What's the output shape?

TypeScript interface and type alias definitions. Each nested JSON object becomes its own interface; arrays become `Type[]` with the inferred element type.

How does it detect optional fields?

Fields present in every sample record are required. Fields missing from any record get the `?` optional marker. Small samples may misclassify — review the output.

Does it handle unions?

Mixed-type values (sometimes string, sometimes number) become union types. `string | number` is common; more complex unions (discriminated) need manual cleanup.

Interface or type alias?

Both supported — toggle the output preference. Interfaces allow declaration merging; type aliases allow unions and mapped types. Pick per project convention.

JSON → TypeScript Types

DevTools Surf

Example: JSON → TypeScript Types

A worked example, rendered from real sample data. Sign in to run the tool on your own input.

Input

{"id":42,"name":"Ada Lovelace","email":"ada@example.com","active":true,"tags":["admin","early-adopter"],"profile":{"age":36,"city":"London"}}

Output

export interface Root {
  id: number;
  name: string;
  email: string;
  active: boolean;
  tags: string[];
  profile: {
    age: number;
    city: string;
  };
}

About JSON → TypeScript Types

JSON → TypeScript Types preview - Converters tool

Infer TypeScript interfaces from JSON with deep nesting + optionals. Part of the DevTools Surf developer suite. Browse more tools in the Converters collection.

Use Cases

Generate TypeScript types from a live API response
Bootstrap a SDK from example payloads
Add typing to legacy endpoints without hand-writing interfaces
Convert webhook payload samples into strong-typed handler signatures

Tips

The output is a single root interface; nested objects become inline types
Union types are inferred from arrays of mixed elements
null fields are marked optional with the ? modifier

Fun Facts

TypeScript 4.1 added template-literal types, which let you derive string types from other string types at compile time.
TypeScript's type system is Turing complete — you can implement a full calculator or even a chess engine entirely within the type system.
Anders Hejlsberg, creator of TypeScript, also created Turbo Pascal, Delphi, and C# — four of the most influential programming languages in history.

FAQ

What's the output shape?: TypeScript interface and type alias definitions. Each nested JSON object becomes its own interface; arrays become `Type[]` with the inferred element type.
How does it detect optional fields?: Fields present in every sample record are required. Fields missing from any record get the `?` optional marker. Small samples may misclassify — review the output.
Does it handle unions?: Mixed-type values (sometimes string, sometimes number) become union types. `string | number` is common; more complex unions (discriminated) need manual cleanup.
Interface or type alias?: Both supported — toggle the output preference. Interfaces allow declaration merging; type aliases allow unions and mapped types. Pick per project convention.

Related Converters Tools

JSON to XML JSON to CSV JSON to YAML JSON to TSV JSON to String XML to JSON XML to CSV XML to String