Why should I use TypeScript interfaces instead of "any"?

TypeScript interfaces give you autocompletion, catch type errors at compile time, and make your code self-documenting. Using "any" defeats the purpose of TypeScript and hides bugs that would otherwise be caught before runtime.

Does the generated interface handle arrays of objects?

Yes. When the tool sees an array of objects, it creates a separate interface for the item type and uses it as the array element type (e.g., `items: Item[]`). Nested arrays are also handled recursively.

What happens with null values?

Null values produce a union type (e.g., `string | null`). If a key is null in the sample, the generated field will also be marked as optional (`?`) to reflect that the value may be absent.

Can I use the output with Zod or other validation libraries?

The output is plain TypeScript interfaces. You can use them directly for type annotations, or use a tool like json-to-zod to convert the interfaces to Zod schemas for runtime validation.

JSON to TypeScript

Generate TypeScript interfaces from JSON with nested types and optional fields

Input

Output

Shortcuts: Ctrl+Enter run · Ctrl+L clear · Ctrl+D download

About JSON to TypeScript

This tool generates TypeScript interfaces directly from a JSON sample, saving the tedious work of writing type definitions by hand. Paste any JSON object or array and get a complete, nested TypeScript interface in seconds. It detects optional fields, handles arrays of objects, and produces clean, idiomatic TypeScript that you can drop straight into your project.

✓Generates nested interfaces for deeply nested JSON structures
✓Detects optional fields when values are null or inconsistent across array items
✓Produces readable interface names derived from JSON key names
✓Handles arrays, union types, and mixed-type values automatically

From JSON Sample to Usable TypeScript

Writing TypeScript types by hand for a large API response is tedious and error-prone — it is easy to mistype a field name or miss a nested object. Generating the interface directly from a real JSON sample guarantees the type matches the actual shape of the data, at least for the sample you provide.

What a generated interface looks like

// Input JSON
{
  "id": 42,
  "name": "Alice",
  "email": null,
  "roles": ["admin", "editor"],
  "address": { "city": "Berlin", "zip": "10115" }
}

// Generated TypeScript
interface Address {
  city: string
  zip: string
}

interface Root {
  id: number
  name: string
  email: string | null
  roles: string[]
  address: Address
}

Notice that nested objects become their own named interfaces rather than being inlined — this keeps the output readable and lets you reuse the nested type elsewhere (e.g., `Address` could be reused for a `shippingAddress` field that has the same shape).

Why a generated type is a starting point, not a finished contract

·A type generated from one sample reflects only what that sample contains — if a field is sometimes present and sometimes missing, but your sample happened to include it, the generated type will incorrectly mark it as required
·Numeric fields that happen to be whole numbers in the sample (e.g., `"price": 10`) generate `number`, which is correct — but fields that are sometimes integers and sometimes decimals will only show their sampled precision
·Enums and string literal unions are not inferred — a `"status": "active"` field becomes `status: string`, even if the API only ever returns a small fixed set of values

Tip: Treat the generated interface as a first draft. Cross-reference it with API documentation (if available) to mark genuinely optional fields with `?`, narrow loose `string` fields to literal unions like `"active" | "inactive"`, and add JSDoc comments for fields whose meaning is not obvious from the name.

Interfaces vs. type aliases vs. runtime validation

·TypeScript interfaces and type aliases are compile-time only — they vanish when your code is compiled to JavaScript and provide zero protection against malformed data arriving at runtime
·If you need to guarantee that data matches a shape at runtime (e.g., validating an API response before trusting it), pair your generated types with a runtime validation library such as Zod, io-ts, or ajv with a JSON Schema
·A common pattern: generate the TypeScript interface here for editor autocompletion and compile-time checks, and generate a JSON Schema with the JSON Type Generator tool for runtime validation of the same shape