Skip to content
CrateX.app logo

CrateX.app

JSON to TypeScript

JSON to TypeScript converts JSON samples into TypeScript interfaces and type aliases locally, with optional fields, union/null/Date inference, root naming, and .ts copy/download.

JSON

Characters

0 / 50,000

TypeScript
JSON to TypeScript

Quick Start

1
Paste a valid JSON sample into the left editor.
2
Optionally set the root type name, such as ApiResponse.
3
Review TypeScript on the right: objects become interface; arrays or primitives become type alias.
4
Copy or download the generated .ts; input actions handle the JSON sample.

Common Scenarios

Turn real API responses into TypeScript types you can use immediately in frontend pages, SDK clients, or integration tests.

Before formalizing an API contract, inspect how optional fields, null values, and union types are inferred from real JSON samples.

Convert mock JSON data into quick type definitions for fixtures, Storybook stories, or prototypes.

When backend payloads change, use the latest JSON sample to review whether nested declarations like User or Meta also need updates.

Usage Advice

Use a representative JSON sample. This is sample-based inference, so missing fields or values cannot appear in the output.
Empty arrays become unknown[], and empty objects become interfaces extending Record<string, unknown> until you provide richer sample data.
Nested declarations are normalized from property names, so newer output prefers names like User or Meta instead of older root-prefixed forms.
Generation only runs on valid JSON. Fix syntax errors first; the editor shows line and column details when parsing fails.
Valid custom root names are preserved as-is, while invalid names are normalized to a legal PascalCase TypeScript identifier.

Type Inference Boundaries

The generator infers from the current sample, not from JSON Schema, OpenAPI, GraphQL, files, URLs, JSON Lines, or batch samples.
Arrays merge observed item shapes: fields missing from some items become optional, and null or mixed values become unions.
Date-like strings may be inferred as Date, but the runtime JSON value is still a string unless your code parses it.
Object roots generate interface; arrays and primitive roots generate type aliases; empty arrays use unknown[] and empty objects extend Record<string, unknown>.
The root name defaults to Root. Legal custom names are preserved, while invalid names and reserved words are normalized to PascalCase.
The output is static TypeScript declarations only: no runtime validator, parser, serializer, Zod/Yup/io-ts schema, or API client.

Limitations & Compatibility

This tool infers types from sample data, not from a formal schema or contract source of truth. Fields missing from your sample cannot be guessed.
Input must be strict JSON. Comments, trailing commas, and other JavaScript-only syntax are rejected.
Generated TypeScript code does not include export statements. Downloading a .ts file is separate from adding the export keyword your project may require.
The result is static TypeScript code only. It does not create runtime validators, parsers, serializers, Zod schemas, or API clients.

Privacy & Security

JSON to TypeScript runs locally in your browser. JSON input may stay as a browser draft. If a saved workspace or WebDAV sync is enabled, the JSON input, root type name, input/output line-number preferences, and wrapping preferences may be saved through that sync. Generated TypeScript, validation errors, line/column highlights, copy state, and undo history are derived from the current input and are not saved as separate result data. Input JSON downloads and .ts output downloads are created only when you click Download. This tool does not upload files or create attachments.

FAQ

6

Continue with these related tools for the next step.

About

About Us
Pricing

Legal

Terms
Privacy Policy
Cookie Policy

Preferences

Manage Cookies

All tool processing happens locally in your browser.