HTTP, methods, status codes, JSON and REST

Learn how programs talk over the web: a client sends a request (method + URL + headers + JSON body) and the server returns a response (status code + JSON). Methods: GET (read), POST (create / run a prediction), PUT/PATCH (update), DELETE (remove). Status codes: 200 OK, 201 created, 400 bad input, 401/403 not allowed, 404 not found, 422 invalid data, 429 too many requests, 500 server error. REST = clear URLs for resources (/predictions, /chats/{id}).