JSON to TypeScript Model Generator

JSON to TypeScript Model Generator

The JSON to TypeScript Model Generator converts JSON into strongly typed TypeScript interfaces so you can build safer front-end and Node.js applications. Instead of manually writing interfaces, paste a sample JSON payload and generate accurate TypeScript types instantly. This helps reduce runtime bugs, improves IntelliSense, and makes API integrations faster and more reliable. Everything runs locally in your browser.

Typed models are essential when working with APIs. They act as a contract between your data and your code, ensuring that missing keys, unexpected nulls, or type mismatches are detected early. By generating interfaces directly from real API responses, you get a reliable baseline that mirrors actual data structures.

What this generator produces

• TypeScript interface definitions based on your JSON.
• Nested interfaces for nested objects.
• Array types inferred from sample data.
• Basic scalar types: string, number, boolean.

How to use the tool

1. Paste JSON on the left.
2. Click Generate Models.
3. Copy the TypeScript output on the right.

Example: JSON to TypeScript

Input JSON:

{
  "id": 7,
  "name": "Avi",
  "active": true,
  "roles": ["admin", "editor"],
  "profile": {
    "email": "avi@example.com",
    "score": 9.5
  }
}

Generated TypeScript:

export interface Root {
  id: number;
  name: string;
  active: boolean;
  roles: string[];
  profile: Profile;
}

export interface Profile {
  email: string;
  score: number;
}

Handling arrays and nested objects

Arrays become typed arrays (e.g., string[]), and nested objects become separate interfaces. If an array contains objects, the generator creates a new interface for those objects and references it in the array type.

Common errors and fixes

• Invalid JSON: Fix syntax issues with JSON Validator.
• Mixed array types: Arrays with multiple types may lead to any. Normalize values or use a representative sample.
• Null values: Nulls are treated as any. Provide non-null samples for accurate typing.
• Unexpected interface names: Names are inferred from keys; rename interfaces after generation if needed.
• Optional fields missing: Optionality is inferred from the sample. Include optional fields in the sample or mark them optional manually.

Best practices for TypeScript models

• Use representative API samples that include all fields.
• Mark optional fields with ? after generation when needed.
• Consider using readonly if models should be immutable.
• Keep interfaces in a dedicated types folder for clarity.
• Validate JSON with JSON Schema Validator when strict contracts are required.

Optional fields and unions

TypeScript supports optional fields and union types, but they are hard to infer from a single sample. If a field may be missing, mark it as optional with ?. If a field may contain multiple types, use a union like string | null or number | string after generation. These refinements make your models more accurate for real-world APIs.

For example, if your API sometimes returns null for a value, update the type to include null. This prevents runtime errors and encourages explicit null handling in your code.

Runtime validation pairing

TypeScript types are compile-time only. For runtime safety, pair generated interfaces with validation libraries like Zod or AJV. Use JSON Schema Validator to confirm payload shape, then generate TypeScript types for developer ergonomics. This combination gives you both runtime safety and strong IDE support.

Example: typing API responses

After generating interfaces, you can use them like this:

async function fetchUser(): Promise<Root> {
  const res = await fetch("/api/user");
  const data = await res.json();
  return data as Root;
}

For stricter safety, validate the response before casting.

Use cases

Frontend apps: Type API responses to prevent UI errors.

Node.js services: Enforce consistent data structures across services.

SDKs: Generate types for client libraries.

Testing: Use typed fixtures to catch mismatches early.

Common pitfalls

• Optional fields missing: Add ? to optional fields manually.
• Date strings: Dates are inferred as string. Use a Date wrapper or parser.
• IDs as strings: IDs may be strings even if they look numeric. Confirm with real payloads.
• Deep nesting: Deep structures can be hard to manage; consider flattening or splitting types.

TypeScript integration tips

Generated interfaces work well with fetch wrappers, Axios, and GraphQL clients. Use them to type API responses, request bodies, and state objects. For example, define type UserResponse = Root and use it in your hooks to gain full type safety.

Workflow checklist

1. Validate JSON input.
2. Generate interfaces and review names.
3. Mark optional fields if required.
4. Store types alongside API clients.
5. Update types when the API changes.

Team workflow tips

Keep generated types in version control and review diffs when APIs change. This creates a visible contract between backend and frontend teams. For large projects, centralize types in a shared package so multiple apps can reuse the same models.

If you rely on multiple API versions, store types in separate folders (e.g., v1, v2) so migrations are clear and backward compatibility is easier to manage.

Interoperability with runtime validators

TypeScript types do not validate data at runtime. If you need runtime checks, use a schema or runtime validator and generate types from the same source. This ensures your compile-time and runtime models stay aligned.

FAQs

Does this generate types or interfaces?
It generates interfaces by default, which you can convert to types if preferred.

Can I generate types for arrays at the root?
Yes. Wrap arrays in an object for clearer naming if needed.

Is my JSON uploaded?
No. Everything runs locally in your browser.

Does it infer optional fields?
Optionality is based on the sample. Mark fields optional manually if needed.

Can I use this for API contracts?
Yes, but pair it with schema validation for strict enforcement.

How do I handle unions?
Unions are not automatically inferred; you can edit the output if needed.

Can I generate enums?
Enums require manual definition after generation.

Does it support nested arrays?
Yes. Arrays of objects generate nested interfaces.

Can I use this with React?
Yes. Use generated interfaces to type props, state, and API hooks.

Do I need to regenerate types often?
Regenerate when your API changes, and compare diffs to update models.

Does it generate classes?
This tool generates interfaces. If you need classes, create them manually or use the Java/C# tools.

Can I use these types in Node.js?
Yes. They work with any TypeScript project, including backend services.

How do I handle API versioning?
Create separate type files per version and update clients gradually.