Composer Tutorial

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Composer is PHP's dependency manager. It lets you declare the packages your project needs, downloads them (along with anything they need), and generates a single file you can require once to autoload everything — no more manually downloading libraries or writing your own class-loading code.

Where this fits: The Slim Framework track already showed you composer require slim/slim without explaining Composer itself in depth — this track fills that gap. If you've used npm for JavaScript or Maven for Java, Composer is PHP's equivalent.

What Problem Does Composer Solve?

Without Composer	With Composer
Manually download library files and copy them into your project	One command: `composer require vendor/package`
Write your own `include`/`require` chains for every class	One `require 'vendor/autoload.php';` loads everything
No easy way to track exact versions used	`composer.lock` pins exact versions for every install
Manually resolve which library needs which other library	Composer resolves the whole dependency tree for you

A Quick Look Ahead

Example: A Minimal composer.json

{
    "require": {
        "monolog/monolog": "^3.0"
    }
}

Example: Using an Installed Package

<?php
require __DIR__ . '/vendor/autoload.php';

$log = new \Monolog\Logger('app');
$log->info('Composer installed this class for us!');

Note: These are real, correct commands and code — but running them here would modify this site's own project files, so we won't execute Composer commands live on this page. Try them in your own project's terminal as you follow along.

Why Learn Composer?

Reason	What it means for you
Industry standard	Virtually every modern PHP project — Laravel, Symfony, Slim — uses Composer
Huge ecosystem	Packagist.org hosts hundreds of thousands of ready-to-use PHP packages
Reproducible installs	`composer.lock` means your whole team runs the exact same versions
Free autoloading	No more writing manual `include` statements for every class

Next steps: Head to Installation to get Composer set up on your machine.

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