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JSON to TypeScript Converter (Free AI Tool)
Convert JSON to TypeScript interfaces instantly with intelligent type inference. Generate type-safe interfaces from API responses with automatic detection of optional properties, union types, and nested structures. Eliminate manual interface writing and catch type errors at compile time.
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Hint: Select conversion type, paste your data, and get instant conversion. Supports JSON, YAML, XML, Excel, PDF, and more.
How It Works
- 1
Paste JSON API Response or Data Object
Input your JSON from REST APIs, GraphQL responses, configuration files, or database exports. Paste multiple objects to improve optional property detection accuracy.
- 2
AI Infers Types, Optionals, and Union Types
The AI analyzes property types (string, number, boolean, object, array), detects optional fields with ? syntax, generates union types for nullable values (string | null), and creates nested interfaces for complex objects.
- 3
Copy Production-Ready TypeScript Interfaces
Receive TypeScript interface definitions with export keywords, PascalCase naming, nested interfaces for sub-objects, and array type annotations. Ready to paste into your .ts files for immediate type safety.
JSON vs TypeScript: Type Safety Comparison
| Feature | JSON (Plain) | TypeScript Interface |
|---|---|---|
| Type Safety | None (runtime only) | Compile-time type checking |
| Property Access | Any property, no errors | Autocomplete + error on typos |
| Refactoring | Manual search/replace | IDE-assisted refactoring |
| Documentation | Separate docs or comments | Self-documenting types |
| Nullable Handling | Manual null checks | Optional chaining + union types |
| API Contract | Implicit assumptions | Explicit interface contract |
Code Examples
Example 1: Simple API Response to Interface
{
"id": 123,
"name": "John Doe",
"email": "[email protected]",
"isActive": true,
"lastLogin": null,
"roles": ["admin", "user"]
}export interface User {
id: number;
name: string;
email: string;
isActive: boolean;
lastLogin: string | null;
roles: string[];
}Key Changes:
The converter infers primitive types (number, string, boolean) from JSON values. The null value for lastLogin generates a union type (string | null) to handle both present and absent cases. The roles array becomes string[] indicating an array of strings. The interface is automatically exported for use across modules.
Example 2: Nested Objects with Optional Properties
{
"user": {
"id": 1,
"profile": {
"firstName": "Jane",
"lastName": "Smith",
"age": 30
},
"settings": {
"theme": "dark",
"notifications": true
}
},
"timestamp": 1234567890
}export interface Profile {
firstName: string;
lastName: string;
age: number;
}
export interface Settings {
theme: string;
notifications: boolean;
}
export interface User {
id: number;
profile: Profile;
settings: Settings;
}
export interface RootObject {
user: User;
timestamp: number;
}Key Changes:
Nested JSON objects automatically generate separate TypeScript interfaces with meaningful names derived from property keys. The Profile, Settings, and User interfaces are extracted and referenced by type. This modular approach allows interface reuse across your codebase. Each level of nesting becomes its own interface definition, making the type structure clear and maintainable.
Frequently Asked Questions
The converter analyzes your JSON sample and infers optional properties using the ? syntax for fields that appear inconsistently across objects. Null values generate union types (string | null). If multiple samples show different presence patterns, properties are marked optional. Arrays with mixed types become union arrays (e.g., (string | number)[]).
No. All JSON to TypeScript conversion happens client-side in your browser using JavaScript-based type inference. Your JSON data—whether API responses, database exports, or configuration files—never leaves your machine. The tool works offline once loaded.
The converter handles nested objects, arrays, and mixed types with 95%+ accuracy. However, single JSON samples may not represent all runtime variations. For production use, review generated interfaces against multiple API response examples. Union types for enum-like values require manual refinement to literal types if you want strict enums.