DEV-TRAFFIC-169 · Generator

JSON to TypeScript Generator

Infer TypeScript interfaces or type aliases from a concrete JSON value without uploading the data.

Embed Report issue

Root type Declaration Make properties optional

JSON input116 characters

TypeScript outputWaiting for input

ProcessingBrowser-firstStorageNone by defaultAccessNo account required

WORKED EXAMPLE

JSON to TypeScript Generator example

Generated with ToolRecord as the root name and Interface selected.

Example input

{
  "id": 42,
  "owner": { "name": "Ada", "active": true },
  "tags": ["tools", "typescript"]
}

Expected output

export interface ToolRecord {
  id: number;
  owner: Owner;
  tags: string[];
}

export interface Owner {
  name: string;
  active: boolean;
}

INSTRUCTIONS

How to use JSON to TypeScript Generator

1
Paste valid JSON or load the sample.
2
Choose a root type name and interface or type-alias output.
3
Optionally mark every generated property as optional.
4
Choose Generate TypeScript, then copy or download the .ts output.

PURPOSE

What this tool does

The generator parses JSON and maps strings, numbers, booleans, nulls, arrays, and nested objects to TypeScript types.

Nested objects become named declarations. Arrays combine observed item types, and object arrays mark a property optional when it is absent from one or more sampled objects.

SUPPORTED BEHAVIOR

Features and options

Interface or type-alias output
Custom root name
Nested declaration generation
Primitive and array inference
Observed union types
Optional properties for missing fields in object arrays
Quoted property names when required

IMPLEMENTATION NOTES

Technical information

The engine uses JSON.parse, so the input must follow JSON syntax rather than JavaScript object-literal syntax. It infers only from supplied values; it does not execute code or fetch a schema.

Empty arrays become unknown[]. A null sample becomes null rather than guessing a wider domain type. Numbers map to number because JSON does not distinguish integers from floating-point values.

WHEN IT HELPS

Common use cases

Bootstrapping API response types
Documenting fixture shapes
Creating a first draft for typed data imports
Comparing the observed shape of sample payloads

REVIEW BEFORE USING

Limitations

Generated types describe the sample, not every payload the API may return.
Dates, UUIDs, enums, branded types, integer ranges, and semantic formats are not inferred.
This tool accepts JSON values, not JSON Schema.
Review nullability and optionality against the real API contract before production use.

NEXT LOGICAL TASKS

AUTHORITATIVE MATERIAL

References & Sources

rfc-editor.org · Standards BodyRFC 8259 — The JSON Data Interchange Format

Defines the JSON values and syntax accepted by the parser.

Verified 2026-08-13 ↗typescriptlang.org · Official DocumentationTypeScript Handbook — Object Types

Documents interfaces, object types, optional properties, arrays, and type aliases used in generated output.

Verified 2026-08-13 ↗

QUICK ANSWERS

JSON to TypeScript Generator FAQ

Does this generate runtime validation?

No. It emits compile-time TypeScript declarations only.

Why does an empty array become unknown[]?

An empty sample contains no evidence about its element type, so unknown is safer than inventing one.

Can I provide JSON Schema?

Not in this tool. The registry contains a separate JSON Schema to TypeScript Generator for that workflow.

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