Rewriting a library licensed under AGPL but keeping the public interface

Question

We need a JSON Schema Validator for .NET. The only library that we found is Newtonsoft Json Schema. The problem with this library is that has a "strange" AGPL license with limitations, from the site:

AGPL 3.0 : Free with limitations (1000 validations per hour)

Otherwise we should get a commercial license for each developer. Maybe the management will decide to buy the commercial license but my question is:

If we decide to rewrite it, it is fine/legal to use the same API interface? Basically rewriting all the actual validating code but keeping the same public method and properties name (changing only the namespace).

In other words is the interface of a library also under the AGPL license or only the implementation/algorithm?

Answer 1

For the record: a "Modified AGPL" that includes that limitation is not AGPL anymore, it's something else. For example, the Debian organization would not consider it FLOSS as it would violate the DFSG, as today.

The AGPL and GPL are about the implementation (aka the code), not data interchange formats like: APIs, network protocols, file formats.

It's worth noticing that this is no guarantee that the copyright owners will not sue you: they are always free to do so.

Answer 2

Doing this would not be a good idea as it could put your company in violation of the license. The license covers all aspects of the source code including the APIs. In addition, if you changed all the code behind the API, it could still be interpreted that the code was derived from the original code and would have to comply with the original licensing.