Tool · Compatibility
Licence compatibility.
Check whether material under two different open licences can be legally combined — what attribution flows, what share-alike obligations propagate, and where the combination produces a more-restrictive result than either licence on its own.
What "compatibility" actually means
Two open licences are compatible when material under one can be combined with material under the other, and the resulting combined work can itself be redistributed under a single licence (or under a small, well-defined set of licences) without violating either source licence's terms.
Compatibility is asymmetric. Licence A can be one-way compatible with Licence B (meaning content from A can flow into B-licensed projects but not vice versa) without B being compatible back with A. Creative Commons 4.0 maintains an explicit one-way-compatibility list — the GNU Free Documentation Licence and the Free Art Licence are listed as one-way compatible destinations for CC BY-SA content, for example.
The four compatibility outcomes
Most pairwise combinations of open licences produce one of four outcomes, and naming them is half the work:
- Cleanly compatible. The combined work can be released under either source licence (or a third licence the source licences are both one-way-compatible into). Attribution from both sources must be preserved but no new restrictions are introduced. CC BY 4.0 and OGL Canada 2.0 are an example.
- Compatible with share-alike propagation. The combined work can be released, but only under the more-copyleft of the two source licences. This is the normal outcome when combining a permissive licence with a copyleft one — for instance, combining CC BY data into an OpenStreetMap-derived database under ODbL produces an ODbL-licensed combined database with the CC BY attribution preserved.
- Compatible only for private use. The combination is permitted internally — for analysis, research, or in-house workflows — but the combined work cannot be redistributed because no single licence covers it. Combining an open dataset with a NonCommercial Creative Commons dataset typically produces this outcome if the combined work is intended for unrestricted redistribution.
- Incompatible. The combination is not permitted at all. The most common case is combining two copyleft licences that each require their own licence terms to govern derivatives — neither licence's share-alike requirement permits the other's terms.
Where the analysis lives in CLIPol
Each licence's Compatibility tab — for example, the compatibility view for the GeoBase / Canada family or for the Open Government Licence — Canada — lists the licences that combine cleanly with it, the licences that combine with share-alike propagation, and the licences with which a combination is incompatible for redistribution.
The hardest cases
Three combinations are recurringly hard in practice:
- Mixed CC-NC stacks. NonCommercial CC licences combine permissively among themselves but the downstream commercial-use restriction propagates aggressively. Combining a single CC-NC source into a broader open-data project effectively makes the entire combined work non-commercial. The petermr blog post on interconverting CC-NC licences (from the Cambridge chemistry research group) is the most-cited examination of this problem.
- Database rights vs copyright. In EU jurisdictions, databases are governed by both copyright (covering the structural arrangement) and the sui generis database right (covering substantial extraction and reuse). Older Creative Commons versions handled the database right inconsistently. CC 4.0, the Open Data Commons family (PDDL, ODC-BY, ODbL), and most post-2013 government open licences address both rights explicitly, but combining material under pre-4.0 CC licences with material under explicit database licences still requires careful reading.
- Government licences and copyleft. Most national open-government licences (OGL UK, OGL Canada, the Licence Ouverte, the New Zealand framework) are permissive attribution licences and are cleanly compatible with CC BY. Combining them with ODbL or CC BY-SA is permitted but the resulting combined work falls under the copyleft licence's share-alike terms.
What CLIPol is not
CLIPol's compatibility tool is a working reference — a good starting point for understanding the landscape and for sanity-checking a combination decision before committing to it. It is not a substitute for legal advice. For a specific combination decision in a real project, particularly a project that will be redistributed at scale, the original licence texts are the authoritative source and a lawyer with subject-matter familiarity is the appropriate adviser.