Protocols are the how around the endpoints: how to read, how to write, how to authenticate, how to subscribe, how to treat an error, how to test. They sit between api (the paths) and patterns (caching, retries, pagination).
Query protocol is reads. Action protocol is writes — sequence numbers, gas, the -- rule. Authentication covers keys, addresses, and webapp sessions. Streaming is GRASS over NATS. Error handling is what to do when the string you got is not in the happy-path example.
Gameplay and economic protocols describe longer loops (mine-refine, agreements) as protocols rather than as a single POST. Testing protocol is how to exercise an integration without burning a live sequence on guesswork. Prefer a local devnet for first attempts.
Open protocols when you are implementing a client or a test harness. If you are playing with structsd, the conventions skill already has the flags you need. Come here when you are about to wrap those flags in your own code.