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JSON to TypeScript Interface Generator

Generate TypeScript interfaces from JSON instantly online. Free JSON to TypeScript converter with nested object support, array types, and proper type inference.

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TypeScript's static type system eliminates entire categories of runtime errors by catching type mismatches at compile time. When consuming a REST API or reading a JSON configuration file, developers must define TypeScript interfaces that mirror the JSON structure. Writing these interfaces by hand from a large JSON response is tedious and error-prone, especially for deeply nested objects.

TypeScript interfaces for API responses are necessary in any TypeScript or Angular project. Without them, object properties are typed as any, defeating TypeScript's purpose and suppressing IDE autocompletion. Tools like tRPC, Zod, and OpenAPI code generators all produce TypeScript types from schema definitions, but a plain JSON sample with no schema requires a different approach.

This tool parses the JSON input in the browser using JSON.parse, then recursively traverses the resulting object to infer types for each property — generating named interfaces for nested objects, union types for mixed arrays, and null unions where null values appear. No build step or npm install required.

Common Use Cases

Typing third-party REST API responses

When integrating an undocumented or poorly documented REST API (payment gateways, legacy internal services), pasting a real response payload here generates a typed interface immediately. This interface can be used as a type parameter in fetch wrappers or axios calls, enabling autocomplete and compile-time checks across the codebase.

Bootstrapping Redux state shape types

Redux Toolkit and Zustand stores require explicit TypeScript interfaces for their state slices. Pasting the initial state JSON object here produces the interface definition, which you then place alongside the slice file. This is faster than writing the interface manually and avoids property name typos between the state shape and reducer logic.

Generating types for JSON config files

Applications with complex JSON configuration files (Webpack configs exported as JSON, custom app.config.json files) benefit from TypeScript interfaces so editors can validate the config structure. Pasting the config JSON generates the interface, which can be referenced in the config-loading module to validate the parsed object at startup.

Reverse-engineering GraphQL query results

GraphQL clients like Apollo cache query results as normalized JSON. When writing a new component that reads from the Apollo cache directly (via readQuery) rather than executing a query, pasting a sample cached result here produces the TypeScript type needed for the readQuery generic parameter.

How to Use the JSON to TypeScript Generator

  1. Paste your JSON object or array in the left panel.
  2. TypeScript interfaces appear automatically in the right panel.
  3. Click "Copy Output" to copy the interfaces to your clipboard.
  4. Use "Download" to save the result as a .ts file.
  5. Use "Load Example" to see a sample with nested objects and arrays.

How Types Are Inferred