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Discover top open-source software, updated regularly with real-world adoption signals.
Automated Ruby code reviews that simplify code and ensure test safety
Mutant runs mutation testing during pull‑requests and CI, suggesting simplifications that keep all tests green while highlighting missing test coverage.
Mutant is a mutation‑testing driven code review assistant for Ruby projects. It analyses each change, generates mutations, and reports simplifications that preserve existing test outcomes, effectively surfacing over‑engineered code and uncovered requirements.
During pull‑request reviews or incremental CI runs, Mutant flags alive mutations as actionable items, offering developers concise suggestions to reduce code size without breaking tests. It integrates with popular test frameworks such as RSpec and Minitest, supports Linux and macOS, and runs on Ruby 3.2‑3.4 (cRUBY/MRI). The tool also produces semantic code‑coverage metrics that go beyond line‑level statistics, helping teams identify missing tests for implicit requirements.
Open‑source projects can use Mutant for free by declaring --usage opensource. Commercial teams require a subscription per developer, with monthly or annual plans available in USD and EUR. Configuration is performed via CLI flags or a config file, and the tool can be added to CI pipelines in incremental mode to prevent merging code with new alive mutations.
When teams consider Mutant, these hosted platforms usually appear on the same shortlist.
Looking for a hosted option? These are the services engineering teams benchmark against before choosing open source.
Pull‑request review
Automatically suggests code simplifications that keep tests passing, reducing technical debt before merge.
CI regression guard
Fails builds when new alive mutations appear, ensuring every change is fully covered by tests.
Test suite audit
Identifies uncovered requirements, prompting addition of missing tests to improve semantic coverage.
Legacy code cleanup
Reveals dead or over‑specified code sections, guiding safe refactoring of older modules.
Mutant treats each uncovered mutation as a code‑review action, providing concrete simplification suggestions rather than just a coverage score.
Supported runtimes include cRUBY/MRI 3.2, 3.3, and 3.4 with full syntax and mutation analysis.
Yes, open‑source usage is free when the repository is public and the `--usage opensource` flag is set.
Add Mutant in incremental mode to the CI script; the build will fail if alive mutations remain after the run.
Commercial projects need a paid subscription per developer, with monthly or annual plans available in USD and EUR.
Project at a glance
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