JSON to TypeScript Interface

JSON to TypeScript interface conversion is the process of analyzing a JSON object's structure and generating a corresponding TypeScript interface or type alias that describes its shape. TypeScript interfaces define the expected types of each property — string, number, boolean, array, or nested object — enabling static type checking, IDE autocompletion, and compile-time error detection. Our json to typescript interface converter automatically infers the correct TypeScript type for every JSON value, generates separate interfaces for nested objects, and handles arrays by inferring the element type from the first item.

1. 1. Paste Your JSON: Paste your JSON object into the input box. The converter accepts any valid JSON — objects, arrays, nested structures, and all primitive types. Set a custom root interface name and choose your output style (interface or type alias).
2. 2. Instant Browser-Based Conversion: Click Convert to TypeScript and the tool instantly parses your JSON, infers TypeScript types for every field, generates separate interfaces for nested objects, and produces the complete TypeScript output. All conversion runs locally in your browser.
3. 3. Copy or Download the TypeScript: Copy the generated TypeScript to clipboard or download as types.ts. Paste directly into your TypeScript project — the interfaces are ready to use with no modifications required.

• Primitive Type Inference: JSON strings map to TypeScript string, numbers to number, booleans to boolean, and null to null. The converter correctly handles all JSON primitive types including integers and floating-point numbers (both map to TypeScript number).
• Nested Object Interfaces: Nested JSON objects automatically generate separate named TypeScript interfaces. The interface name is derived from the property key in PascalCase (e.g. a "address" property generates an Address interface).
• Array Type Inference: JSON arrays generate TypeScript array types (e.g. string[], number[], Address[]). The element type is inferred from the first array item. Empty arrays generate unknown[] as a safe fallback.
• Optional Field Support: Choose "All optional" to mark every field with ? for API responses where fields may be absent. Choose "Optional when null" to only mark null-valued fields as optional. Or keep all fields required for strict type safety.

Both interface and type alias can describe object shapes in TypeScript, but they have different capabilities. interface is preferred for object types because it supports declaration merging (multiple interface declarations with the same name are merged), is more readable in error messages, and is slightly more performant in the TypeScript compiler. type alias is more flexible — it can represent union types, intersection types, and mapped types. Use interface for most API response types and data models. Use type alias when you need union types or when working with utility types like Partial<T> or Readonly<T>.