Slim Framework — PHP Micro-Framework for APIs and Small Apps

Introduction

Slim is a PHP micro-framework for building APIs and small web applications. It provides routing, middleware, and PSR-7 HTTP message handling without the overhead of a full-stack framework. Slim is a good fit when you need a lightweight foundation and want to pick your own ORM, template engine, and libraries.

What Slim Does

• Routes HTTP requests to callable handlers using a fast, tree-based router
• Supports PSR-7 request and response objects for standards-compliant HTTP handling
• Provides a middleware stack for cross-cutting concerns like authentication and CORS
• Includes dependency injection via a PSR-11 compatible container
• Handles content negotiation, error rendering, and response streaming out of the box

Architecture Overview

Slim is built around the PSR-7 HTTP message interface and PSR-15 middleware dispatcher. Incoming requests are wrapped in a ServerRequest object, passed through a middleware stack, matched to a route, and dispatched to a handler that returns a Response. The framework ships with a default error handler, a routing middleware, and body-parsing middleware, but every component is replaceable.

Self-Hosting & Configuration

• Require via Composer: composer require slim/slim slim/psr7
• Use the official skeleton project for a pre-configured directory structure
• Configure routes in routes.php or directly on the App instance
• Add middleware globally or per-route for authentication, logging, or rate limiting
• Deploy behind Nginx or Apache with standard PHP-FPM configuration

Key Features

• Minimal footprint with no mandatory dependencies beyond PSR interfaces
• PSR-7 and PSR-15 compliance for interoperability with the PHP ecosystem
• Flexible dependency injection supporting any PSR-11 container
• Built-in error handling with JSON and HTML error renderers
• Route grouping and named routes for clean URL generation

Comparison with Similar Tools

• Laravel — full-stack framework with ORM, auth, and queues built in; Slim is lighter and lets you choose your own components
• Symfony — enterprise-grade component library; Slim offers faster bootstrapping for microservices and APIs
• Lumen — Laravel's micro-framework, now deprecated in favor of full Laravel; Slim remains independently maintained
• Mezzio (formerly Expressive) — PSR-15 middleware framework by Laminas; Slim has a simpler API and larger community

FAQ

Q: When should I choose Slim over Laravel? A: Choose Slim for APIs and microservices where you want minimal overhead and full control over your dependencies. Use Laravel when you need an integrated full-stack solution.

Q: Does Slim support middleware? A: Yes. Slim uses PSR-15 compatible middleware. You can stack middleware globally or on individual routes and route groups.

Q: Can I use Slim with an ORM like Eloquent or Doctrine? A: Yes. Slim does not include an ORM, but you can add Eloquent, Doctrine, or any other PHP ORM via Composer.

Q: What PHP version does Slim require? A: Slim 4.x requires PHP 7.4 or later. PHP 8.x is fully supported.

Sources

• https://github.com/slimphp/Slim
• https://www.slimframework.com/