How to Build Custom GPT Actions with OpenAPI

Build Custom GPT Actions with OpenAPI

Custom GPTs use OpenAPI 3.1 schemas to call your API. Get the schema wrong and the GPT silently refuses to call your endpoint.

The essentials

• servers[0].url must be HTTPS
• Each operation needs an operationId and summary
• Auth goes in components.securitySchemes
• No unions in request bodies — flatten them

Generate one in seconds

Our GPT Connector turns a plain-English API description into a valid OpenAPI 3.1 schema you can paste directly into a Custom GPT.