JSON to TypeScript: Generate Interfaces Without Uploading Your Data (2026)

To convert JSON to TypeScript interfaces without uploading your data, open DevTools → Network tab before pasting — a browser-based converter makes zero outbound requests. Most online "JSON to TypeScript" tools send your payload to a server for processing; a client-side implementation runs the same type-inference logic locally in JavaScript.

Step-by-step: convert JSON to TypeScript

1. Open brevio JSON to TypeScript and set a root interface name (e.g. User, Order, or ApiResponse).
2. Paste your JSON object into the input area.
3. Click Generate TypeScript — interfaces appear for the root object and all nested objects.
4. Click Copy and paste the interfaces directly into your TypeScript project or type declaration file.

Example: before and after

Input JSON

{
  "id": 1,
  "name": "Alice",
  "email": "alice@example.com",
  "active": true,
  "score": 98.5,
  "tags": ["admin", "user"],
  "address": {
    "street": "123 Main St",
    "city": "Berlin",
    "zip": "10115"
  }
}

Generated TypeScript

export interface Address {
  street: string;
  city: string;
  zip: string;
}

export interface User {
  id: number;
  name: string;
  email: string;
  active: boolean;
  score: number;
  tags: string[];
  address: Address;
}

How the type inference works

The converter walks the JSON tree recursively and maps each value to the narrowest TypeScript type that accurately represents it:

Nested objects are extracted into separate named interfaces. The interface name is derived from the JSON key using PascalCase conversion — user_profile becomesUserProfile, billing-address becomes BillingAddress.

JSON to TypeScript tool comparison

When JSON privacy matters

Developers often paste JSON samples from real API responses to generate types quickly. These responses may contain:

• Access tokens or API keys in response headers copied alongside the body
• Customer PII (email addresses, user IDs, names) in real data samples
• Internal service response shapes that reveal backend architecture
• Health or financial records from staging or production environments

A client-side converter removes the upload risk entirely. The same type-inference logic runs in your browser — no data touches a server.

Post-processing tips

• Optional fields: The generator produces key: type for every key present in your sample. If a field can be absent, change it to key?: type.
• null vs undefined: null values generate nulltypes. If a field can also be absent, use key: string | null or key?: string | null.
• Large arrays: Type inference uses the first element. If array elements have varying shapes, inspect the output and add a union type manually.
• Zod schemas: Once you have the TypeScript interface, you can hand-write a corresponding Zod schema for runtime validation using the same field names and types.

Generate types from JSON in the terminal

For CI workflows or bulk conversion, quicktype is the standard open-source CLI tool:

npx quicktype -s json -o User.ts --lang typescript input.json

quicktype supports JSON, JSON Schema, GraphQL, and TypeScript sources, and generates types for 20+ target languages. It runs locally when invoked via npx.

Related tools and guides

• JSON Formatter — validate and pretty-print JSON before converting
• SQL Formatter — format SQL queries with zero upload
• How to format SQL without uploading