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JSON to TypeScript

Converters

Paste a JSON response and get TypeScript interfaces, type aliases or a Zod schema — nested types named, optional fields worked out from your samples.

  • Converter
  • JSON
  • Runs offline
  • TypeScript
Output
An array of objects is merged
TypeScript
export interface Order {
  orderId: string;
  placedAt: string;  // ISO 8601 date-time
  customer: Customer;
  items: Item[];
  total: number;
  notes: unknown;
  coupons: unknown[];
}

export interface Item {
  sku: string;
  quantity: number;
  unitPrice: number;
  discountRate?: number;
}

export interface Customer {
  id: number;
  email: string;
}

TypeScript types from a JSON sample

Paste a response from an API and get the types that describe it: one interface per object, nested ones named after their keys, optional fields where a key is missing from some samples, and unions where values differ. Paste an array of objects and they are merged, so one sample fills the gaps of another.

A sample shows what was sent, not everything that can be sent. Treat the result as a first draft and check optional fields, unions and anything typed unknown against the API's documentation.

  • InterfaceThe usual choice for object shapes; can be extended and merged.
  • Type aliasThe same shape as a type; needed for unions and mapped types.
  • Zod schemaValidates data at runtime and infers the type from the schema.
  • unknown, not anyEmpty arrays and always-null fields stay unknown until you know better.

How to use the converter

  1. Paste a JSON sample — or an array of several, to merge them.
  2. Pick the output: Interface, Type or Zod Schema.
  3. Set the Root Name; nested types are named after their keys, in singular for array items.
  4. Read the notes: optional fields, empty arrays and integers too large for JavaScript are called out.
  5. Copy the code or download it as a .ts file.

Examples

Type an API response

A user object with a nested plan, a nullable email and a date.

Merge array items

Two order lines; the discount only one has becomes optional.

Validate it at runtime

The same order as a Zod schema, with dates checked as ISO strings.

Handle awkward keys

Keys with dashes or digits are quoted; a 64-bit ID gets a warning.

Frequently asked questions

Interface or type?

For object shapes either works. Interfaces can be extended and merged, and their errors read a little better; type aliases are needed for unions and mapped types. Pick one and stay consistent.

What is the difference between "?" and "| null"?

email?: string means the key may be missing. email: string | null means the key is always there but may be null. The converter uses ? when a key is missing from some merged samples and | null when a sample had null.

Why does a number have a warning?

JavaScript numbers are exact only up to 2^53. A larger integer — a 64-bit ID, for example — is rounded by JSON.parse. Have the API send it as a string, or parse it as a bigint.

Do these types check data at runtime?

No. TypeScript types disappear when the code is compiled, so a response that does not match them goes unnoticed. Choose Zod Schema to validate data when it arrives.

Is my JSON sent anywhere?

No. The types are generated in your browser; check the Network tab in your developer tools.

Related tools

JSON to PydanticThe same sample as Python models.JSON Formatter & ValidatorFix or unescape the JSON first.Diff CheckerCompare two responses to see which fields change.

Learn more

Python in PracticeWorking with JSON and External DataValidating the shape of data you did not create before trusting it.Building Reliable AI SystemsStructured Output You Can TrustSchemas, validating at the boundary, and repair loops that converge.