PSR Standards in PHP: A Practical Guide for Developers

Are you tired of wrestling with inconsistent PHP codebases or struggling to make different packages work together? You're not alone! In this series, you'll explore how PHP-FIG's PSR standards can transform your development experience.

What is PHP-FIG?

PHP-FIG is a group of PHP project representatives working together to advance the PHP ecosystem. Their primary contribution is the PSR system, which defines coding standards and interfaces that enable better interoperability between PHP packages and frameworks.

Why PSRs Matter

PSRs solve several critical challenges in PHP development:

• Code Consistency: Standardized coding styles make code more readable
• Interoperability: Common interfaces allow different packages to work together seamlessly
• Best Practices: Established patterns improve code quality and maintainability

Recommended Reading Path

New to PSRs? Follow this order — it builds knowledge progressively:

Foundation (Start Here)

1. PSR-1: Basic Coding Standard — The "house rules" for PHP code
2. PSR-12: Extended Coding Style — Detailed formatting rules (extends PSR-1)
3. PSR-4: Autoloading Standard — How PHP finds your classes automatically

Core Infrastructure

1. PSR-3: Logger Interface — Standardized logging across your application
2. PSR-11: Container Interface — Dependency injection made interoperable
3. PSR-14: Event Dispatcher — Decoupled communication between components

HTTP Stack (Read in Sequence)

1. PSR-7: HTTP Message Interfaces — The standard "shape" of HTTP requests and responses
2. PSR-17: HTTP Factories — Creating PSR-7 objects without coupling to implementations
3. PSR-15: HTTP Handlers and Middleware — Processing HTTP requests through a middleware pipeline
4. PSR-18: HTTP Client — Sending HTTP requests the standard way

Data and Caching

1. PSR-6: Caching Interface — Full-featured cache pools and items
2. PSR-16: Simple Cache — Lightweight key-value caching

Specialized

1. PSR-13: Hypermedia Links — Self-documenting REST APIs with HATEOAS
2. PSR-20: Clock Interface — Testable time handling

Quick Reference (by PSR Number)

PSR	Topic	Post
1	Basic Coding Standard	Read
3	Logger Interface	Read
4	Autoloading Standard	Read
6	Caching Interface	Read
7	HTTP Messages	Read
11	Container Interface	Read
12	Extended Coding Style	Read
13	Hypermedia Links	Read
14	Event Dispatcher	Read
15	HTTP Handlers	Read
16	Simple Cache	Read
17	HTTP Factories	Read
18	HTTP Client	Read
20	Clock	Read

Practical Learning

Each post includes:

• A relatable analogy explaining what the standard solves
• The actual PSR interface with commentary
• A working implementation from the blog API companion project
• Common mistakes with before/after fixes
• Framework integration examples (Laravel, Symfony, Slim)
• A "Try It Yourself" section with exact commands to run

Getting Started

To follow along, clone the companion repository — a blog API that uses all 14 PSRs:

git clone https://github.com/jonesrussell/php-fig-guide.git
cd php-fig-guide
composer install

The blog API demonstrates every PSR in a real project context. Each PSR has:

• Implementation code under src/
• PHPUnit tests under tests/

# Run all tests
composer test

# Run tests for a specific PSR
composer test -- --filter=PSR7

# Check coding standards (PSR-1 + PSR-12)
composer check-style

Resources

• PHP-FIG Website
• PSR Index
• Our Example Repository

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