What is Composer in PHP?

Composer is PHP's standard dependency manager. It allows you to declare the libraries your project depends on and manages installing and updating them. Create a composer.json file specifying dependencies: { "require": { "vendor/package": "^2.0" } }. Run composer install to download dependencies to the vendor/ folder. Composer also provides autoloading — just include vendor/autoload.php and all installed packages and your own classes (configured in the autoload section) are available without manual require statements. It uses the composer.lock file to lock dependency versions for reproducible builds. Packagist (packagist.org) is the main repository for Composer packages.