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JSON to TypeScript

Generate a TypeScript interface from representative JSON objects, arrays and primitive values, with a configurable root interface name.

Generate a TypeScript interface Infer nested object shapes Infer arrays from the first item Map strings, numbers, booleans and null
INPUT Sample JSON *
0 chars0 words0 lines

Tool settings

Ctrl / ⌘ + Enter
TypeScript
About the tool

What JSON to TypeScript does

JSON to TypeScript converts one representative JSON value into a TypeScript interface. Object properties become typed fields, nested objects become inline object types and arrays receive an item type inferred from the first element.

This is useful for quickly describing API response samples, fixtures and configuration objects. The generator is deterministic and does not call an external AI service, but it can only infer what appears in the sample. It cannot know whether a field is optional, whether several numeric values form a literal union, or whether a null example should also allow another type.

JSON to TypeScript input and generated interface
Generate a starting interface, then review it against the complete data contract.

How to use

  1. Choose representative JSON. Include the fields and value types that the real payload can contain.
  2. Name the interface. Enter a TypeScript-safe root name such as ApiUser.
  3. Generate. The tool parses JSON and maps its visible values to TypeScript types.
  4. Review inference. Check empty arrays, mixed arrays, null values, optional fields and unusual property names.
  5. Compile and test. Paste the result into the target project and run its TypeScript checks before relying on it.
Built for the task

Why use JSON to TypeScript?

Focused controls, predictable output, and a workflow designed around this exact transformation.

01

Fast interface draft

Turn a realistic JSON sample into copy-ready TypeScript without writing every field manually.

02

Nested object support

Preserve the visible hierarchy as inline object and array types.

03

Configurable root name

Set a meaningful exported interface name for the generated source.

04

Visible inference limits

Review the exact cases where one sample cannot describe a complete contract.

Useful answers

Questions about JSON to TypeScript

Practical details about input, output, privacy, limits, and the best way to use this tool.

01 Does the generator create optional properties?

No. Every property visible in the sample is generated as required. Add optional markers manually when the API can omit a field.

02 How are arrays inferred?

A non-empty array uses the first item as its item-type example. An empty array becomes unknown[]. Review heterogeneous arrays manually.

03 What happens to null?

A null sample becomes the null type. If the field may also hold another value, change it to a union such as string | null.

04 Does it create multiple named nested interfaces?

No. Nested objects are represented as inline object types inside the root interface.

05 Can it infer dates or URLs?

No. JSON represents those values as strings, so the generator returns string.

06 Does it call an AI API?

No. Core generation is performed with deterministic local rules.

07 Why must I compile the result?

Property names and project conventions vary. Your TypeScript compiler and actual API contract are the final checks.

08 What JSON roots are supported?

Objects generate their fields directly. A root array or primitive is wrapped in an interface with a value property.

Learn JSON

Read the complete JSON Guide

Learn JSON objects, arrays, value types, validation, formatting, parsing, API workflows, and common syntax errors.

  • Objects, arrays, and values
  • Validation and formatting
  • API and parsing workflows
Read guide Practical explanations and examples

How JSON values map to TypeScript

JSON strings map to string; integers and decimals map to number; booleans map to boolean; and null maps to null. Objects become nested property blocks. Arrays use the inferred type of the first item, while empty arrays use unknown[].

Why representative input matters

A single payload is an observation, not a complete schema. If one response contains a value and another omits it, the generator cannot infer the optional property from the first response. The same limitation applies to nullable fields, mixed arrays and string values that follow a specific format.

Review property names

The generator normalizes characters that cannot appear in a simple TypeScript identifier. Review keys containing spaces, punctuation, hyphens or leading digits. In some contracts it is better to preserve an unusual JSON key as a quoted property name rather than accept a normalized name.

Validate before generating

The input must be valid JSON, including double-quoted property names and strings. Use JSON Validator to diagnose syntax problems and JSON Schema Validator to check an explicit data contract.

Choose the next type layer

A TypeScript interface describes compile-time structure and does not validate untrusted values at runtime. Continue with JSON to Zod Schema for TypeScript runtime validation or JSON to Pydantic Model for Python validation models.

Primary references

See the TypeScript handbook on object types and RFC 8259 for JSON syntax.