JSON to TypeScript

How JSON to TypeScript works

Turn a JSON sample into TypeScript interfaces automatically. Nested objects become their own interface, and arrays become typed arrays. Everything happens inside this page: the tool reads your input, runs the calculation or conversion locally, and hands the result back to you. Nothing is transmitted, because there is no backend to transmit it to.

That design choice is deliberate. Most free tool sites upload your files to a server, process them there, and quietly keep a copy. Toolcin cannot do that — the site is a set of static files. If your connection dropped the moment the page finished loading, every tool would still work.

Interfaces from a sample

Paste a JSON sample and the tool writes TypeScript interfaces. Top-level keys become properties, nested objects become their own named interface, and an array of objects becomes an array of that interface type.

The root interface name is configurable, which matters because the name ends up in every import that uses it.

The inference is only as good as the sample

Every type is inferred from one value. If the sample has age: 30, the type is number — and a later response with age: null or a string will not compile. Union types and optionals cannot be discovered from a single example.

The practical habit: take the largest, most varied response you have, convert that, then hand-edit the optional fields. Generated interfaces are a starting point that saves typing, not a contract.

Naming and structure

Nested objects are named from their key, capitalised — a user object becomes User. Arrays of primitives become string[] or number[] rather than a named type.

Keys that are not valid identifiers, such as kebab-case or names with spaces, need quoting in the output; check those before trusting the file to compile.

Good to know

• Works offline once loaded, including on flights and in locked-down networks.
• No file size limit beyond your device's own memory.
• Free to use, with no account and no usage counter.
• Results are produced locally, so they are not logged or shared with anyone.

Questions