JSON to TypeScript Converter
Convert JSON data to TypeScript interfaces instantly. Paste your JSON below to generate type-safe TypeScript definitions.
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JSON Input
TypeScript Output
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How to Use the JSON to TypeScript Converter
This free online JSON to TypeScript converter is the fastest way to generate type-safe TypeScript interfaces from any JSON data. Simply paste your JSON into the input area on the left, and the corresponding TypeScript interfaces appear instantly on the right. The tool analyzes every property, detects types, and generates clean, properly formatted TypeScript code that you can copy directly into your project.
The converter handles complex JSON structures including deeply nested objects, arrays of objects, mixed-type arrays, and null values. Each nested object is extracted into its own named interface using PascalCase naming derived from the property key. For example, a property called "shipping_address" generates a ShippingAddress interface. Arrays are analyzed to determine their element type, and if an array contains objects, a separate interface is generated for the element shape.
Use the options panel to customize the output to match your project's coding style. Toggle between interface and type declarations depending on whether you prefer extendable interfaces or flexible type aliases. Enable optional properties to add ? to every property, which is useful when working with partial API responses. The readonly option marks all properties as immutable, and the export toggle adds the export keyword for use in modular TypeScript projects.
Why TypeScript Types Matter
TypeScript's type system catches errors at compile time rather than runtime. When you define interfaces for your API responses, configuration objects, and data models, your editor provides autocompletion, inline documentation, and immediate feedback when you access a property that doesn't exist. This reduces bugs, speeds up development, and makes refactoring safer across large codebases.
Manually writing TypeScript interfaces from JSON is tedious and error-prone, especially for large or deeply nested data structures. This converter automates that process entirely. Whether you're integrating a third-party REST API, defining types for your database models, or converting mock data into proper type definitions, the tool saves you significant time and ensures accuracy.
Type Inference Rules
The converter uses the following rules to infer TypeScript types from JSON values: string values map to string, numbers (both integers and floats) map to number, booleans map to boolean, and null values map to null. Nested objects generate separate named interfaces. Arrays of a single type produce Type[], while arrays containing multiple types produce union arrays like (string | number)[]. Arrays of objects merge all elements into a single interface that covers all observed properties.
All processing runs entirely in your browser. No data is transmitted to any server, making the tool safe for sensitive payloads. The one-click copy button lets you grab the generated TypeScript code and paste it directly into your editor, and the share button creates a URL that encodes your current settings for easy sharing with teammates.
Frequently Asked Questions
How does JSON to TypeScript conversion work?
The converter analyzes your JSON data structure and infers TypeScript types for each property. It examines values to determine whether they are strings, numbers, booleans, arrays, or nested objects, then generates corresponding TypeScript interfaces with proper type annotations. Nested objects become separate named interfaces, and arrays are typed based on their element types.
Can it handle nested objects and arrays?
Yes. Nested objects are extracted into their own named interfaces using PascalCase derived from the property key. Arrays are analyzed to determine their element type. If an array contains objects, a separate interface is generated for the element type. Mixed-type arrays produce union types like (string | number)[].
What is the difference between interface and type in TypeScript?
Both define the shape of an object, but interfaces are extendable via declaration merging and the extends keyword, making them ideal for object shapes and API contracts. Type aliases are more flexible and can represent unions, intersections, and primitives. For most JSON-to-TypeScript use cases, interfaces are preferred because they are easier to extend and produce clearer error messages.
How are null values handled in the generated TypeScript?
When a JSON property has a null value, the converter types it as null since the actual type cannot be inferred from the data alone. This produces properties like 'metadata: null'. If you know the intended type, you can manually adjust it to something like 'metadata: Record<string, unknown> | null' after conversion.
Is my JSON data secure when using this tool?
Absolutely. All conversion happens entirely in your browser using client-side JavaScript. Your JSON data is never sent to any server. This makes it safe for converting sensitive API responses, configuration files, and private data structures.
Can I use the generated types directly in my TypeScript project?
Yes. The generated interfaces are valid TypeScript that you can copy directly into a .ts or .d.ts file in your project. Enable the 'Export interfaces' option to add the export keyword, making them ready for import in other modules. You may want to review and adjust the root interface name, optional properties, and null types to match your specific requirements.