PHP-FIG

PHP-FIG is a group that publishes interoperability recommendations and PHP Standards Recommendations, commonly called PSRs. These standards let packages cooperate without sharing one framework.

Why Interoperability Matters

An application often needs a logger, cache, HTTP client, or dependency-injection container. Without shared contracts, each library would accept a different kind of object. A PSR gives package authors a common interface to work against.

PHP-FIG does not publish a framework and it does not require an application to adopt every PSR. Projects use the recommendations that solve a real integration problem. A Laravel, Symfony, or framework-free application may all depend on selected PSRs.

Interfaces And Implementations

A standards package usually defines interfaces rather than doing the work itself. For example, psr/log provides Psr\Log\LoggerInterface. An application still needs an implementation such as Monolog or a framework logger.

This distinction matters when reading documentation. The PSR tells you which methods consumers may rely on. The implementation documentation tells you how to configure handlers, storage, retries, or other runtime behaviour.

<?php

declare(strict_types=1);

use Psr\Log\LoggerInterface;

final class PaymentReporter
{
    public function __construct(private LoggerInterface $logger)
    {
    }

    public function reportFailure(string $paymentId): void
    {
        $this->logger->warning('Payment failed', [
            'payment_id' => $paymentId,
        ]);
    }
}

PaymentReporter does not need to know which logger receives the message. The application bootstrap or service container chooses that implementation.

Using PSRs Sensibly

Look for standards at boundaries where packages meet: logs, HTTP messages, cache access, clocks, and containers. Do not add an interface merely to make a small local helper look more abstract. Existing project conventions still matter, and replacing a well-understood local abstraction may create work without improving the application.