Why does the tool generate multiple interfaces?

Each nested object in your JSON becomes its own named TypeScript interface. This matches standard TypeScript conventions where complex shapes are defined as separate named types rather than anonymous inline objects. The interfaces are linked by name — the parent interface references the child interface name as its field type. The root interface always appears first, with dependencies listed below.

How are array element types detected?

When a field is an array of objects, the tool merges all element objects to build a combined field list. Fields that appear in every element are required; fields that appear in only some elements are marked optional with ?. This gives you a union of all possible shapes in a single interface. The interface name is derived by singularizing the array key name — for example, items becomes Item, users becomes User, and categories becomes Category.

What does the null comment mean?

When a JSON value is null, the inferred TypeScript type is also null. This is structurally correct but usually not the final type you want — null is a placeholder because the sample JSON does not show the real value. The comment // replace null with actual type is a reminder to update the field to its true type, such as string | null or Date | null, once you know what the API actually returns for that field.

Can I use this with JSON arrays at the root?

No. The tool requires the root input to be a JSON object that starts with { and ends with }. A JSON array at the root cannot be mapped to a single named interface without a wrapper. To convert a JSON array, wrap it in an object first, for example { "items": [...] }, then generate the interface and extract the element interface from the output.

Does this handle keys that are not valid JavaScript identifiers?

Yes. Keys that contain hyphens, spaces, or other special characters are quoted in the interface output. For example, a key named content-type becomes 'content-type': string and a key named my field becomes 'my field': string. These fields must be accessed with bracket notation in TypeScript: obj['content-type'].

Is this the same as quicktype or json-schema-to-typescript?

The tool performs the same core task — inferring TypeScript interfaces from a JSON sample — but runs entirely in your browser without any server calls or dependencies. Dedicated tools like quicktype offer more advanced features such as discriminated unions, date detection, and multi-language output. This tool focuses on fast, clean interface generation for everyday API responses and configuration objects, with zero setup required.

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JSON to TypeScript — Interface Generator

Generate TypeScript interfaces from JSON objects instantly. Infers types for strings, numbers, booleans, arrays, and nested objects. Detects optional fields from array element merging, handles null values, and outputs clean, ready-to-use interface definitions.

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How to Use JSON to TypeScript — Interface Generator

How to Use the JSON to TypeScript Interface Generator

Step 1: Paste Your JSON

Paste any valid JSON object into the input panel. The tool immediately analyzes the structure and generates TypeScript interface definitions in the output panel.

Example input:

{
  "id": 1,
  "name": "Alice",
  "active": true,
  "role": "admin"
}

Generated output:

export interface Root {
  id: number;
  name: string;
  active: boolean;
  role: string;
}

Step 2: Set the Root Interface Name

Use the Root name field to set the name of the top-level interface. The default is Root. For example, enter User, ApiResponse, or OrderPayload to generate interface User { ... }.

Step 3: Configure Options

Add export keyword — prepends export to every interface, making them ready for module import/export
Mark null fields as optional — when a field value is null, adds ? to the field and a comment reminding you to replace null with the actual type

Step 4: Nested Objects

Nested objects generate separate named interfaces. The parent field references the child interface name:

export interface Root {
  user: User;
}

export interface User {
  id: number;
  name: string;
}

The root interface always appears first, with nested interfaces below it.

Step 5: Arrays of Objects

Arrays of objects generate a separate interface for the element type. The interface name is derived by singularizing the field key — items[] becomes Item, products[] becomes Product, users[] becomes User. All element objects are merged, so fields that appear in only some elements are automatically marked as optional.

Step 6: Copy and Use

Click Copy TypeScript to copy the full output to your clipboard. Paste it directly into your .ts or .tsx files. You may need to rename interfaces or add more specific types for null fields, but the structure is complete.

Supported Type Mappings

JSON value	TypeScript type
`"string"`	`string`
`42`, `3.14`	`number`
`true`, `false`	`boolean`
`null`	`null`
`[...]` (objects)	`InterfaceName[]`
`[...]` (mixed)	`(string \| number)[]`
`[]` (empty)	`unknown[]`
`{...}` (nested)	`InterfaceName`

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JSON to TypeScript — Interface Generator

How to Use JSON to TypeScript — Interface Generator

How to Use the JSON to TypeScript Interface Generator

Step 1: Paste Your JSON

Step 2: Set the Root Interface Name

Step 3: Configure Options

Step 4: Nested Objects

Step 5: Arrays of Objects

Step 6: Copy and Use

Supported Type Mappings

Frequently Asked Questions

Why does the tool generate multiple interfaces?

How are array element types detected?

What does the null comment mean?

Can I use this with JSON arrays at the root?

Does this handle keys that are not valid JavaScript identifiers?

Is this the same as quicktype or json-schema-to-typescript?

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