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Adding a license to a project is essential for making it reusable: In the absence of other agreements, in fact, copyright law would otherwise forbid others from (re-)using and distributing your work. Moreover, a license can further specify other important properties, such as the temporary- or forever-openness of the code, the rights granted to the users (such as the four fundamental software freedoms), or the permission of using patents encoded in a program.
The international validity of most common licenses is guaranteed by copyright law, and in particular by the Copyright Treaty of the United Nations' (UN) World Intellectual Property Organization (WIPO) adopted in 1996. This treaty sets a common denominator for all adhering countries, but individual countries can still extend domestically the reach of copyright. The article 4 of the Copyright Treaty clarified once for all that computer programs are protected by copyright just as literary works. Unfortunately, however, copyright law does not protect hardware objects.
Copyright law is extremely powerful. In fact, it grants the author of a work exclusive rights to use or distribute their work. An author can grant permission of using his/her work under arbitrary conditions; just for illustration, an author could invent for example a "coffee license" and impose that whoever uses his work has to offer the author a coffee. Similarly, forever-open licenses grant users the right to use the work provided that they will redistribute any derivative work using the same license again (copyleft).
If you start a new software project, the diagram below can help you quickly decide on which free software license to choose. If you need a license for a non-software project, you can skip this section. Later sections will explain the different choices in more details.
Do you either want to allow people to create proprietary (closed-source) projects with your code, or do you expect your project to remain small (e.g. less than 300 lines)?
In order to correctly license your work, you have to explicitly tell which files of your work are under which license, and how to find the full license text. We recommend to follow these steps to avoid ambiguities:
One of the major distinctions between licenses is between:
Licenses which guarantee the perpetual openness of the code, i.e. forever-open licenses. This is commonly obtained by a mechanism called "copyleft" which requires redistributing any derivative work using the same license again. The GPL licenses belong to this category. Other mechanisms to achieve the perpetual openness of the code include contractual law, but that is rarely used for software licenses.
Licenses which permit to close the source, i.e. temporarily-open licenses. These licenses are usually known as permissive licenses. The MIT license or the Apache license belong to this category. The term "permissive" often causes confusion, because it sounds fair and good to unexperienced people. People who contribute to the development of a program released with a permissive license must be aware that the program could become proprietary at any time. For example, when a company hires the original team of developers.
If all copyright holders agree, a project can always be forked into a project with a different license. Therefore, the larger the number of developers, the more difficult it is to make such a change.
There is no general rule for choosing one type of license or the other in every situation, but we encourage using copyleft licenses whenever possible.
Free software licenses are licenses which respect the four fundamental software freedoms defined by the Free Software Foundation. Both copyleft and permissive license can, or cannot, be free licenses. For example, the Modified BSD license is a permissive non-copyleft free software license.
In the context of licenses, the term "free" means free as in "freedom", not of gratis, but this has often been confused. Still, free software is often also gratis software. Gratis non-free software usually includes gratis proprietary programs (shareware), demonstration or trial versions, limited versions (crippleware), advertising-supported software (e.g. antivirus), and usually viruses and worms (the victim doesn't pay to get them).
Some permissive/temporarily-open licenses like the MIT license do not contain a patent provision granting the users the right to use their patents. For example, the code might be licensed under the MIT license, but implements an algorithm which is protected by a patent. In this case, the license might allow to copy, modify and distribute the code but at the same time does not guarantee the right to use the patented algorithm. It is a common argument in favour of the MIT license to claim that no public lawsuit has ever been conducted yet. Still, the threat to be sued remains, and it can be used to exert pressure. Some, if not most, license disputes moreover are settled even before reaching the court and could therefore leave no trace. Even Google avoided the use of the MIT license when developing Android, presumably because of the missing patent provision.
For further information on "patents and free software", head over to this wikipedia article.
Over the years, hundreds of different software/artwork licenses have been written, used and abandoned. This causes a big harm to the Free and Open Source community because it makes it more difficult for everybody to understand their meaning and compatibility between them. A common reaction of developers is to refuse discussions about licenses or their use altogether. Rather than dispersing efforts in a multitude of isolated and incompatible efforts (license proliferation), we recommend using whenever possible only the mainstream licenses as highlighted in this page.
It can occur that different projects, licensed with different open-source licenses, cannot be used together in a single, often larger, project because the licenses require incompatible conditions. Some licenses, in fact, impose on developers (thanks to the power granted by copyright law) some restrictions/obligations on any derivative work. The term "derivative work" has a precise meaning in copyright law: For example, when developers modify the source code written by somebody else, they have created a derivative work. As an example, if program A is licensed under GPL version 3 and program B is licensed under the Microsoft Public License (MS-PL), the GPL requires to re-license any derivative work based on both programs A and B again under GPL, while the MS-PL requires to re-license the derivative work under MS-PL: the two conditions are incompatible with each other. The incompatibility between licenses is clearly a headache for every developer. A possible way out, and the one we recommend, is to use only mainstream licenses (as recommended in this page) and hence avoid license proliferation. For more information on license compatibility, we recommend the commented license list curated by the GNU project.
The open-source community is represented by a variety of groups with different, and sometimes opposite, interests. For example, the prominent websites ChooseALicense.com is curated by GitHub and can be assumed to reflect at least partially the interests of Microsoft; this website presents, for example GPL last on the front page and it is silent about the missing patent clause in the MIT license both in the front page and in the dedicated page. Moreover, the wording "I want it simple and permissive" can induce people to favour the MIT license; laypeople will want to have legal matters simple, and "permissive" sounds like fair and good. When reading articles on licenses (including this one), we recommend exercising discretion by inspecting the governance of the source and the risk of conflicting interests.
A contributor license agreement may be forced upon a developer (e.g. by an employer), and may contain clauses which effectively void the spirit of certain open-source licenses. For example, a single company may advertise a project (for example for marketing reasons) under a GPL license, but on the other hand could require all its contributors to assign their copyright to the company. In this way the company could at any time (by being the only copyright holder) change the license from GPL to a proprietary license.
For software projects, we recommend whenever possible to utilize a copyleft license. The only well-established licenses of this type are those of the GNU General Public License (GPL) family. The GPL licenses have evolved over time and come with different versions. Unfortunately, some versions are not compatible with older ones. To avoid license proliferation and to ease compatibility with future versions, we recommend using the "GNU Affero General Public License v3.0 or later" with SPDX license identifier "AGPL-3.0-or-later". The AGPL provides the maximum openness of the code: Even when the software runs on a server, users who interact with that software (e.g. over a network connection) are entitled to receive a copy of the source code. The Affero GPL v3.0 is compatible with the GPL v3.0 and vice-versa thanks to article 13 in each license.
If using AGPL-3.0-or-later is not an option, we recommend using another license of the GNU family, such as the General Public License (GPL), or the Lesser General Public License (LGPL), always indicating the version "v3.0 or later". In some cases, such as when writing certain libraries, using the Lesser General Public License (LGPL) may lead to a broader usage. In such cases, the LGPL is preferred over the (A)GPL. For software which is not very long (e.g. less than 300 lines of code) or unimportant, rather than using a copyleft license you may consider using a lax permissive license instead.
If you are not allowed to, or if you do not want to use a forever-open license (for example because the company you work for does not allow you to do so) we recommend using a temporarily-open or permissive (in the sense that it permits users to close source the code) license which contains a patent provision. To avoid proliferation of licenses, we recommend therefore to use the Apache license version 2.0 (SPDX license identifier Apache-2.0).
We recommend following the guidelines defined by the GNU project. They are recommended by the Free Software Foundation, too.
We distinguish primarily between two families of hardware projects:
In the first case, we recommend the use of the CERN Open Hardware License Version 2 - Strongly Reciprocal (SPDX license identifier: CERN-OHL-S-2.0). This license guarantees the forever-openness of the project as well as the actual hardware objects, but is incompatible with other mainstream licenses like those of the GNU-GPL family.
In the second case, there is currently no copyleft/forever-open license with wide license compatibility which is able to protect a hardware device. This is primarily due to the fact that hardware objects are not protected by copyright law. While awaiting for the appearance of a suited license, we recommend the use the "GNU Affero General Public License v3.0 or later" whenever the use of a CERN Open Hardware License is not permitted.
For hardware projects which should allow creating proprietary forks and/or proprietary hardware objects a license can be used as described in the next section.
For documentation, writing, and other non-code assets, a Creative Commons (CC) license can be used, but note that only the following CC licenses are considered free (sorted from protective to unconditional):
Like CC themselves, Codeberg recommends against using a CC license on code.
We do not curate our own FAQ. Instead we redirect to other major collections:
If you have further questions on licensing, feel free to reach out to our community Matrix channels. Access links are provided at the contact page.
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