How to Generate TypeScript Types from JSON API Responses
Use sample API responses to draft TypeScript interfaces, then refine them into reliable application contracts.
A JSON response tells you what an API returned once; a TypeScript type explains what your application expects every time. Turning a representative response into an interface is a fast way to replace repeated property guessing with editor hints and safer refactors.
Begin with a realistic successful response that includes optional-looking fields and nested objects. A tiny happy-path sample can produce a type that is too narrow, while an accidentally mixed sample can hide which fields are genuinely optional.
Paste the sample into /tools/json-to-typescript to get a starting interface, then review each inferred property. Rename the root type to match your domain, replace vague fields with meaningful unions where appropriate, and model arrays based on the values your API actually guarantees.
Generated types do not validate data at runtime. Network responses can still be malformed, outdated, or affected by a backend rollout, so use schema validation or careful guards at boundaries where untrusted data enters the application.
Avoid copying generated output without ownership. Keep API types near the client that uses them, document non-obvious fields, and update samples when the API contract changes so the type remains a useful description rather than an optimistic snapshot.