JSON to TypeScript
Generate TypeScript interfaces from JSON instantly, in your browser.
Why use it
From JSON to type-safe interfaces in seconds
Type safety
Catch type errors at compile time, not in production. Your IDE knows the exact data structure.
Nested objects
Generates separate interfaces for each nesting level, with references between them.
Instant
Convert complex JSON structures to TypeScript interfaces in under 1 second.
Private
JSON never leaves your browser. Paste data from internal APIs with complete safety.
How it works
Three steps, no hassle
Paste your JSON
Enter the JSON object or array from which you want to generate interfaces. It can be an API response, a config file, or any data structure.
Get the TypeScript interfaces
The generator analyzes the structure, detects nested objects, arrays, and primitive types, and produces TypeScript interfaces with descriptive names.
Copy and use in your project
Copy the generated interfaces and paste them into your TypeScript code. Get autocomplete and type safety from first use.
FAQ
Got questions?
TypeScript provides compile-time type safety, meaning type errors are caught before code runs. When working with REST APIs, data arrives as JSON with no type information. Generating TypeScript interfaces from the API response gives you IDE autocomplete, compile-time error detection, and implicit documentation of the data structure, reducing production bugs.
Nested objects are converted into separate interfaces that reference each other. For example, if you have a User object with an address property that is another object, the generator creates an Address interface and a User interface where address: Address. This keeps the code organized and reusable.
By default, all JSON fields are generated as required. If a field can be null or undefined in the real API, you must manually mark it as optional by adding ? after the name (field?: type) or adding null to the type (field: string | null). Some generators infer optionality if the field appears absent across multiple examples of the same structure.
If an array contains elements of different types (e.g. [1, 'text', true]), TypeScript generates a union type: Array<number | string | boolean>. If all elements are the same type, it generates the specific type: number[]. For arrays of objects, it generates an interface for the object and uses Array<InterfaceName>.
JSON Schema is a runtime data validation standard, language-agnostic, defined by the IETF (draft-07 and above). TypeScript interfaces are compile-time constructs that only exist in source code and disappear after transpilation to JavaScript. JSON Schema validates real data in production; TypeScript interfaces only validate during development. You can use both: interfaces for the IDE and JSON Schema for input validation on the server.
TypeScript: history, structural typing, and why it changed web development
TypeScript was created by Anders Hejlsberg at Microsoft and publicly announced in October 2012 (version 0.8). Hejlsberg is also the creator of Turbo Pascal (1983) and lead architect of C# (2000), two languages that defined eras in the industry. TypeScript's motivation came from the problems of scaling large JavaScript applications: without static types, errors are only discovered at runtime, refactoring is dangerous, and IDE autocomplete is limited. The first public version of TypeScript compiled to JavaScript ES3 and ES5.
TypeScript's type system uses structural typing (duck typing), unlike languages like Java or C# which use nominal typing. In structural typing, two types are compatible if they have the same shape, regardless of their name or declaration. This means that if a function expects an object with {name: string, age: number}, any object with those properties is accepted, even if it doesn't explicitly declare implementing any interface. This design choice makes TypeScript more natural for working with JSON and JavaScript objects.
TypeScript adoption has been meteoric: in the State of JS 2024 survey, over 78% of JavaScript developers use it regularly. Tools like quicktype.io (open source, available as CLI and library) and json2ts.com popularized automatic TypeScript interface generation from JSON. In the modern API-first workflow, it is common to generate TypeScript interfaces directly from OpenAPI/Swagger specifications using tools like openapi-typescript, ensuring the TypeScript client is always synchronized with the server specification.