Your agent signs. Countersign proves it.

Install on a repository and Countersign opens one pull request that adds its checks. From then on every push and pull request gets a verdict in plain words: unfinished work the agent left behind, and whether the claims declared for the repository (tests pass, build succeeds, endpoint answers) actually hold. Every run leaves a receipt kept outside the repository, where the agent that wrote the code cannot edit it.

Countersign never runs your code on its own servers and never judges with a model. Verification happens in your own GitHub Actions with the open-source Countersign engine; this App keeps the record and reports it.