Free Online JSON to TypeScript Converter — No Signup Required
JSON to TypeScript Online — Generate Interfaces from JSON
Paste a JSON sample and get clean TypeScript interfaces — nested objects become their own interfaces, arrays are typed, optional fields and unions are inferred. Fast, secure, and entirely in your browser.
Conversion runs locally. Your JSON never leaves your device.
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Accurate Inference
Optional fields, unions and nested interfaces from your sample.
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Clean Output
Readable interfaces with your root name and export keyword.
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Fast & Free
Handles large payloads with no signup and no limits.
How It Works
Convert JSON to TypeScript in 4 Steps
No installation, no signup. Results in milliseconds.
01
Paste JSON
Paste a representative JSON sample into the input panel.
02
Set Options
Name the root interface and toggle the export keyword.
03
Convert
Click Convert and the interfaces appear instantly.
04
Copy or Download
Copy the interfaces or download them as a .ts file.
The Basics
What Is a JSON to TypeScript Converter?
A JSON to TypeScript converter reads a sample of JSON and writes the TypeScript interfaces that describe its shape. Instead of typing out every field by hand from an API response, you paste the response and get a typed contract you can drop straight into your code.
Why generate types from JSON
Most JSON you work with comes from an API you do not control. Hand-writing interfaces for a large response is slow and error-prone. Generating them from a real sample means the types match the data exactly, and TypeScript then catches mismatches at compile time.
What the converter infers
Nested objects, each as its own named interface.
Arrays, typed by their element (string[], User[]).
Optional fields, when a key is missing from some array items.
Union types, when a field or array holds more than one type.
These are the inference rules the converter applies so the output is predictable.
JSON
Becomes in TypeScript
Object { }
An interface with one field per key.
Nested object
Its own named interface, referenced from the parent field.
Array [ ]
A typed array such as string[] or User[].
Array of objects
One merged interface; keys missing from some items become optional (?).
string / number / boolean
string / number / boolean.
null
null, or a union like string | null when mixed.
Mixed-type array
A union element type, for example (number | string)[].
Optional fields and unions
When you paste an array of objects, the converter merges them into one interface. A key that appears in every item is required; a key missing from any item is marked optional with a ?. When a single field holds different types across the sample, it becomes a union, so the interface stays accurate for every record. Validate the JSON first with the JSON parser if it will not convert, or tidy it in the JSON formatter.
When you see any
An empty array or object gives the converter nothing to infer from, so it falls back to any[] or any. Paste a representative sample with those fields populated to get precise types. For a deeply nested payload, expanding it in the JSON viewer first helps you confirm the shape before you convert.
Walkthrough
A Worked Example: Order Payload to Interfaces
See how a nested object with an array of items becomes clean, typed interfaces.
Notice three things: items became its own Item interface and a typed array, qty is optional because the second item omits it, and coupon is typed null from the sample. For the step-by-step reasoning, see our guide on generating TypeScript interfaces from JSON.
Use Cases
When to Convert JSON to TypeScript
Typed contracts from real data, in seconds.
Type API Responses
Turn a real response into interfaces your code can rely on.
Generate DTOs
Create data-transfer types for a service from sample payloads.
Migrate JS to TS
Add types to an existing codebase from the data it already handles.
Type Mock Data
Give fixtures and mock responses matching interfaces.
Config Typing
Type a JSON config file so edits are checked at compile time.
Learning
See how JSON shapes map onto TypeScript's type system.
FAQ
Frequently Asked Questions
Everything developers ask about generating TypeScript from JSON.
It reads a JSON sample and generates TypeScript interfaces that describe its shape, inferring the type of every field. Nested objects become their own interfaces and arrays become typed arrays. Everything runs in your browser.
Yes. Each nested object becomes its own named interface referenced from the parent, and arrays become a typed array such as string[] or User[], with the element type inferred from the items.
When an array contains several objects, a key that is present in some items but missing from others is marked optional with a question mark, so the interface matches every record in the sample.
A null is typed as null, and when a field holds both a value and null across the sample it becomes a union such as string | null, so the interface stays accurate.
Objects become interfaces. A top-level array or a primitive root becomes a type alias, for example type Root = User[], since those cannot be expressed as a single interface.
No. Conversion runs entirely in your browser using JavaScript. Your JSON is never uploaded, never stored, and never logged, so it is safe for sensitive payloads.
An empty array or object has no sample data to infer from, so it becomes any[] or any. Paste a representative sample with those fields populated to get precise types.
The types are inferred from the exact sample you paste, so a representative example with every field populated gives the best result. Validate the JSON first with the JSON parser if it will not convert.