henitai

https://github.com/martinotten/henitai

Hen'i-tai (変異体) is a mutation testing framework for Ruby 3.3.6+. It produces Stryker-compatible mutation-testing-report-schema JSON, integrates with the Stryker Dashboard, and ships with a standalone HTML report powered by mutation-testing-elements. A free, open-source alternative to the mutant gem — with built-in cost-reduction strategies, per-test coverage analysis, and CI/CD integration out of the box.