JSON → TypeScript
Interface Generator

About JSON to TypeScript Interface Generator

This free online JSON to TypeScript converter tool allows you to transform JSON data into accurate, ready-to-use TypeScript interfaces and vice versa. Whether you're a developer working with APIs, defining type contracts, or generating mock data from type definitions, our bidirectional converter intelligently infers types (string, number, boolean, Date, arrays, nested objects), detects optional fields, handles union types, and creates production-ready TypeScript interfaces. Everything runs 100% in your browser with no server uploads.

Why Convert Between JSON and TypeScript?

TypeScript's type system is essential for modern web development, providing compile-time type safety and better IDE autocomplete. However, manually writing TypeScript interfaces from API responses, database records, or JSON configuration files is tedious, time-consuming, and error-prone. Automated JSON to TypeScript conversion eliminates manual typing errors, ensures type accuracy, speeds up development by generating interfaces instantly, maintains consistency between data shapes and type definitions, and helps document API contracts. Reverse conversion (TypeScript to JSON) generates mock data templates, creates test fixtures, documents expected data structures, and provides examples for API documentation.

How to Use This Converter

Choose your conversion direction: JSON → TypeScript mode analyzes your JSON data (object or array), infers field types (string, number, boolean, Date for ISO strings, arrays, nested objects), detects optional fields (marked with ?) when keys are missing or null in array elements, handles union types for mixed values, and generates clean TypeScript interface definitions ready to paste into your code. TypeScript → JSON mode parses interface definitions and creates matching JSON skeletons with placeholder values for testing or documentation. Paste your data, click Generate Interface or Convert to JSON, and get instant results ready to use in your TypeScript project.

Key Benefits

• No installation required: Works directly in your browser without any software downloads
• Completely free: No registration, credit card, or hidden fees
• Secure and private: All conversion happens locally - your data never reaches our servers
• Fast processing: Instant interface generation with no waiting time
• Bidirectional: Convert JSON ↔ TypeScript interfaces with full roundtrip support
• Smart type inference: Automatically detects string, number, boolean, Date, arrays, objects
• Optional field detection: Keys missing in some array elements become optional (?)
• Nested structure support: Handles deeply nested objects and arrays correctly

Common Use Cases

Developers use JSON to TypeScript converters for generating interfaces from API responses instantly instead of manual typing, creating type definitions for third-party API integrations, defining types for database query results and ORM models, converting JSON configuration files to typed interfaces for better IDE support, generating TypeScript types from GraphQL query results, creating mock data types for testing and development, documenting API contracts with accurate type definitions. Frontend engineers type Redux state, API payloads, and component props from sample data. Backend developers generate types for request/response bodies, database schemas, and microservice contracts. Full-stack teams maintain type safety between frontend and backend by generating shared interfaces from JSON examples.

Supported TypeScript Features

JSON to TypeScript conversion generates proper interface definitions with accurate type inference: strings become string type, numbers map to number, booleans to boolean, ISO date strings (YYYY-MM-DD, ISO 8601) convert to Date, null values result in optional fields with ?, arrays generate proper array syntax (Type[] or Array<Type>), nested objects create separate interfaces with proper references, mixed-type arrays produce union types (string | number), and objects with varying structures generate union types or discriminated unions. TypeScript to JSON parsing extracts interface names, field types, optional modifiers, array types, nested interfaces, and generates matching JSON with appropriate placeholder values (empty strings for string, 0 for number, false for boolean, ISO date string for Date, empty arrays/objects for complex types).

Technical Features

The converter intelligently analyzes JSON structure and applies TypeScript best practices: generates clean, readable interface definitions with proper indentation, names interfaces based on context (RootObject, ItemType, etc.), handles edge cases like empty arrays, null values, and undefined, supports deeply nested structures with multiple levels, detects and creates union types for heterogeneous data, preserves field order from original JSON, generates proper export statements for module usage, and includes JSDoc comments for complex types. Error messages help debug invalid JSON or TypeScript syntax. Quick actions include copy to clipboard, download (.ts or .json files), and swap for roundtrip conversion testing.

Privacy and Security

Unlike online converters that upload your data to remote servers, this tool processes everything locally in your browser using JavaScript. Your API responses, database records, user data, configuration files, or any sensitive JSON structures never leave your computer, making it completely safe for converting production data and confidential API contracts. No cookies, tracking, data storage, or server communication. Perfect for working with proprietary API schemas, internal service contracts, customer data structures, financial records, healthcare data, or any sensitive information that requires strict privacy controls. Your TypeScript code and data shapes remain secure.