What is composer?

Composer is a tool for PHP that helps you manage the external libraries (called “packages”) your project needs. It automatically downloads the right versions, keeps them organized, and makes them easy to use in your code.

Let's break it down

  • composer.json - a file where you list the packages you want and any version constraints.
  • composer.lock - records the exact versions that were installed, so everyone on the team gets the same set.
  • vendor folder - where Composer puts the downloaded packages.
  • autoload.php - a generated file that lets you load any class from those packages without manual includes.
  • Common commands: composer install, composer update, composer require, composer dump-autoload.

Why does it matter?

Without Composer, you’d have to find, download, and update each library by hand, which is time‑consuming and error‑prone. Composer ensures you always have the correct, compatible versions, makes updates simple, and provides automatic class loading, so you can focus on writing your own code.

Where is it used?

Composer is used in virtually every modern PHP project: web applications, APIs, and frameworks such as Laravel, Symfony, Drupal, and Magento. Even many WordPress plugins rely on Composer to manage their dependencies.

Good things about it

  • Handles complex dependency trees automatically.
  • Guarantees consistent environments with the lock file.
  • Large public repository (Packagist) with thousands of ready‑to‑use packages.
  • Generates an autoloader, removing the need for manual require statements.
  • Simple command‑line interface that works on any OS with PHP installed.

Not-so-good things

  • Requires a learning curve for beginners unfamiliar with the command line or JSON files.
  • Relies on an internet connection to fetch packages, which can be a problem in offline environments.
  • Version conflicts can arise when two packages need different versions of the same library.
  • The vendor directory can become large, adding weight to the project if not managed properly.