infection
Infection is a PHP mutation testing framework that verifies code test quality by intentionally introducing bugs (mutations) into your code and checking if tests catch them. It helps teams identify weak test coverage and improve overall test effectiveness.
Key facts
Objective fields from the source. Values we can't verify are shown as “Unknown” rather than guessed.
| Field | Value |
|---|---|
| Repository | infection/infection |
| Owner | infection |
| Primary language | PHP |
| License | BSD-3-Clause — OSI-approved |
| Stars | 2.2k |
| Forks | 185 |
| Open issues | 209 |
| Latest release | 0.34.0 (2026-06-28) |
| Last updated | 2026-07-08 |
| Source | https://github.com/infection/infection |
What infection is
Infection performs mutation analysis on PHP codebases by modifying AST nodes and re-running test suites to measure test resilience. It generates mutation scores (MSI) to quantify test quality and integrates with CI/CD pipelines via CLI and configuration files.
Get the infection source
Clone the repository and explore it locally.
git clone https://github.com/infection/infection.gitcd infection# follow the project's README for install & configurationNeed it deployed, integrated, or customized instead? DEV.co ships production installs.
Best use cases
Implementation considerations
- Requires PHP 8.3.0+ and Composer integration; install via Composer as a dev dependency.
- Plan for significant build time; mutation analysis re-runs full test suites multiple times. Consider sample-based mutation or parallelization for large projects.
- Configure mutation score thresholds in infection.json to enforce quality gates in CI pipelines.
- Test suite must be reliable and fast; flaky tests will generate false positives and slow down analysis.
- Baseline mutation scores typically start 40-60% MSI for average codebases; plan realistic improvement targets.
When to avoid it — and what to weigh
- Non-PHP Projects — Infection is PHP-specific. Alternative mutation testing tools exist for Python, Java, JavaScript, and other languages; this will not work outside PHP ecosystems.
- Projects with Very Large Test Suites — Mutation testing re-runs your entire test suite for each mutation. Large suites can result in significant runtime overhead; consider test parallelization or sampling strategies.
- Real-time Feedback Requirements — Mutation analysis is computationally expensive and not suitable for tight development loops. Best run as scheduled CI jobs or pre-commit hooks on focused changesets.
- PHP < 8.3.0 Environments — Requires PHP 8.3.0 or higher; older projects will need environment upgrades or cannot use this tool.
License & commercial use
BSD-3-Clause license (permissive, OSI-approved). Permits commercial use, modification, and distribution with conditions: retain license notice and disclaimer of liability.
BSD-3-Clause is a permissive license allowing commercial use. No proprietary restrictions; safe for commercial deployment. However, ensure your organization's legal team reviews the liability disclaimer clause, particularly if Infection becomes part of a critical quality-gate process.
DEV.co evaluation signals
Editorial assessment — not user reviews. Directional, with an explicit confidence level.
| Signal | Assessment |
|---|---|
| Maintenance | Active |
| Documentation | Strong |
| License clarity | Clear |
| Deployment complexity | Low |
| DEV.co fit | Good |
| Assessment confidence | High |
Infection executes mutated code within test contexts; ensure test isolation is robust to prevent side effects from mutations. No embedded cryptographic or network functionality noted. As a dev-only tool, security posture depends on your test suite's integrity. No security audit data provided; consider internal review if used in highly regulated environments. Standard PHP execution risks apply.
Alternatives to consider
Humbug
Predecessor to Infection; discontinued. Infection is the recommended successor with active maintenance and improved PHP 8 support.
Stryker (JavaScript/TypeScript, C#, Java)
Multi-language mutation testing framework with similar architecture. Use if your codebase spans non-PHP languages.
PIT (Java) or Mutant (Python)
Language-specific mutation testing tools. Necessary if migrating away from PHP or supporting polyglot codebases.
Build on infection with DEV.co software developers
Start with Infection's browser playground or integrate into your CI/CD pipeline. Request help from our team to set up mutation testing thresholds and reduce false regressions.
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infection FAQ
Does Infection replace code coverage tools?
How long does a mutation analysis run take?
Can I use Infection in my local development workflow?
What PHP versions are supported?
Custom software development services
DEV.co helps companies turn open-source tools like infection into production software. Our software development services cover the full lifecycle — architecture, web development, integration, and maintenance — delivered by software developers and web developers who ship. Engage our software development agency to implement or customize it for your open-source testing stack.
Ready to Validate Your PHP Test Quality?
Start with Infection's browser playground or integrate into your CI/CD pipeline. Request help from our team to set up mutation testing thresholds and reduce false regressions.