Composer
Composer is a dependency management tool for PHP that allows developers to declare, install, and update the libraries and packages their projects depend on. It manages these dependencies through a composer.json file, resolving version conflicts and autoloading classes automatically. It is the standard package manager for the PHP ecosystem, similar to npm for JavaScript or pip for Python.
Developers should use Composer when working on PHP projects to streamline dependency management, ensure consistent environments across development and production, and leverage the vast ecosystem of packages from Packagist. It is essential for modern PHP development, including frameworks like Laravel, Symfony, and WordPress plugins, as it simplifies installation, updates, and autoloading of third-party code.