API errors use application/problem+json: type, title, status, code and requestId. detail is included only where useful without revealing internals. traceId connects the error to tracing.
400 validation_failed / validation_error / invalid_request: fix the input. 401 invalid_credential / authentication_required: renew valid credentials. 403 insufficient_scope: missing scope or an application key used on a human endpoint.
404 resource_not_found: missing or unowned resource. 409 conflict / concurrency_conflict: check current state. 428 precondition_required: send If-Match. 429 rate_limit_exceeded: honor Retry-After. 503 service_unavailable / search_unavailable: temporarily unavailable.
Previously published catalog type URIs api.aniyori.cz/problems/* are retained. New types use docs.aniyori.cz/errors/*. Branch programmatically on code.
X-Request-Id is generated by the server. Share the ID when reporting an issue, never a token or key.