Introduction to Composer | Archived 2.3 Magento Developer Guide

We use Composer to manage Magento components and their dependencies. Using Composer to get the Magento software metapackage provides the following advantages:

Reuse third-party libraries without bundling them with source code
Reduce extension conflicts and compatibility issues by using a component-based architecture with robust dependency management
Adhere to PHP-Framework Interoperability Group (FIG) standards
Repackage Magento Open Source with other components
Use the Magento software in a production environment

You can also download an archive file for a specific version of Magento in either ZIP or TAR format. Installing Magento from an archive lacks the advantages of using Composer. Contributing developers should use the git-based installation method.

Links to Magento code

The key to developing any Magento component is its composer.json, which specifies version and dependency information for a component, among other things. You can look at Magento 2 code, such as:

Metapackage, look at <magento_root>/composer.json.
Customer module
Luma theme
en_us language package

For more information

For more information about Composer, see the Composer documentation.