Coming from Stryker

oxmutate is built to replace stryker run in a project that tests with Vitest, without touching the project. The config stays, the report format stays, the disable comments stay. The command changes.

The switchCopy Anchor Link

- npx stryker run
+ npx oxmutate run

  "scripts": {
-   "test:mutation": "stryker run"
+   "test:mutation": "oxmutate run"
  },
  "devDependencies": {
-   "@stryker-mutator/core": "^10.0.0",
-   "@stryker-mutator/vitest-runner": "^10.0.0",
+   "oxmutate": "^0.1.0",
    "vitest": "^4.1.0"
  }

Both write reports/mutation/mutation.json by default. To run them side by side and compare, give oxmutate a directory of its own: npx oxmutate run --report-dir reports/oxmutate.

What carries over unchangedCopy Anchor Link

• stryker.config.{mjs,js,cjs,json}, read as it stands. Every key oxmutate uses is on Configuration, and every key it does not use is listed in the run's output with the reason.
• The JSON report (schema 2), so mutation-testing-elements, the HTML report and any tool that reads Stryker's report read oxmutate's.
• The mutant set: Stryker 10.0.0's 17 mutator families. The Regex family gives the same mutants as weapon-regex on 928 of 932 real patterns.
• // Stryker disable next-line <Mutator>: <reason> comments, honoured as written.
• thresholds, including break, and mutator.excludedMutations.

What differs, on purposeCopy Anchor Link

• Code inside TypeScript as casts and enums is mutated. Stryker 10.0.0 skips it. --stryker-compat (or strykerCompat: true) gives Stryker's mutant set exactly.
• The default per-mutant slack is 500 ms, not 5,000 ms. A warm in-process run has no process start-up to absorb. Set timeoutMS to keep Stryker's.
• Static mutants are scored, not skipped. Each is re-run with the mutant armed from process start, in its own Vitest start, scoped to the test files that load it. ignoreStatic: true skips them, as Stryker does.
• Plugins are data. There are no runtime plugins: an ignorer plugin becomes an ignore rule, { call: 'console.*', reason: '…' }.
• The checker reads the original sources. checkers: ['typescript'] compiles each survivor with the project's own compiler; instrumented files carry // @ts-nocheck and are never type-checked.

What is not there yetCopy Anchor Link

The Stryker Dashboard reporter, eventReporter, logLevel and fileLogLevel. A config that sets them runs, and lists each as unused.

How closely the verdicts agreeCopy Anchor Link

No Stryker suite is graded through compat-oracle, so in this family's sense the switch is not graded: compat-oracle grades an import by the incumbent's own test suite, and a mutation tester produces a verdict per mutant rather than a passing test. What is measured instead is verdict agreement: the same project scored by Stryker 10.0.0 and by oxmutate, each mutant's verdict compared against Stryker's own JSON report. Measured on 2026-10-27:

On paratext one mutant disagreed: Stryker called it a timeout, and its covering tests pass with it, because Stryker's hit limit stopped a loop that ends. On controlroom Stryker's worker errored on one mutant, so there is no Stryker verdict to compare it with; it has not been checked by hand yet. The method, the subjects and the speed measured on the same runs are in m1-results.md.