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Head-to-head · Mutation Testing Tools

Infection vs Cosmic Ray

  • Updated Sep 2026
  • Both researched from official sources
  • 5 checks side by side
Higher score Infection #4 in Mutation Testing Tools 7.4/10 Free plan Free plan✓ 4 of 4 features Visit Infection
Cosmic Ray #5 in Mutation Testing Tools 7.1/10 Free plan Free plan✓ 3 of 4 features Visit Cosmic Ray

Infection leads on 1 check, Cosmic Ray on 0, and 4 are even. Who comes out ahead on the 5 yes/no, price and count checks where we have data for both products. The editor score weighs everything else too.

Our verdict

  • Highest scoreInfection · 7.4/10
  • Free planboth
  • Most featuresInfection · 4 of 4

Infection scores higher on our rubric for mutation testing tools: 7.4 against 7.1 out of 10; our editors rank them #4 and #5.

Infection offers mutation quality gate; Cosmic Ray doesn't publish it.

Infection is the better fit for PHP teams with CI quality gates. Cosmic Ray is the better fit for python teams needing distributed mutation runs.

  • Infection fits best

    PHP teams with CI quality gates

  • Cosmic Ray fits best

    Python teams needing distributed mutation runs

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Side by side

Feature Infection 7.4/10 Visit ↗ Cosmic Ray 7.1/10 Visit ↗
At a glance
Editor score 7.4 7.1
Ranking #4 in Mutation Testing Tools #5 in Mutation Testing Tools
Best for PHP teams with CI quality gates Python teams needing distributed mutation runs
Pricing model Free Free
Starting price Not published Not published
Free plan ✓ ✓
Free trial — —
Deployment Self-hosted Self-hosted
Support Community, Docs Docs
Built for Solo, Small business, Mid-market, Enterprise Solo, Small business, Mid-market
Features Infection 4/4 · Cosmic Ray 3/4
Incremental analysis ✓ ✓
Parallel execution ✓ ✓
Surviving mutant reports ✓ ✓
Mutation quality gate ✓ (best) Not published
Specs
Supported languages PHP Python 3
Test frameworks PHPUnit, PhpSpec, Codeception, Testo unittest, pytest, nose
Mutation operators Arithmetic, boolean, cast, conditional boundary, conditional negotiation, equality, function signature, nullify, number, operator, regex, removal, return value, visibility, and unwrap mutators binary operator replacement; boolean replacement; break/continue replacement; comparison operator replacement; exception replacement; keyword replacement; number replacement; decorator removal; unary operator replacement; zero-iteration for loops
Our review
Pros
  • Broad PHP mutators with configurable profiles and custom mutators
  • Parallel execution, coverage reuse, and changed-line filtering
  • CI thresholds with HTML, text, JSON, GitHub, and GitLab reports
  • Supports configurable mutation operators and user-supplied test commands
  • Resumable sessions help preserve mutation run results
  • Distributed HTTP workers enable concurrent mutation execution
Cons
  • Supports PHP rather than multiple programming languages
  • No AI features are included
  • Mutation analysis is centered on supported PHP test frameworks
  • Supports Python 3 rather than multiple programming languages
  • No listed external integrations or quality gate
  • Requires teams to work with mutation testing reports directly
Our verdict

Infection is an open-source mutation testing framework for PHP teams that want to measure whether their tests detect code changes. It uses AST-based source-code mutation, runs relevant test cases, and reports killed, escaped, errored, and…

Read the review →

Cosmic Ray is an open-source mutation testing tool for Python 3, intended for developers and teams assessing how effectively their test suites detect code changes. It modifies source code with configurable mutation operators, runs a…

Read the review →
  1. InfectionMutation Testing Tools 7.4Free plan
  2. Cosmic RayMutation Testing Tools 7.1Free plan

Strengths and trade-offs

  • Infection — where it wins

    • Broad PHP mutators with configurable profiles and custom mutators
    • Parallel execution, coverage reuse, and changed-line filtering
    • CI thresholds with HTML, text, JSON, GitHub, and GitLab reports

    Where it doesn't

    • Supports PHP rather than multiple programming languages
    • No AI features are included
    • Mutation analysis is centered on supported PHP test frameworks

  • Cosmic Ray — where it wins

    • Supports configurable mutation operators and user-supplied test commands
    • Resumable sessions help preserve mutation run results
    • Distributed HTTP workers enable concurrent mutation execution

    Where it doesn't

    • Supports Python 3 rather than multiple programming languages
    • No listed external integrations or quality gate
    • Requires teams to work with mutation testing reports directly

More comparisons

All mutation testing tools comparisons → · Full ranking →

Reviewed by iTechGuides Editors · Editorial team · Updated Sep 2026

Last updated · How we research and update