Programmatic interfaces.
WHAT AN API PROVIDES
Access to your application's functionality for other software.
WHAT TO DECIDE
What resources it exposes What each operation does What format it uses
WHAT MOST USE
JSON, over HTTP.
WHAT TO RETURN
Appropriate status codes Consistent structure Clear error messages
WHAT CONSISTENCY MEANS
The same shape for every response, including errors.
Clients depend on it.
WHAT TO DOCUMENT
Every endpoint: what it does, what it expects, what it returns, what errors are possible.
WHY
An undocumented API is unusable by anyone else.
WHAT TO IMPLEMENT
Authentication Rate limiting Validation of every input Versioning, if others depend on it
THE VERSIONING POINT
Once others use your API, changing it breaks them.
Version it before that happens.
WHAT NOT TO EXPOSE
Internal errors and tracebacks More data than the caller needs
WHAT TO LOG
Requests and failures, for diagnosis.
