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API Copyleft License 1.0.0first release of API-boundary copyleft form

I’m happy to announce the 1.0.0 release of the recently rechristened API Copyleft License.

This was only possible with wonderful feedback from several people:

Looking forward to more proposals and discussions on GitHub. Version 1.0.0 is a good license. But like all the license I work on, I expect that it will continue to evolve.

The text of version 1.0.0 follows:

API Copyleft License

Version 1.0.0

Developer: {Legal Name}

Homepage: {URL}


This license gives you permission to use, share, and build with this software for free, but requires you to contribute source code for changes, additions, and software that you build with it, other than applications.


As far as the law allows, this software comes as is, without any warranty, and the developer will not be liable to anyone for any damages related to this software or this license, for any kind of legal claim.


In order to receive this license, you must agree to its rules. Those rules are both obligations under our agreement and conditions to your license. You may not do anything with this software that triggers a rule you cannot or will not follow.

The developer licenses you to do everything with this software that would otherwise infringe copyrights in this software they can license.


The developer licenses you to do everything with this software that would otherwise infringe any patent claims they can license.


The developer will not revoke this license.


You must ensure that everyone who gets a copy of any part of this software from you, in source code or any other form, also gets the text of this license, including its developer and homepage lines.


With two exceptions, Prototypes and Applications, you must contribute all software that invokes this software’s functionality, as well as changes and additions to this software, according to Contributing.


You need not contribute prototype changes, extensions, or applications that you do not end up using for more than fourteen calendar days, share with anyone else, or use to provide a service to anyone else.


You need not contribute software that only invokes this software’s functionality through the interfaces this software exposes, without exposing this software’s interfaces and functionality to other software.

Interfaces exposed by this software include all the interfaces this software provides users or other software to invoke its functionality, such as command line, graphical, application programming, remote procedure call, and inter-process communication interfaces.


When this license requires you to contribute software:

First, publish all source code for that software, in the preferred form for making changes, through a freely accessible distribution system widely used for similar source code, so the developer and others can find and copy it.

Second, ensure that each part of that source code is licensed to the public under one of these:

  1. The BSD-2-Clause Plus Patent License

  2. terms with substantially the same legal effect as Copyright, Patent, and Reliability, and optionally a rule like Notices, a disclaimer like Disclaimer, or both, but no other terms

  3. this license

Take these steps within thirty calendar days of creating or using the software for the first time.


You are excused for unknowingly breaking Notices or Copyleft if you do what the rule requires, or stop doing anything requiring this license, within thirty days of learning you broke the rule.

Your thoughts and feedback are always welcome by e-mail.

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