Errors

Errors use application/problem+json. Branch on the stable code field rather than matching the human-readable message.

{
  "type": "https://semantil.com/problems/invalid-api-key",
  "title": "Invalid API key",
  "status": 401,
  "code": "invalid_api_key"
}

Practical handling

Status	What to do
400	Fix the request; retrying unchanged will not help.
401	Check or replace the API key.
403	Use a key with access to the requested action.
429	Respect Retry-After, then retry with backoff.
5xx	Retry idempotent requests with exponential backoff and jitter.

The live GET /api/errors endpoint lists the current problem codes without requiring an API key.