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Error responses are JSON. The body includes:
  • error — Error type name (e.g. WorkflowNotFoundError).
  • message — Human-readable description.
  • issues — (400 only) Array of validation details from the schema.
  • workflowId — (when applicable) Workflow ID tied to the error.
For 503, the server may send a Retry-After header suggesting when to retry. Workflow execution failures are different from API request errors. POST /workflow/run and GET /workflow/:id/result return the standard workflow result payload with status: "failed", output: null, and an error message. When available, that failed result also includes trace metadata. 400 ValidationError — Request body or query parameters failed schema validation (e.g. missing required fields, wrong types). The issues array lists each validation failure. 404 WorkflowNotFoundError — The given workflow execution ID does not exist, the workflow type is not in the catalog for the task queue, or the catalog workflow itself was not found. 408 WorkflowExecutionTimedOutError — Returned only by POST /workflow/run when the workflow did not complete within the request timeout (or the configured max waiting time). 424 WorkflowNotCompletedError — Returned by GET /workflow/:id/result and GET /workflow/:id/trace-log when the workflow is still running and has no final result or trace yet. 503 CatalogNotAvailableError — The catalog workflow is not reachable (e.g. worker not running or still starting). Retry after a few seconds; the response may include a Retry-After header. 500 — Unexpected server or Temporal backend error (e.g. connection failure). Check logs for details.