How does this skill improve my PHP unit tests?

By identifying non-deterministic code (like calling 'new DateTime()' inside a method), it helps you refactor to inject dependencies, allowing you to mock values and eliminate flaky test results.

What is a pure function in PHP?

A pure function is a method that always returns the same output for the same input and has no side effects (like writing to a database or changing global state), making it extremely easy to test.

Can it detect side effects like database writes or file I/O?

Yes, it specifically flags I/O operations and state mutations that occur within calculation logic, suggesting a separation between pure domain logic and impure infrastructure calls.

Does this support modern PHP patterns like Immortality and Readonly classes?

Absolutely. The skill encourages the use of immutable objects and with-style setters to ensure methods return new instances rather than modifying existing input parameters.

PHP Pure Function Checker

Name: PHP Pure Function Checker
Author: dykyi-roman

bydykyi-roman

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Security & Testing

Analyzes PHP codebases to identify and refactor impure functions into deterministic, side-effect-free, and highly testable code.

The PHP Pure Function Checker is a specialized skill for Claude Code designed to enhance software architecture by promoting functional programming principles within PHP applications. It systematically scans source code for non-deterministic patterns—such as hardcoded timestamps, random number generation, and global state dependencies—and provides actionable refactoring suggestions. By transforming impure logic into pure functions, developers can significantly improve unit test reliability, reduce unintended side effects, and create more predictable domain logic within DDD, Hexagonal, and Clean Architecture projects.

Key Features

0145 GitHub stars

02Provides automated Grep patterns for rapid scanning across large PHP repositories.

03Analyzes dependencies on mutable instance state and global or static variables.

04Detects non-deterministic methods like hardcoded dates and random values.

05Identifies hidden side effects such as I/O operations inside business logic.

06Flags methods that modify input parameters instead of returning new states.

Use Cases

01Refactoring legacy PHP code to improve unit test coverage and eliminate flaky tests.

02Enforcing 'Functional Core, Imperative Shell' patterns in Clean Architecture projects.

03Automating code reviews to ensure domain services remain side-effect-free and predictable.

What are Skills?·How to Install

Install with 🐟 Skill.Fish

npx skillfish add dykyi-roman/awesome-claude-code check-pure-functions

For use in Claude.ai and ChatGPT

Download Skill