Common events for Composer plug-in include init, command, pre-file-download, post-install-cmd, post-update-cmd, pre-autoload-dump and post-autoload-dump. Init is used to initialize configuration and register repositories; command is used to log or verify before command execution; pre-file-download can be used to modify download URLs or use cache; post-install-cmd and post-update-cmd are used to run cleaning or deployment tasks after installation or update; pre-autoload-dump and post-autoload-dump are used to generate dependent files or response changes before and after automatic load generation. Understanding these events helps to develop efficient Composer plugins.

Composer plugins can hook into various events during the execution of Composer commands. These events allow plugins to modify or extend Composer's behavior at specific points in the process. Understanding these events is key to developing or debugging Composer plugins.

Here are some of the most commonly used Composer plugin events:

1. init – When the Composer instance is initialized

This event is triggered very early in the Composer lifecycle, right after the Composer instance is created but before any command logic runs. It's useful for setting up initial configurations or registering custom package repositories.

• This is a good place to register new repository types or modify the configuration before anything else happens.
• Plugins that need to alter the way packages are loaded often use this event.

2. command – Before a Composer command runs

The command event fires just before a specific Composer CLI command starts executing. This allows plugins to perform actions based on which command is being run (like install , update , etc.).

• You can inspect the command name and arguments.
• Useful for logging, pre-validation, or setting internal flags depending on the command.

3. pre-file-download – Before downloading files (eg, packages)

This event is triggered every time Composer is about to download a file — such as a package zipball or a remote JSON file from a repository.

• Allows plugins to intercept and modify download URLs or even provide cached versions.
• Often used for custom authentication or routing downloads through a proxy.

Example: If you're behind a corporate firewall, a plugin might rewrite download URLs to go through an internal mirror.

4. post-install-cmd and post-update-cmd – After install/update completes

These events fire after composer install or composer update finishes. They're among the most commonly used events for running post-processing tasks.

• Commonly used to trigger scripts like clearing caches, dumping autoloads, or notifying external services.
• These events behave similarly to the scripts section in composer.json .

You can attach multiple handlers to either of these events to perform cleanup or deployment-related actions.

5. pre-autoload-dump and post-autoload-dump – Around autoloader generation

These events are triggered around the autoloader generation step, which happens during install, update, or when explicitly asked via dump-autoload .

• Use pre-autoload-dump if you need to generate files required by the autoloader.
• Use post-autoload-dump if you want to react to the autoloader being updated.

For example, a framework might generate a class map or route cache during pre-autoload-dump .

There are other less common events too, such as pre-command-run , pre-archive-dump , and more, but the ones above cover most practical plugin development needs.

If you're building or working with Composer plugins, knowing which event to hook into makes a big difference in how effective your plugin can be. Just make sure to only bind to the events you actually need — unnecessary hooks can slow things down.

Basically that's it.

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