JSON to TypeScript Interface

A TypeScript interface is a way to define the shape of an object in TypeScript. It specifies the names and types of properties that an object should have, enabling compile-time type checking and better IDE autocompletion.

The tool parses your JSON input and recursively analyzes each value to infer the appropriate TypeScript type. Objects become interfaces, arrays become typed arrays, and primitive values map to their TypeScript equivalents (string, number, boolean, null). Nested objects generate additional interfaces.

No. All processing happens entirely in your browser using JavaScript. Your JSON data is never transmitted to any server, so sensitive data remains completely private.

When optional fields mode is enabled, all fields in the generated interface are marked with "?" to indicate they are optional. This is useful when working with APIs that may not always return all fields. When disabled, all fields are required.

Arrays are typed based on the types of their elements. For example, an array of strings becomes string[], an array of numbers becomes number[], and an array of objects generates a separate interface and uses that interface type for the array.

JSON null values are typed as "null" in the generated TypeScript. If a field could be either a value or null, you may want to manually adjust the type to something like "string | null" to properly reflect the field's possible values.

Yes. The tool recursively processes nested objects and generates separate TypeScript interfaces for each nested object level. Each nested object gets its own named interface, keeping the output clean and readable.

The root interface is always named "Root" by default (customizable). Nested objects generate interfaces with PascalCase names derived from their property keys — for example, a property named "userProfile" generates an interface called "UserProfile".

The tool supports all common JSON types: string, number, boolean, null, arrays, and objects. Mixed-type arrays (where elements have different types) generate union types like "(string | number)[]".

Yes. The generated interfaces are valid TypeScript and can be copied directly into your project. You may want to rename "Root" to a more meaningful name and adjust optional/required fields based on your actual API contract.

If the JSON input is invalid, the tool will display an error message indicating what went wrong. Common issues include missing commas, unquoted keys, or trailing commas. You can use the JSON Formatter tool to validate and fix your JSON first.

The tool generates concrete interfaces based on the actual JSON structure without generics. For more complex type scenarios involving generics or conditional types, you will need to manually adjust the generated output.