PHP Dependency Manager

A dependency manager for the PHP programming language, currently at version 2.10.1, that revolutionized PHP development by introducing modern package management practices to a language ecosystem that previously relied on manual file inclusion and version management. The tool resolves and installs project dependencies declared in a composer.json file, which specifies required packages with version constraints using semantic versioning operators including caret for compatible updates, tilde for patch-level updates, and exact version pinning. The dependency resolver analyzes the full transitive dependency tree, resolving version conflicts using a SAT solver that finds the best combination of package versions satisfying all constraints simultaneously. A lock file records the exact versions of all installed packages including their checksums, ensuring reproducible installations across development, staging, and production environments. The autoloader generates an optimized class-to-file mapping supporting PSR-4 and PSR-0 namespace conventions, classmap generation for non-conforming libraries, and fallback file scanning, providing zero-configuration class loading without manual require statements. The Packagist repository serves as the primary package registry hosting over 400,000 packages, with mirrors and private repositories supported through authentication and custom repository types including VCS, path, package, and artifact. The tool handles both project-level dependencies and global installations for CLI tools and utilities. Scripts hooks execute custom commands at lifecycle events including pre-install, post-install, pre-update, and post-autoload-dump, enabling database migrations, cache clearing, and asset compilation as part of the dependency update workflow. Created by Nils Adermann and Jordi Boggiano, the project is MIT licensed with commercial support available through Private Packagist.