Worked on enhancing the Permit Service API contract in the UKHO/s-100-permit-service repository, focusing on improving integration reliability and error handling. Refactored the OpenAPI Specification by migrating response definitions to component references and introducing a 429 Too Many Requests response, which clarified contract expectations and supported client resilience. Improved error messaging by refining descriptions for BadRequest and TooManyRequests scenarios, reducing ambiguity for API consumers. Documented the use of the origin header with explicit examples and ensured its consistent presence across all responses. Utilized YAML and OpenAPI Specification skills to streamline documentation, increase maintainability, and lay the foundation for future API resilience.