JSON to TypeScript is a powerful developer tool that automatically generates TypeScript interface definitions from JSON data. TypeScript's static typing system helps catch errors at compile time and provides excellent IDE support with autocompletion and inline documentation. However, manually writing type definitions for complex JSON structures is tedious and error-prone. This tool analyzes your JSON data structure and produces clean, accurate TypeScript interfaces that you can copy directly into your codebase. Whether you are working with API responses, configuration files, database records, or any other JSON data, this converter handles nested objects, arrays, primitive types, and null values intelligently. The generated code follows TypeScript best practices, making it immediately usable in production codebases. All processing happens in your browser, so sensitive data never leaves your machine.
How to use this JSON to TypeScript converter?
Paste your JSON data in the left input panel. The tool instantly parses the structure and generates corresponding TypeScript interfaces in the right panel. You can customize the root interface name using the input field at the top, which is helpful when generating types for specific API endpoints or data models. The output updates in real time as you modify the JSON, letting you experiment with different structures quickly. Once satisfied, use the copy button to transfer the generated types to your clipboard. For arrays, the tool infers the element type by analyzing all items and creates appropriate union types when elements have different structures.
Why generate TypeScript types from JSON?
TypeScript provides compile-time type checking that catches many bugs before they reach production. When working with external APIs or JSON data, having accurate type definitions enables IDE features like autocompletion, inline documentation, and refactoring support. Manually typing complex nested structures is time-consuming and prone to mistakes, especially when APIs evolve frequently. This tool automates the process, ensuring your types always match the actual data structure. It is particularly valuable during initial development when integrating new APIs, or when updating types after API changes. The generated interfaces serve as documentation, making it easier for team members to understand data shapes without checking external documentation.
Type inference rules
- Objects are converted to interfaces with typed properties.
- Arrays infer element types from all items, using union types when needed.
- Primitive types (string, number, boolean) are directly mapped.
- Null values generate nullable types for flexibility.
- Nested objects create inline type definitions.
- Empty arrays default to unknown[] since element type cannot be inferred.
- Special characters in keys are quoted to ensure valid TypeScript syntax.
Best practices for using generated types
Start with representative sample data that covers all possible fields and edge cases. API responses sometimes omit optional fields, so use complete examples to generate accurate types. Review generated types for optionality, as fields present in all samples might still be optional in the actual API. Consider extracting nested interfaces into separate named types for better reusability. Add JSDoc comments to document field purposes. When APIs return different shapes based on parameters, generate types for each variant and use discriminated unions. Regularly regenerate types when APIs update to keep your codebase in sync with backend changes.
Integration with TypeScript projects
Copy generated interfaces into a dedicated types file (e.g., types/api.ts) to keep type definitions organized. Import these types where needed to annotate function parameters, return values, and variables. For API clients, use the generated types with fetch wrappers or libraries like axios to get full type safety on request and response data. When using state management libraries like Redux or Zustand, generated types help ensure store shapes match expected data. In React projects, typed props improve component contracts and enable better refactoring. The generated code is framework-agnostic, working equally well in Node.js backends, frontend apps, and full-stack projects.
FAQ
Q: Should I use interface or type for generated definitions?
A: This tool generates interfaces for object types, which is generally preferred in TypeScript. Interfaces can be extended and merged, making them more flexible for evolving APIs. However, both work similarly for most use cases. If you prefer type aliases, you can easily convert the generated interface to a type by changing 'interface Name' to 'type Name ='.
Q: How does the tool handle arrays with mixed types?
A: When array elements have different structures, the tool creates a union type covering all variants. For example, an array containing both strings and numbers becomes (string | number)[]. For objects with varying shapes, the union includes all distinct object types. This ensures the generated type accepts all values present in your sample data.
Q: Can I generate types for deeply nested JSON?
A: Yes, the tool recursively processes nested objects to any depth. Each nested object generates an inline type definition within its parent. For very deep structures, consider extracting frequently used nested types into separate named interfaces after generation for better readability and reuse.
Q: How do I handle optional fields?
A: The tool generates required properties based on the sample data. If a field might be absent in some responses, manually add the optional modifier (?) after the property name in your generated type. Alternatively, provide sample data that includes null values for optional fields, and the tool will generate nullable types.
Q: Is my JSON data secure?
A: Yes, all processing happens locally in your browser. Your JSON data is never sent to any server. You can verify this by using browser developer tools to monitor network activity, or by disconnecting from the internet and confirming the tool still works. This makes it safe to convert sensitive configuration data or proprietary API responses.