Convert any JSON object into TypeScript interfaces or type aliases instantly. Handles nested objects, arrays, optional fields, null values, and union types.
or click to browse
null values become optional and include the null type (e.g., field?: string | null). Arrays with varying object shapes are merged into a single interface covering all possible fields. Recursive structures are detected and handled safely.| null union.TypeScript has become the standard for type-safe JavaScript development. When working with external data – from REST APIs, configuration files, or databases – you often have example JSON responses but lack explicit type definitions. Manually writing interfaces is tedious and error-prone. Our JSON to TypeScript Converter automates this process: it analyzes the structure of your JSON, infers appropriate TypeScript types (string, number, boolean, null, arrays, nested objects), and generates clean, readable type definitions that integrate seamlessly into your codebase.
How the enhanced conversion algorithm works
1. Parse JSON using JSON.parse() with strict validation.
2. Recursively traverse the object with depth limit (20) and cyclic reference detection.
3. Type inference:
- Primitives → string, number, boolean, null
- Arrays → collect all element types; if objects, merge their field sets into a single interface.
- Objects → generate nested interface/type with optional marker (?) for nullable fields.
4. Proper escaping of illegal property names (e.g., "@id" → "@id").
5. Generate output with consistent indentation and export statements.
package.json, .eslintrc, or custom config files.
interface or type alias.
User, ApiResponse).
null should be marked optional (?).
.ts file.
null values become field?: type | null (when optional mode enabled) or field: type | null (required mode). This matches real-world API behavior where null is distinct from undefined.
any and a warning is shown.
@, -, . are automatically quoted.
A development team at a fintech startup was consuming a third-party payment API that returned complex JSON with nested objects and arrays. Manually writing TypeScript interfaces for every endpoint was causing delays and mismatches. By using our JSON to TypeScript converter with live API response samples, they generated accurate type definitions in seconds, reduced type-related bugs by 70%, and accelerated feature development. The ability to download the .ts file directly into their codebase streamlined CI/CD pipelines.
null, the converter produces a union with null (e.g., field?: string | null). If the “optional fields” checkbox is enabled, the field also gets a ? marker, meaning it can be omitted entirely. This matches the semantics of JSON where null is an explicit value.
name: string | number). This ensures that no data is discarded, and the resulting type is still accurate for all array elements.
any and a warning is displayed. This prevents infinite recursion and browser crashes.
@, -, or spaces) is automatically wrapped in quotes, e.g., "@id": number. This maintains valid syntax.
The converter strictly adheres to the ECMAScript JSON specification (ECMA-404) and the TypeScript Handbook for type generation rules. Our type inference logic is inspired by json2ts and quicktype, with additional enhancements for null preservation and array merging. The generated code is compatible with TypeScript 4.0+ and uses standard syntax (no experimental features).
All conversions are performed in the main thread but with safety limits to prevent UI freezes. The tool has been tested against thousands of real-world JSON samples from public APIs (GitHub, Reddit, Stripe) and internal enterprise schemas.