Working on your organisations API design guidelines ? Here is a reference.

The API Stylebook http://apistylebook.com  provides API designers with a curated list of publicly available API design guidelines (style guides). The guidelines are categorised by design topics making it easy to see what the approach taking by different API design guidelines on a specific topic. For example, Naming.

Any working on API design guidelines and governance can use this as a handy resource to draw inspiration from existing guidelines. The API Stylebook was created and is maintained by Arnaud Lauret. 

Apart from this, I also like the

• REST style guide published by the Belgian government.
• Zalando API Style Guide
• Haufe-Lexware API Style Guide