Free tools

Free JSON to TypeScript Interface Generator

Paste JSON data and generate TypeScript interfaces with optional root naming for API client and schema workflows.

Copy-paste outputs

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Tool 01

JSON to TypeScript Interface Generator

Generate TypeScript interfaces from nested JSON payloads for safer client/server code.

JSON to TypeScript Interface Generator

Generate TypeScript interfaces from API payloads and nested JSON objects.

Root interface name

JSON input

Generated TypeScript

export interface Apiresponsecompany {
  name: string;
  active: boolean;
  plans: string[];
}

export interface Apiresponsemetrics {
  mrr: number;
  arr: number;
}

export interface Apiresponse {
  company: Apiresponsecompany;
  metrics: Apiresponsemetrics;
}

How it works

JSON to TypeScript Interface Generator: methodology and worked example

How this tool computes its result

Recursively infers TypeScript types from JSON structure using a GeneratorContext to track named interfaces and prevent duplicate interface names. For objects, it generates an interface with typed fields; for arrays, it infers element type and returns T[]; for primitives, it returns string/number/boolean/null/unknown. Null values are marked optional (?). Generated interfaces are exported and referenced by name. If the root is a primitive or simple array, the output is a type alias instead of interfaces.

Worked example

JSON {"company":{"name":"Brand Armor AI","active":true},"metrics":{"mrr":12500}} generates: interface Company with name: string, active: boolean; interface Metrics with mrr: number; type ApiResponse = {company: Company, metrics: Metrics}. Each nested object becomes its own interface.

When not to use this tool

This infers types from data alone - it does not add custom types (like Date for date strings), does not enforce constraints (min/max length, regex patterns), and does not handle union types beyond null-ness; for API contracts, write TypeScript manually or use tools that parse OpenAPI/GraphQL specs.

Common mistakes

- Pasting JSON with inconsistent types for the same field across multiple objects (e.g., sometimes "id" is a string, sometimes a number) - the tool infers the union of all types found (string | number), which may not be your intention; validate your JSON data first.
- Expecting generated types to be immediately production-ready - the output is a starting point; you should review, add JSDoc comments, tighten optional fields, and adjust constraints based on your API contract.
- Naming the root interface something too generic (e.g., "Data") - the tool defaults to "ApiResponse" if no root name is provided; use a meaningful name like "UserProfile" or "ProductResponse" for clarity.

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