[pron]

> aren't all APIs simply definitions

Isn't all text simply a description of something? But what can be copyrighted isn't the something, nor is it any description, but that particular text. A REST protocol isn't a specific text while an API is.

[stdgy]

All text is a description of something, but not all text is copyrightable. I would hold that an API is a textual definition of processes used to interact with a system. I don't think that kind of rote technical description is covered by copyright.

I guess I'm confused over what you refer to when you say REST protocol. I'm imagining a textual description of endpoints, arguments and expected return types. Just technical details. Maybe you're talking about the actual implementation?

[pron]

I didn't say all text was copyrightable; I said anything that isn't text -- or any other fixed form -- isn't. A REST protocol (i.e. a REST API) doesn't have a fixed form. You can describe the very same protocol using many different texts (i.e. documentation) -- something which you cannot do for an actual API, which is text. While each of those documentation texts may be copyrightable in itself (technical documentation is very much copyrightable), the REST protocol itself isn't. It is only a mechanism, whereas an API is indeed a mechanism, but it is also a text. Since it is a text, it might be copyrightable, and since a REST protocol isn't a fixed text -- it is certainly not.