# Stryker mutation testing

> Tests for your tests. It mutates the code and checks your suite notices.

- Verdict: My default
- Vendor: Open source
- Layer: [Build and test](https://cloudlesslabs.com/stack/layers/dev.md). Job: Test quality
- Last reviewed: 18 October 2026, by Nicolas Dao (Cloudless Labs, Sydney)
- Web page: https://cloudlesslabs.com/stack/stryker/. The whole stack in one file: https://cloudlesslabs.com/stack/brief.md

When agents write most of the code and the tests, mutation testing is how I know the tests are worth anything.

## Use it when

- Agent-written code: it proves the tests actually catch bugs.

## Pricing

Free.

## Where it fits

- [Building with AI agents](https://cloudlesslabs.com/stack/use-cases/ai-dev.md): pick 4. Proves the tests catch bugs.

## Sources

- [Stryker](https://stryker-mutator.io/)

## Related

- [Build and test](https://cloudlesslabs.com/stack/layers/dev.md): every tool in this layer, with its verdict
- [The whole stack in one file](https://cloudlesslabs.com/stack/brief.md): every use case and tool, for questions that span many
- [Map of every Markdown file on cloudlesslabs.com, with what each one answers](https://ask.cloudlesslabs.com)