JSON to Types

What is JSON to Types?

JSON to Types turns a JSON example — typically an API response — into strongly-typed source code in the language you're working in: TypeScript interfaces, Go structs with the right json: tags, Python Pydantic BaseModel classes, Rust serde-derived structs, or plain Java classes ready for Jackson. It infers the shape recursively, deduplicates identical sub-objects into shared types, marks fields optional when they're missing from some array elements, and produces output you can drop straight into your project.

What it generates

• Type-correct primitives — integers, floats, booleans, strings, and null map to each language's idiomatic type (number, int64, i64, Long, etc.).
• Optional fields — when an array of objects has the same key sometimes missing, the field is marked optional (?, pointer in Go, Option<T> in Rust, default-None in Pydantic).
• Nested types are extracted into named structs/classes and reused if their shape repeats.
• Heterogeneous arrays become union types in TS and string + comment in stricter languages.
• Snake-case ↔ camel-case conversion of field names, with the original name preserved in the JSON tag / alias so on-the-wire data still round-trips.

Why it's better than copy-pasting

Most "JSON to TypeScript" web tools handle one language. Most CLI tools (quicktype, gojson) require an install and a mental tax to remember their flags. This tool runs in the browser, supports five mainstream languages from one input, and lets you tweak the root name, naming convention, and optional-field strategy without leaving the page. Your JSON never leaves your device — paste real production samples without worrying about a third-party server logging them.

Tips

• For arrays, paste an array of representative objects (3–10 items) so the tool can detect optional fields correctly.
• If you see a field typed as any / interface{} / Box<dyn Any>, the corresponding JSON value was either null in every sample or an empty array — provide a non-empty example to narrow it.
• Use the Optional dropdown to switch between foo?: T and foo: T | null styles depending on your codebase's convention.