JSON to TypeScript Interface

About this tool

Typing API responses by hand is slow and error-prone. This converter reads a JSON sample and generates TypeScript interfaces for the whole structure — nested objects become named interfaces, arrays of objects are merged into a single shape, and keys that are missing from some items can be marked optional.

The result is ready to paste into your codebase, with or without export keywords.

How to use it

1. Paste a representative JSON response.
2. Set the root interface name (default Root).
3. Toggle optional detection, export and semicolons to match your style.
4. Copy or download the generated .ts file.

Useful ways to apply it

• Typing REST API responses without writing interfaces by hand.
• Generating types from fixture files in tests.
• Onboarding a legacy untyped payload into a TypeScript project.
• Quickly checking what shape a third-party webhook actually has.

Worked example

{"id":7,"name":"Ada","nickname":null,"tags":["api","json"]}

interface Root { id: number; name: string; nickname: null; tags: string[]; }

Edge cases to check

• One sample cannot prove whether a property is optional in every real payload.
• Empty arrays provide no element-type evidence.
• Mixed-type arrays and null values need manual review against the real API contract.

Known limitations

Generated interfaces are an inference from sample data, not runtime validation and not a replacement for an API schema.