How to turn an OpenAPI spec into a ChatGPT app

Import a supported OpenAPI operation, review its tool contract and build a ChatGPT app draft. Learn the requirements, testing steps and common blockers.

Start with one useful API operation

An OpenAPI specification describes an HTTP API. A ChatGPT app needs a smaller, usable contract: a named tool, its inputs and the result people can understand. DraftYourApp lets you inspect a local document and turn one supported operation into a draft before designing the interface.

For a first project, choose a public product lookup or service-status endpoint. Define a concrete question such as “What is the status of request 1042?” Keep the first draft to one operation so you can check its parameters and response independently.

Which OpenAPI specifications can you import?

• OpenAPI 3.0 or 3.1 in JSON, pasted or uploaded, up to 512 KiB.
• Local schema references and an absolute public HTTPS server URL without URL credentials, query strings, fragments or server templates.
• A public GET operation without authentication requirements, scalar path/query parameters and a supported JSON success-response schema.

Inspection lists incompatible operations with diagnostics. An authenticated endpoint, a write operation or an unsupported response may appear in the document without being eligible for draft creation. This flow is deliberately narrower than a universal API converter.

Inspect, test and review before creating a draft

• Start a new project using the OpenAPI path and paste or upload your JSON document. Inspection does not call the API server.
• Select a supported operation. Check the proposed tool name, HTTP method, destination, parameters and response shape.
• Run the explicit operation test with representative input when you are ready to contact the API. Review the result and any diagnostic before continuing.
• Confirm the reviewed proposal to create the draft, then open it in the visual editor.

The draft retains source provenance so the selected operation can be reviewed later. Imported source metadata is not a replacement for testing the deployed tool or checking the upstream service’s availability.

Design a response that answers the user’s question

For a product lookup, display the name, availability and one useful next action. For a status lookup, show the status and a meaningful timestamp when the response provides it. Avoid adding a field simply because it exists in the API.

Use the editor’s component library and local conversation preview to check hierarchy, empty results and parameter mapping. Simulated actions help inspect the interface without calling your API; a passing preview does not demonstrate a successful remote request.

Common import blockers and what to do next

• Authentication required: use a supported connection workflow rather than removing security from a private API.
• Remote references: produce a document with local references; inspection does not fetch external schema URLs.
• Unsupported parameters or responses: isolate a simpler public GET operation or revise the upstream contract.
• Unexpected test output: check the selected server, parameter values and success-response schema before creating another draft.

If you already maintain an MCP server, inspect its original tool contracts instead of translating them back into OpenAPI. Deployment and ChatGPT host testing come after the draft review.