# Stryker

Mutation testing for JavaScript and friends

Repository: https://github.com/stryker-mutator/stryker-js
Canonical: https://ross.abutalabs.com/products/stryker
Homepage: https://stryker-mutator.io
Language: TypeScript
License: Apache-2.0
License Family: permissive
Topics: mutation-testing, stryker, javascript, typescript, testing-tools, test-automation, testing, hacktoberfest
Last push: 2026-08-26T19:21:23+00:00
Link (homepage): https://stryker-mutator.io
Link (site_page): https://stryker-mutator.io/docs/stryker-js/introduction
Link (site_page): https://stryker-mutator.io/docs/stryker-net/introduction
Link (site_page): https://stryker-mutator.io/docs/stryker4s/getting-started
Link (site_page): https://stryker-mutator.io/docs/General/example

## Health v2 (maintenance only)
Score: 95/100 (v2, computed 2026-09-03T02:20:16.233290+00:00)
- activity 99, release rhythm 86, longevity 100
- inputs: {"age_days": 3855, "days_push": 7, "days_rel": 19, "gap_med": 34, "n_releases_24m": 14}
- flags: none
- formula: round(0.45*activity + 0.35*rhythm + 0.20*longevity); archived -> min(score, 10)

## Adoption (not part of the score)
Stars 3050, forks 278 (observed 2026-08-28T04:07:39.595442+00:00)

## What it is
Stryker is a mutation testing tool family that measures the effectiveness of your unit tests by automatically inserting bugs (mutants) into your source code and checking whether your tests catch them. It supports JavaScript/TypeScript (StrykerJS), .NET (Stryker.NET), and Scala (Stryker4s), with test-runner-agnostic execution and detailed HTML mutation reports.

## Use cases
- measure how effective my unit tests really are
- find gaps in test coverage beyond code coverage metrics
- run mutation testing on a TypeScript project
- run mutation testing on a .NET Core project
- generate a mutation score report in CI
- find tests with missing assertions
- improve test quality for a JavaScript codebase

## When to choose
- you want to evaluate test quality beyond line coverage
- you work in JavaScript, TypeScript, C#, or Scala and want a mature, actively maintained mutation testing tool
- you need test-runner-agnostic mutation testing with HTML reports
- you want to catch surviving mutants that indicate weak or missing assertions

## When to avoid
- your test suite is slow, since mutation testing runs tests many times and can be very time-consuming
- you need mutation testing for languages other than JavaScript/TypeScript, C#, or Scala
- you only need simple code coverage metrics rather than test effectiveness analysis

## Facets
- artifact type: cli-tool
- maturity: active
- function: testing, cli, developer-tools
- domain: testing, developer-tools, web-development
- platform: cross-platform, cli, dotnet
- tags: mutation-testing, test-quality, typescript, javascript, csharp, scala, test-runner-agnostic, nodejs

## Member repositories
- stryker-mutator/stryker-js (main) score 95
- stryker-mutator/stryker-net (sdk) score 92

## Provenance
- Observed fields: from GitHub, fetched 2026-08-28T04:07:39.595442+00:00.
- Health v2: computed from the inputs above; adoption is never an input.
- Inferred fields (summary, facets, guidance): AI-extracted, prompt v1, taxonomy v1, on 2026-08-29T18:46:49.833801+00:00, confidence not recorded.
  - readme: https://github.com/stryker-mutator/stryker-js (fetched 2026-08-28T04:07:39.595442+00:00, sha 18169346aeba)
  - homepage: https://stryker-mutator.io (fetched 2026-08-29T09:44:32.432149+00:00, sha d23188ee5838)
  - site_page: https://stryker-mutator.io/docs/stryker-js/introduction (fetched 2026-08-29T09:44:32.441047+00:00, sha 59fad0909734)
  - site_page: https://stryker-mutator.io/docs/stryker-net/introduction (fetched 2026-08-29T09:44:32.442797+00:00, sha 455f8dd67833)
  - site_page: https://stryker-mutator.io/docs/stryker4s/getting-started (fetched 2026-08-29T09:44:32.444504+00:00, sha 5641cba1d5e6)
  - site_page: https://stryker-mutator.io/docs/General/example (fetched 2026-08-29T09:44:32.446446+00:00, sha 72a3dea5489f)
  - site_page: https://stryker-mutator.io/docs (fetched 2026-08-29T09:44:32.448442+00:00, sha 8705d3f8dae2)
  - site_page: https://stryker-mutator.io/docs/mutation-testing-elements/supported-mutators (fetched 2026-08-29T09:44:32.450182+00:00, sha b8d500101e28)
  - site_page: https://stryker-mutator.io/docs/General/faq (fetched 2026-08-29T09:44:32.452032+00:00, sha f310efb43737)
- Data as of 2026-08-30T08:39:29.467469+00:00.