Installing Your First Composer Package

Use composer require to add a package to composer.json, install it in vendor and load its API through vendor/autoload.php.

What It Does

A project dependency should be declared and its installed version inspected. Review which packages are direct dependencies. Install the exact locked versions and verify the target PHP runtime. Review which packages are direct dependencies.

Requirements and Compatibility

Use a supported PHP runtime and install any third-party tool or extension explicitly shown in the examples. Commands should be run from the project root unless stated otherwise.

Syntax, Inputs and Results

The examples separate configuration, the smallest working operation and a realistic follow-up task. Adapt file paths and dependency versions to your own project.

Example 1: Basic Use

A project dependency should be declared and its installed version inspected. Review which packages are direct dependencies.

composer require monolog/monolog
composer show monolog/monolog
composer show --direct

Example 2: Another Case

Install the exact locked versions and verify the target PHP runtime. Review which packages are direct dependencies.

composer install --no-interaction --prefer-dist
composer check-platform-reqs
composer show --direct

Practical Example

Validate package metadata and build optimized autoload maps. Review which packages are direct dependencies.

composer validate --strict
composer dump-autoload -o
composer show --direct

For production, apply the compatibility and edge-case limits described below.

Important Behavior and Edge Cases

Use the checked-in lock file for reproducible application builds.

Comparison with Related Functions and Tools

Subject	Key difference
composer install vs composer update	install follows composer.lock; update resolves new versions and updates the lock file.

Common Beginner Mistakes

Mistake	Correct approach
Treating a version range as a fixed installed version	Commit composer.lock for applications and run composer install in deployment.
Skipping the prerequisite of this specific workflow	Install or configure the named tool and confirm the example can actually run.
Ignoring edge conditions	Use the checked-in lock file for reproducible application builds.

Key Takeaways

Use composer require to add a package to composer.json, install it in vendor and load its API through vendor/autoload.php.
Use the checked-in lock file for reproducible application builds.
Keep application configuration, source code and validation tests under version control.

Use these examples as a starting point, then validate the result with the actual PHP build, dependencies and inputs used by your application.