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Repair common Windows errors and clear accumulated junk for a smoother, more stable PC - no reinstall needed.Free scan · no reinstallAdd a one-line SPDX-License-Identifier: comment near the top of each source file your project policy covers. Use the exact identifier or license expression from the current SPDX License List, and keep the full license text and required notices in the repository. The tag makes a file’s declared license easier to identify and process; it does not establish that the declaration is legally correct.
What an SPDX license ID does
An SPDX file header is concise license metadata attached to an individual file. That matters when code is copied or reused outside its original repository: the declaration travels with the file instead of relying only on someone finding the project’s top-level license document.
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SPDX Annex E says the tag declares the license a file is under and should appear at or near the top of the file in a comment. It must be on one line and may contain a single identifier or a compound license expression. The SPDX specification, in Annex H, explains that the distinctive standard string is intended to be easy for software tools to detect.
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How to write the header
Put the tag in the file’s normal comment syntax, with the expression on a single line:
SPDX-License-Identifier: MITFor example, in a language that uses C-style comments, the line could be written as // SPDX-License-Identifier: MIT; in a language with hash comments, use # SPDX-License-Identifier: MIT. The tag text and license expression are the same; only the comment marker changes. Consult the SPDX License List for exact identifiers. The list page reports version 3.29.0 dated 2026-09-16; check the current registry rather than assuming an identifier or its status remains unchanged.
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Choose the right expression for multiple terms
SPDX expressions use uppercase operators to communicate how terms relate. Select an expression that matches the actual license grant for the file; do not add an operator simply because it seems convenient.
| Situation | Example | Meaning |
|---|---|---|
| One listed license | SPDX-License-Identifier: MIT |
The file is declared under the MIT license. |
| Alternative licenses | SPDX-License-Identifier: GPL-2.0-only OR MIT |
The stated alternatives are available; OR expresses a choice. |
| Cumulative terms | SPDX-License-Identifier: LGPL-2.1-only AND BSD-2-Clause |
The expression declares that both sets of terms apply. |
| License with a listed exception | SPDX-License-Identifier: GPL-2.0-or-later WITH Bison-exception-2.2 |
WITH attaches the named exception to the license. |
An exception is not a stand-alone license: use it with the applicable license through WITH. Keep every expression on one line, and copy license and exception names exactly as listed. If no SPDX-listed license fits, a documented LicenseRef-... can identify a non-listed license; include or point reviewers to the referenced license text so its terms can be resolved.
Roll out file identifiers without guessing
- Set coverage. Inventory source, generated, test, documentation, and vendored files. Decide which categories your policy requires to carry file-level tags; not every repository will treat every category alike.
- Establish provenance. For each covered file, check project history, existing headers, contributor agreements, and third-party notices to determine the governing license. A neighboring file’s tag is not proof that the terms match.
- Map terms to SPDX. Find the exact current identifier in the SPDX License List. If a file has multiple terms or an exception, construct the expression that represents them; do not guess from a similar license name.
- Add the comment near the top. Use the language’s comment marker and put
SPDX-License-Identifier:plus the complete expression on one line. - Retain full texts and notices. Keep the complete license text in the repository’s
LICENSEfile or applicable notices directory. A short identifier does not replace those materials. - Check and maintain. Add CI or review checks for malformed, unknown, or contradictory identifiers and for required license texts. Revalidate identifiers when dependencies, license versions, or SPDX data change.
What the tag can—and cannot—automate
A consistent tag gives scanners and other tools a predictable string to detect, helping teams identify declared file-level terms, produce reports, and review license coverage. A policy can also make omissions visible by checking which in-scope files lack a tag.
Detection is not legal verification. A syntactically valid identifier may still be wrong if the file’s history, contributor terms, upstream license, or exception does not support it. An SPDX header also does not replace full license texts, attribution, copyright notices, or other obligations. For generated and vendored files in particular, determine whether the original declaration and notices must be preserved before changing or adding a header.
For teams with large codebases, open-source license-scanning and compliance tools can help detect and report declarations, but they do not remove the need to validate provenance and policy. The core control remains a correct mapping from each file to its actual terms, backed by retained notices and reviewable checks.
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