Is the JSON data I enter sent to a server?

No. All parsing and type generation processes are executed locally within your browser. Since no data is ever sent to or stored on external servers, it is completely safe to use with real or sensitive data.

Can it correctly convert JSON containing Japanese keys (property names)?

Yes, it can. In accordance with TypeScript syntax rules, keys containing special characters or non-English characters like Japanese are safely output as properties enclosed in quotes ("").

Should I output as interface or type?

It depends on your project's coding standards. Generally, 'interface' is recommended for defining object structures or when you plan to extend them via declaration merging. On the other hand, 'type' tends to be preferred in environments that require complex type manipulations like Union types.

What happens if an array contains objects with different structures?

The tool's optional inference feature will compare and scan all objects within the array. Keys common to all objects will be output as 'required properties', while keys present in only some objects will be smartly merged and output as 'optional properties (?)'.

Can it convert deeply nested JSON data?

Yes. Because the parsing is recursive, there is theoretically no limit to the depth of nesting. Inner objects are automatically extracted as individual interfaces and organized so they connect to the top-level root type.

🧩

json to ts,

JSON to TypeScript Interface Generator

Instantly generate TypeScript type definitions (Interface/Type) by simply pasting JSON data.
Supports nested structures and smart optional property inference.

⚡

Instant Conversion

Real-time

🔒

Browser Processing

Safe & Fast

🧠

Smart Inference

Advanced Parsing

🔒

100% In-Browser Processing: The JSON data you enter is never sent to a server. You can safely convert sensitive information like API keys.

Root Name:

Output Mode:

Infer Optional(?) Add readonly

{} JSON Input

TS TypeScript Output

about,

What is JSON to TypeScript Interface Generator?

A free tool for developers that instantly generates TypeScript type definitions (Interface or Type Alias) just by pasting JSON data. It automates tasks prone to manual errors, such as creating type definitions for API integration or typing mock data.

Not only does it automatically expand nested and complex JSON structures, but it also features advanced logic that analyzes objects in arrays to infer optional properties (?).

All conversion processing is completed within your browser. The entered JSON data is never sent to or saved on external servers, allowing you to safely convert sensitive business data or production API response data.

how to,

How to Use This Tool

STEP 1

Paste JSON

Paste the target JSON data into the input area on the left panel. You can directly paste API responses or database query results. The parsing process will execute in real-time.

STEP 2

Adjust Settings

From the top menu, adjust settings like the Root Name, output mode (interface or type), optional inference toggle, and readonly modifiers to fit your project's coding standards.

STEP 3

Copy & Use

Check the instantly generated TypeScript code in the right panel and click the "Copy" button. Simply paste it into your project editor to start type-safe development.

glossary,

TypeScript Type Definition Glossary

Interface: A syntax in TypeScript for defining object structures and class implementations. Written like interface User { name: string; }, it has the characteristic of allowing declaration merging when multiple interfaces with the same name are defined.
Type Alias: A feature that gives a name to a type using the type keyword. It is similar to Interface but more flexible, as it can define not only objects but also primitive types, Union types, and Mapped Types.
Union Type: A typing that allows a variable to hold one of several types. Represented by joining types with a pipe symbol (|) like string | number, often used when API responses can vary.
Optional Property: A setting that allows a property to be absent (undefined) by appending ? to the end of the property name. It is an essential concept when data in arrays lacks uniformity.
Readonly Modifier: By adding readonly before a property, it prevents the reassignment (modification) of the property's value after the object is created at the compiler level. It is useful for guaranteeing immutable data structures.

faq,

Frequently Asked Questions

Q.Is the JSON data I enter sent to a server?: No. All parsing and type generation processes are executed locally within your browser. Since no data is ever sent to or stored on external servers, it is completely safe to use with real or sensitive data.
Q.Can it correctly convert JSON containing Japanese keys (property names)?: Yes, it can. In accordance with TypeScript syntax rules, keys containing special characters or non-English characters like Japanese are safely output as properties enclosed in quotes ("").
Q.Should I output as interface or type?: It depends on your project's coding standards. Generally, 'interface' is recommended for defining object structures or when you plan to extend them via declaration merging. On the other hand, 'type' tends to be preferred in environments that require complex type manipulations like Union types.
Q.What happens if an array contains objects with different structures?: The tool's optional inference feature will compare and scan all objects within the array. Keys common to all objects will be output as 'required properties', while keys present in only some objects will be smartly merged and output as 'optional properties (?)'.
Q.Can it convert deeply nested JSON data?: Yes. Because the parsing is recursive, there is theoretically no limit to the depth of nesting. Inner objects are automatically extracted as individual interfaces and organized so they connect to the top-level root type.

use cases,

Use Cases

🔌

API Integration

Paste response JSON retrieved from external REST APIs during frontend development to instantly create type definitions, allowing for rapid implementation of type-safe fetching.

📦

NoSQL Type Definitions

Automatically generate TypeScript models from the document structure (JSON) of schemaless databases like MongoDB or Firestore to ensure type consistency.

📋

Code Review Support

Quickly generate type definitions from sample JSON data shared on Pull Requests, serving as an auxiliary tool for reviewers to verify type safety.

🎓

Learning TypeScript

It helps as a learning tool for Interface design by visually and immediately showing how JSON data is mapped into type structures in the TypeScript world.

tech,

Technical Details

This tool relies on no external parsing libraries and is implemented using a custom recursive type inference algorithm written in Vanilla JavaScript.

It traverses an AST-like object tree safely evaluated with JSON.parse() to classify primitive types (based on typeof) and object types. Especially in parsing arrays, it collects types of internal elements and computes unions and optional properties rapidly through comparative set operations.

The syntax highlighting of the generated code is also handled by lightweight regex replacements instead of AST parsing, ensuring a snappy performance without blocking the browser's main thread.