What is a submodule?

A Git submodule allows one Git repository to be used as a separate repository inside another repository. The parent repository does not directly include the submodule's entire history; instead, it stores a reference to a specific commit in the submodule. This lets you use a shared library or independent project within another project.

project/
├── app/
└── libraries/
    └── shared-ui/

A submodule has its own Git history and working directory. It can be updated independently of the parent repository.

A parent repository containing a submodule records which commit the submodule should use. The nested repository keeps its own files and commit history separate. When you create a new commit inside the submodule, you must also record the updated submodule reference in the parent repository.

git status
# modified: libraries/shared-ui (new commits)

This structure helps you keep dependent projects on specific versions.