Choosing a Composer‑Based Extension Bundle vs Classic Local Extension in Contao 5/6

Decision and Constraints

The task is to add a custom backend module to Contao. The clear decision is to use a Composer‑based Extension Bundle, or fall back to a classic local extension. Constraints: Contao version 5.5 or higher (including 6.x), PHP 8.0+, no direct edits to core files, Composer must be available for dependency management, and the module must be registerable through the Extension Management Console.

Option Comparison

Aspect	Composer Bundle	Classic Local
Location	Project directory, installed via Composer	Contao packages/extension/ folder
Update method	Composer require/update, lock file	Manual copy/replace of files
Dependency handling	Composer resolves packages, can use Symfony components	None; only core Contao APIs
Compatibility	Works with Contao 5.5+ / 6.x, PHP 8.0+	Limited to core APIs, may break with future Contao releases
Deployment effort	Composer install step, requires write access to project directory	Simple copy, but manual updates required