.. SPDX-License-Identifier: CC-BY-4.0
   Copyright 2026 The Linux Foundation

SPDX License IDs
================

Use SPDX short-form identifiers to communicate license information in a simple, efficient, portable and machine-readable manner.

Key takeaways and best practices
--------------------------------

* Add an SPDX license ID single-line comment to every source file, wherever reasonably possible.
* Use ``AND``, ``OR``, ``WITH`` and ``+`` operators to communicate combinations of licenses.
* For license texts that aren't on the SPDX License List, use ``LicenseRef-`` and ``AdditionRef-`` to create your own custom IDs.

Overview
--------

A project's license information can be challenging to track, because it may be stored in many different locations, such as:

* a LICENSE text file in the project's root directory
* metadata for the project's entry with a package manager
* a written text description in a README file
* a written text description in one or more source code files
* and other places...

In addition, particular files may have a license that differs from the project's "overall" license in its LICENSE file; or may have different licenses based on their location or document type.

To help with making license information more human- and machine-readable, use **SPDX short-form license IDs** in your source code (and other) files. These consist of a single line in the form described on the following pages.

Details
-------

.. toctree::
   :maxdepth: 1

   Format <spdx-license-ids-format>
   OR Expressions <spdx-license-ids-or>
   AND Expressions <spdx-license-ids-and>
   WITH Expressions <spdx-license-ids-with>
   () (parentheses for grouping) <spdx-license-ids-parentheses>
   + Expressions <spdx-license-ids-plus>
   Custom License IDs <spdx-license-ids-custom>