Guide · 23 July 2026
From JSON to types: stop writing them by hand
Taking an API response and re-typing its structure in your own language is the tedious job every developer knows. Here's why it pays to generate it, and how to do it well.
The problem: copying by hand
You call an API, look at the JSON that comes back, and start writing: an interface for every object, a type for every field, an array here, a nested object there. It's slow, repetitive and, above all, easy to get wrong: a field that's sometimes null, a number that occasionally arrives as a string, a property that only appears in some array elements. Every mistake becomes a bug you find at runtime.
The fix: infer the types from JSON
A type generator analyses the JSON and derives its most precise structure: it recognises numbers, strings, booleans, arrays and nested objects, and handles null values as optional fields following the chosen language's rules. Paste, pick a target and the model is ready, correct by construction. Try it with the JSON to types converter: all in the browser, the JSON never leaves your device.
JSON to TypeScript
This is the most common case: typing the result of a fetch. You can generate interface or type, or a Zod schema if you want to validate data at runtime, not just at compile time. That way the compiler warns you when you read a field that doesn't exist, instead of finding out with a production error.
JSON to Go, Rust and Python
On the backend the language changes, not the problem. From the same JSON you get Go struct with json tags, Rust structs with serde, Python classes as dataclass or Pydantic models ready for validation. It's the same model you'd write by hand, without the time and without the mistakes.
Related tools
In the same workflow you'll also want the cURL to code converter (from a command to the call in your language) and the JSON ⇄ CSV converter. They all run in the browser, sending no data.
Frequently asked questions
›Which languages can I generate from JSON?
TypeScript (interface or type), Zod, Python (dataclass or Pydantic), Go, Rust, Java, Kotlin, C#, Swift, Dart, PHP, Ruby, C++, Elixir, Haskell and JSON Schema. The same JSON becomes the right model for any backend or frontend.
›How are optional or null fields handled?
The generator infers the most precise type it can: a null value becomes an optional or nullable field following the language's conventions. If you paste an array of objects, it merges the fields of every element so properties present in only some aren't lost.
›Is my JSON sent to a server?
No. Generation happens entirely in the browser: you can paste a real API response, with sensitive data, without it leaving your device. That's why it's safer than a service that transmits the JSON to a server.