Google shared its API Design Guide with the community and it has been added to the API Stylebook.
This is a general design guide for networked APIs. It has been used inside Google since 2014 and is the guide we follow when designing Cloud APIs and other Google APIs. It is shared here to inform outside developers and to make it easier for us all to work together.
This guide applies to both REST APIs and RPC APIs, with specific focus on gRPC APIs. gRPC APIs use Protocol Buffers to define their API surface and API Service Configuration to configure their API services, including HTTP mapping, logging, and monitoring.
The documentation section is really interesting giving guidelines on how to write your API (technical) documentation. If you remember only one thing concerning documentation, let it be this quote:
In most cases, there’s more to say than just restating the obvious
Versioning and how to determine if a change is a breaking one or not are very well explained (see Versionning).
To have a quick look at all the topics covered by the Google API Design Guide, click here..