JSON to TypeScript Converter

Already have a JSON Schema contract? Use JSON Schema to TypeScript to generate declarations from required fields, enums and references instead of inferring them from sample values.

Why generate TypeScript types from JSON?

Writing interfaces for a large API response by hand is slow and error-prone. It's easy to miss a nested field or a property that is sometimes absent. Generating them from a real response gives you an accurate starting point in seconds. Then you can rename types, tighten string to literal unions, or add comments.

Example

{
  "id": 7,
  "title": "Ship v2",
  "assignee": {
    "id": 3,
    "name": "Grace"
  },
  "labels": [
    "backend",
    "urgent"
  ],
  "comments": [
    {
      "author": "Grace",
      "body": "On it",
      "editedAt": null
    },
    {
      "author": "Linus",
      "body": "LGTM"
    }
  ]
}

export interface Issue {
  id: number;
  title: string;
  assignee: Assignee;
  labels: string[];
  comments: Comment[];
}

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

export interface Comment {
  author: string;
  body: string;
  editedAt?: null;
}

Notice how the generator:

• created a separate Assignee interface for the nested object;
• named the array item type Comment by singularizing comments;
• marked editedAt as optional because only one of the two comments had it;
• typed labels as string[].

How type inference works

Keys that aren't valid identifiers, like first-name, are quoted automatically. Objects with an identical structure share one interface instead of being duplicated.

Tips for better results

• Use real data with variety. Include array items that show optional fields and nulls, so the generator can see them.
• Review string fields. A status: "open" field is inferred as string. Narrow it to "open" | "closed" if you know the possible values.
• Dates are strings in JSON. Keep them as string in the type, and convert them to Date at the edges of your app.
• Validate at runtime. Types don't check data coming from the network. Pair them with a Zod schema.

Need a repeatable test payload? Build one with Mock Data Generator. For a backend model, choose JSON to Rust or JSON to PHP and review each target language’s number and optional-field rules.

Frequently asked questions