Standard HTTP status codes with a consistent JSON envelope.

{ "error": { "code": "rate_limit_exceeded", "message": "Too many requests", "retry_after": 30 } }

Common codes

• 400 — malformed request
• 401 — missing or invalid key
• 402 — quota exhausted (upgrade your plan)
• 404 — resource not found
• 429 — rate limited (see Retry-After)
• 5xx — transient server error, retry with backoff