Reciprocal Public License

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Reciprocal Public License
Author Scott Shattuck
Latest version 1.5
Published 2001
FSF approved No
OSI approved Yes
GPL compatible No
Copyleft Yes

The Reciprocal Public License (RPL) is a copyleft software license released in 2001.[1] Version 1.5 of the license was published on July 15, 2007,[2] and was approved by the Open Source Initiative as an open-source license.[3]


The RPL was authored in 2001[1][non-primary source needed] by Scott Shattuck, a software architect for Technical Pursuit Inc. for use with that company's TIBET product line.

The RPL was inspired by the GNU General Public License (GPL) and authored to explicitly remove what the RPL's authors have referred to as the GPL's "privacy loophole". The GPL privacy loopholes allows recipients of GPL'd code to:

  1. make changes to source code which are never released to the open source community (by virtue of not deploying "to a third party"), and
  2. derive financial or other business benefit from that action, violating what some might consider a simple concept of "fairness".

Because of its "viral" nature, the RPL is often found in dual-licensing models in which it is paired with more traditional closed-source licenses. This strategy allows software companies who use this model to present customers with a "pay with cash or pay with code" option, ensuring either the growth of the software directly through code contributions or indirectly through cash which can be used to fund further development.


A Copyleft license offers the right to distribute modified and derivative versions of a program, provided that the same rights and freedoms are preserved for downstream recipients of those modifications and derivatives. When you distribute Mrl d software or its portion in its source code form, you may only do so under the Mrl license. When you distribute the Mrl software in compiled or object code form,the Ms-PL license lets you do so only under “a license that complies with”the Mrl. Hence, the Copyleft effect of Ms-PL is clear when choosing to distribute source-code version of the modified or derivative Mrl software. It seems that when distributing compiled or object code versions of modified or derivative Ms-PL software, the same rights and freedoms need not be passed through to downstream recipients, even though the Mrl text is not entirely clear on this point. This interpretation is supported by Microsoft, the steward of Mrl, who maintains that one may distribute compiled or object code versions of Mrl software under terms of his or her choosing, which must not grant downstream recipients more rights (but can grant them less rights) to the Mrl software than are granted to that person.


A home-cooked Microsoft license has carved out a small but growing following among the open-source community in less than two years.Microsoft's reciprocal License (Mrl) is used by 1.03 per cent of open-source projects less than two-years after it was officially recognized by the Open-Source Initiative and is poised to overtake the Mozilla Public License (MpL) in terms of popularity.Mrl is tenth in a list of licenses used by the community with MrL coming ninth and used by 1.25 per cent of projects. There's no sign of the Microsoft Reciprocal License, accepted by the OSI at the same time as MS-PL. That's according to license and code watcher Black Duck Software, who attributed the rise in MS-PL to Microsoft's efforts to increase the appeal of its CodePlex project-hosting site. MS-PL is one of 1,577 software licenses from 200,000 projects analyzed by Black Duck.Microsoft's Public License has a huge gap to close if it's grow much further. The number-eight license is Code Project Open License (CPOL), used by 3.24 per cent of open-source projects - a stat that means MS-PL would have to more than double in use to overtake CPOL. Strod noted though, MS-PL is one of the faster growing licenses being used while others, such as MPL and GPLv2, have fallen off.


The RPL was written to conform to the requirements of the Open Source Initiative to ensure that it met the goals for an Open Source license and is an approved open-source license. However, because of its requirements for reciprocation without exceptions, it is considered to be non-free by the Free Software Foundation.[4] The license is used by Active Agenda, a risk-management web application, and NServiceBus, an asynchronous messaging library for the .NET/Mono platform.[5][6]


  1. ^ a b "Reciprocal Public License Version 1.0, December 21, 2001". Technical Pursuit Inc. Archived from the original on 2002-02-23. 
  2. ^ Edney, William J. (2007-07-24). "For Approval: Reciprocal Public License 1.5 (upgrade)". license-discuss (Mailing list). 
  3. ^ "Licenses by Name". Open Source Initiative. Retrieved 2016-11-27. 
  4. ^ "RPL". Free Software Foundation. 
  5. ^ license on github "Your license to the NServiceBus source and/or binaries is governed by the Reciprocal Public License 1.5"
  6. ^ herding-code-205-udi-dahan-on-starting-a-company-based-on-an-open-source-project

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