Creative Commons License Validator

Creative Commons license identifier: the six combinations plus CC0

Creative Commons (CC) is a set of standardised public-copyright licenses created in 2001 by Lawrence Lessig, Hal Abelson and Eric Eldred at Harvard. They let authors keep copyright while pre-authorising specific reuses — copy, share, remix, commercial use, derivatives — without case-by-case negotiation. Today CC licenses power Wikipedia, Flickr Commons, OpenStreetMap, Unsplash (until 2017), the open-access scientific journals (PLOS, eLife), and over 2 billion works worldwide. Validating a CC identifier means confirming the string matches one of the canonical short forms and a known version number.

CC licenses are described by an SPDX-style short form (e.g. CC-BY-SA-4.0) and by a canonical URL on creativecommons.org/licenses/<code>/<version>/. Both forms are accepted as references in repositories, datasets and metadata.

The six main licenses plus CC0

• CC BY — Attribution. Anyone can reuse, including commercially and with modifications, as long as the original author is credited.
• CC BY-SA — Attribution + ShareAlike. Same as BY, but derivative works must be released under the same license. Used by Wikipedia and OpenStreetMap.
• CC BY-NC — Attribution + NonCommercial. Free use only for non-commercial purposes.
• CC BY-ND — Attribution + NoDerivatives. Commercial use allowed, but the work cannot be modified.
• CC BY-NC-SA — Attribution + NonCommercial + ShareAlike.
• CC BY-NC-ND — Attribution + NonCommercial + NoDerivatives. The most restrictive.
• CC0 — public-domain dedication. The author waives all copyright as much as legally possible. Useful in jurisdictions like Germany or Brazil where pure public-domain dedication is not formally recognised.

Two retired/historic variants you may still see: CC BY 1.0 "Sampling" (defunct) and CC PDM (Public Domain Mark, used for already-PD works, not a dedication).

License versions: 1.0 to 4.0

CC licenses exist in five versions: 1.0, 2.0, 2.5, 3.0 and the current 4.0. The 4.0 family — released in 2013 — was the first version not ported to local jurisdictions: it is jurisdiction-neutral by design and explicitly covers database sui-generis rights (relevant in the EU). Older versions, such as CC-BY-3.0-BR, are still in circulation for legacy works but should not be used for new content. SPDX recommends the canonical identifiers CC-BY-4.0, CC-BY-SA-4.0, ..., and CC0-1.0 for the public-domain dedication.

Compatibility, mixing and commercial use

CC licenses are not always inter-compatible. A few key rules:

• SA is "viral": a derivative of a BY-SA work must itself be BY-SA (or compatible — CC 4.0 explicitly lists GPLv3).
• ND blocks remixes: you cannot combine a BY-ND work into a larger derivative.
• NC blocks commercial reuse — including ads, paid courses, books for sale.
• CC0 and BY are compatible with virtually everything, including proprietary code/content.

CC does not waive patents or trademarks — those are governed by separate law. CC also does not address moral rights in jurisdictions where they exist (France, Brazil); attribution remains mandatory regardless.

Validation: regex, URLs and SPDX

A practical validation regex for the short form is:

^CC(0-1\.0|(-BY)(-NC)?(-SA|-ND)?-(1\.0|2\.0|2\.5|3\.0|4\.0))$

The canonical URL pattern is https://creativecommons.org/licenses/<code>/<version>/ (e.g. https://creativecommons.org/licenses/by-sa/4.0/) or https://creativecommons.org/publicdomain/zero/1.0/ for CC0. Brazilian sites such as the Domínio Público portal (gov.br) and Globo's open-content pages use this URL form. AI training: from 2023 onwards, courts and CC itself have been clarifying whether CC-licensed works can be used to train ML models — the answer depends on attribution and on whether the model itself counts as a derivative.

FAQ

Can I use a CC-licensed work commercially?

Yes for CC0, CC BY, CC BY-SA and CC BY-ND. No for any license containing the NC clause. Attribution is still required for everything except CC0.

Can I mix two different CC licenses in one work?

Carefully. Two BY-SA works can be combined under BY-SA. A BY work can be reused inside a BY-SA composite. ND blocks remixing entirely. NC blocks combination with any non-NC composite if the result is commercial. The official Creative Commons compatibility chart is the authoritative reference.

Is CC0 the same as public domain?

Almost. CC0 is an explicit dedication: the author waives all copyright "to the extent allowed by law", and adds a fallback unconditional license for jurisdictions where waiver is not legally possible (Germany, Brazil). For practical purposes treat CC0 as public domain — the original author keeps no claim.

Which CC version should I use today?

Always 4.0 (or CC0 1.0 for the public-domain dedication). It is jurisdiction-neutral, explicitly covers database rights, and is recognised by SPDX as CC-BY-4.0, CC-BY-SA-4.0, and so on. Older versions (3.0 and below) should be kept only for legacy works.