How to Convert JSON to TypeScript Types

Problem

You have JSON API responses and want TypeScript types to get compile-time safety and autocomplete.

Prerequisites

• Understanding of JSON
• Understanding of TypeScript types and interfaces

Steps

1. 1. Analyze the JSON structure

   The converter inspects the JSON to determine field types. Strings become string, numbers become number, booleans become boolean, null becomes null, arrays become T[], and objects become nested interfaces. Field names become property names.

   Input

   {"name":"Alice","age":30}

   Output

   types: name→string, age→number

2. 2. Generate TypeScript interfaces

   Produce interface declarations with typed properties. Nested objects become separate interfaces. Union types are generated for fields that can be multiple types. Optional properties (undefined) are marked with ?.

   Input

   JSON object

   Output

   interface MyData { name: string; age: number; }

3. 3. Refine the generated types

   Review the output and refine: use more specific types (string literals for enums, Date for date strings), rename interfaces for clarity, and add JSDoc comments. Consider making some fields optional if they are not always present in the API response.

   Input

   raw interface

   Output

   refined, documented types

Expected result

TypeScript interfaces that accurately describe the JSON structure for type-safe development.

Common errors

All fields marked as required

If some fields are optional in the API, mark them with ? in the interface. A single sample cannot determine optionality.

Date strings typed as string

JSON has no Date type. Manually change date string fields to Date or use a branded type for runtime parsing.

Troubleshooting

• If the types are too loose, add string literal types for enum-like fields.
• For arrays of mixed types, use union types or discriminated unions.

Security limits

• Type generation is a static analysis. No data is transmitted or executed.