoint of your project. Revert to any of them in two clicks, or edit an earlier message and try again.
Mythex Team · · 4 min read
Every time the Mythex agent finishes a turn successfully, it saves a checkpoint of your project's files. If a later change goes wrong, you can roll the project back to any of those points from the chat — no need to describe the damage and hope the agent can repair it. You can also edit an earlier message and resend it, which rewinds the project and tries a different prompt from there.
What a checkpoint is
A checkpoint is a saved snapshot of your project files at the end of a turn. Under the hood it is a git checkpoint — git being the version-control system developers use to track every change to a codebase. You don't need to know git to use it; the chat handles it for you.
Checkpoints are saved after a successful agent turn. Each one sits at the end of the agent's reply that produced it, so the chat history doubles as a timeline of your project: every reply marks a point you can return to.
Why it helps
Building with an agent is iterative. Most turns move the project forward, but some don't — a layout change that breaks the phone view, a refactor that goes further than you wanted, a feature that turns out to be the wrong idea.
When that happens, the tempting move is to ask the agent to fix it. Sometimes that works. Often it layers a new change on top of a bad one, and then another, and each fix makes the next harder. Rolling back to the last good point is usually faster and cheaper than fighting compounding errors. You start again from something that worked.
It also makes it safer to try things. If you can undo a turn in two clicks, asking "what if the hero section was a video?" costs you very little.
How to revert to a checkpoint
- Find the reply that left the project in the state you want to go back to.
- Click Revert to this point — the undo icon at the end of the reply, next to Copy. On a laptop, the icon appears when you hover over the reply.
- Confirm with Restore in the dialog that asks.
Your project files roll back to how they were at the end of that turn. Check the preview to confirm, then carry on from there.
Edit and resend
Sometimes the problem wasn't the result, it was the prompt. For that, there's Edit and resend:
- Hover over one of your earlier messages and click to edit it.
- Rewrite the prompt the way you should have phrased it.
- Confirm Discard & resend.
Mythex rewinds the project to before that turn — when a checkpoint exists — and sends your new prompt. It's the fastest way to retry a turn that went in the wrong direction without leaving the bad attempt's changes in place.
Checkpoints work best with small steps
A checkpoint can only take you back to the end of a turn. If one turn did five things, you can undo all five or none. That's one more reason to keep each request small:
- Change one section.
- Fix one bug.
- Add one page.
Smaller asks mean fewer surprises and lower credit use, and each one leaves a checkpoint you can return to on its own.
It also helps to describe what you see in the preview rather than what you think the code should do — for example, "On the pricing page, the Pro card's button is cut off on mobile. Fix the overflow and keep the desktop layout."
For large features, start in Plan mode: the agent sets out an approach, you approve it, then Build works through it. More on that in Plan before you build.
When to revert, and when to rebuild
Reverting is the right move when the project was in a good state a few turns ago. A full rebuild is only worth it when:
- You've changed the product idea completely.
- The architecture is wrong for the new requirements.
- The project is still empty or nearly empty.
Even then, say what to keep — the name, brand colours, content — so you don't lose what was already right.
Limits
- Checkpoints are saved after successful turns, and Discard & resend can only rewind when a checkpoint exists.
- Reverting rolls back your project files to how they were at that point.
- A checkpoint covers a whole turn. You can't undo part of one; smaller turns give you finer control.
- On a laptop the Revert icon only shows on hover, so move the pointer over the reply if you can't see it.
If you're working through a bug rather than undoing one, our guide to debugging an AI-built app covers the other half of the process.
The docs cover checkpoints in Chat and in Iterate without rebuilding.