HTTP Status Codes

HTTP status codes are three-digit numbers returned in every API response to indicate the outcome of the request. They are grouped into classes: 2xx (success), 4xx (client errors), and 5xx (server errors).

The most important codes for API integrations: 200 (success), 400 (bad request - check parameters), 401 (unauthorized - check API key), 404 (not found), 429 (rate limit exceeded), and 500 (server error).

Robust API integrations check status codes on every response rather than assuming success. Handling 429 with retry logic, surfacing 401 as a misconfiguration, and logging 500 errors for investigation are the building blocks of a resilient API client.