Can the permission to implement a specification be restricted?
<p>Let's say I invent a new image file format and release the specification to the public. Is it possible to only allow GPL projects to implement this specification?
Or is this not possible in the U.S.? (Because the national laws do not allow something like this. To keep it simple let's assume we are in the U.S.)</p>
<p>There is a similar question <a href="https://law.stackexchange.com/questions/80194/copyrightability-of-third-party-technical-specifications">here</a> but it is not the same because it is about a reverse-engineered file format.</p>

<p>Unless you have a legally valid IP right related to the specification that statement is meaningless. When a software license is granted it is based on the copyright of the code. The copyright of the spec. just stops people from copying the spec - it does not protect the information in it.</p>
<p>You can restrict copying of the spec. under copyright, you can make up a name for the spec (like USB or Bluetooth) and get a trademark and only allow the trademark use in limited cases(doesn’t stop implementation of the spec), or get a patent that would be necessarily infringed if something complying with the spec was created and used, sold, made, etc. or you can keep it secret and only show it to people who contractually agreed with your terms.</p>

licensing gpl