MUST

MUST use problem json for errors

The content type for 4xx and 5xx status codes MUST be application/problem+json.

For OpenAPI definitions marked with info.x-api-type: pygeoapi, the paired -pygeoapi sibling rule fires at warn instead. See 1.

Invalid Example

The content type for the 503 response in this example incorrectly uses the application/json content type.

responses:
   '503':
     description: ...
     content:
       application/json:
         schema:
           $ref: ../models/Problem.yaml

Valid Example

The content type for the 503 response in this example correctly uses the application/problem+json content type.

responses:
   '503':
     description: ...
     content:
       application/problem+json:
         schema:
           $ref: ../models/Problem.yaml

Zalando Guideline 176

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Published: 24 January 2025
Last updated: 2 July 2026
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