TypeScript to JSON Converter – Complete Guide

What Is a TypeScript to JSON Converter?

A TypeScript to JSON Converter takes TypeScript interface or type definitions and generates corresponding JSON objects with sensible default values for each field type. This is the reverse operation of JSON-to-TypeScript generation — instead of inferring types from data, you create data from types. The tool is invaluable for developers who need mock data, API fixtures, test payloads, or seed scripts based on their existing TypeScript type definitions.

Our converter parses TypeScript interface syntax client-side and maps each property type to an appropriate default value. No code is uploaded to any server.

How the Conversion Works

The converter uses pattern matching to extract property names and types from your TypeScript interface definition. For each property, it generates a sensible default value:

• string → "example_string"
• number → 0
• boolean → false
• Date → "2026-01-01T00:00:00.000Z"
• string[] or Array<string> → ["example_string"]
• Record<string, any> → {}
• Union types → Uses the first variant
• Optional properties (marked with ?) → Still included with default values

Step-by-Step Usage

1. Paste your TypeScript interface into the left input panel.
2. The converter automatically generates a matching JSON object.
3. Use 📄 Sample to load an example interface.
4. Click 📋 Copy to copy the JSON output.
5. Modify the generated defaults to match your test scenario.

Common Use Cases

API Mock Data

When building frontend components before the backend is ready, you need realistic mock data that matches your TypeScript types. This converter generates correctly structured JSON that satisfies your interfaces.

Test Fixtures

Unit tests and integration tests often require sample data. Instead of manually creating JSON that matches your types, generate it automatically and adjust specific values for each test case.

Database Seed Scripts

For MongoDB, PostgreSQL, or any database, you can generate seed data that matches your data models by converting your TypeScript entity interfaces to JSON documents.

API Documentation

When documenting REST endpoints, you need example request and response bodies. Converting your TypeScript DTOs to JSON gives you accurate examples that stay synchronized with your codebase.

Postman/Insomnia Collections

Generate request body templates for API testing tools by converting your TypeScript request types to JSON.

Supported TypeScript Syntax

The converter handles the most common TypeScript type patterns:

• Interface declarations: interface User { ... }
• Type aliases: type Config = { ... }
• Optional properties: name?: string
• Primitive types: string, number, boolean, null, any, unknown
• Array types: string[], Array<number>
• Record types: Record<string, any>
• Union types: "admin" | "user" | "guest"
• Date type: Maps to ISO 8601 string format

Limitations

The converter performs static text analysis rather than full TypeScript AST parsing. Complex features like generics, conditional types, mapped types, and cross-file type references are not supported. For these advanced cases, consider using TypeScript compiler APIs or tools like ts-morph.

Related Tools

• JSON to TypeScript — Generate TypeScript interfaces from JSON
• TypeScript to JavaScript — Strip types from TypeScript
• JavaScript to TypeScript — Add types to JavaScript
• JSON Viewer — Explore generated JSON data
• JSON Validator — Validate JSON correctness