JSON to TypeScript — Generate Interfaces Free
Convert JSON to TypeScript interfaces for free. Paste any JSON, get clean type definitions instantly. Browser-based, no signup.
Convert any JSON sample into matching TypeScript interfaces in one click. Paste an API response, a config snippet, or a mock payload — PDFFlare's JSON to TypeScript converter walks the structure, generates a clean interface for every nested object, and infers element types for arrays (with unions for mixed-type arrays).
Everything runs in your browser, so production payloads stay private. Already have JSON that needs cleaning up? Use JSON Formatter to validate and pretty-print first. Need a CSV instead? JSON to CSV has you covered.
Example: an array of objects
For [{"id":1}], the array item and root alias have separate names:
export interface RootItem {
id: number;
}
export type Root = RootItem[];This describes the sample only. If other responses can omit id or return a different value type, adjust the generated definition accordingly.
How to Convert JSON to TypeScript
Paste your JSON
Paste a sample JSON payload — an API response, a config snippet, anything that represents the shape of the data you'll work with.
Convert to TypeScript
Click Convert to TypeScript. Each object becomes its own interface; arrays become T[] (or unions for mixed types). The root type is named Root for ergonomic top-level use.
Copy and paste into your code
Click Copy Output and paste the generated interfaces straight into a .ts file in your project. Rename them to match your domain language as you go.
When Do You Need to Convert JSON to TypeScript?
Typing a third-party API: The vendor's docs are out of date or non-existent. You hit the endpoint, copy the JSON response, paste it here, and have accurate types in 30 seconds.
Generating types from a mock fixture: Your team has JSON test fixtures — turn them into types so tests catch shape changes at compile time instead of runtime.
Migrating a JS codebase to TypeScript: Use real production responses to seed your initial type definitions. Refine them later; ship the migration this week.
Reverse-engineering an internal service: When the source service's OpenAPI spec is missing or outdated, the JSON it actually returns is the source of truth. Convert it directly into client types.
Why Use PDFFlare for JSON to TypeScript?
Named Nested Interfaces
Nested objects become their own named interfaces with smart defaults derived from property names — User, Post, Comment.
Smart Array Handling
Arrays infer their element type. Mixed-type arrays become proper TypeScript unions, not just `unknown[]`.
100% Browser-Based
Your JSON stays on your device. Safe for production responses, internal API contracts, or sensitive payloads.
No Signup Required
Unlike most JSON-to-types tools, PDFFlare has no account, no rate limits, no premium feature gates.
Frequently Asked Questions About JSON to TypeScript
Yes, completely free. PDFFlare's JSON to TypeScript tool runs entirely in your browser. No signup, no rate limits, no premium tier.
Each object gets its own TypeScript interface. The names are inferred from property names (singularized for arrays of objects), so you typically get sensible defaults like User, Post, Comment, etc.
PDFFlare emits a TypeScript union for the element type. For example, an array containing both strings and numbers becomes (string | number)[]. Empty arrays become unknown[] so you can refine the type yourself.
Yes. If a property name isn't a valid TypeScript identifier (contains hyphens, spaces, special characters, etc.), the tool wraps it in quotes — "my-field": string — so the output compiles without manual fixes.
The output uses standard `export interface` and `export type` declarations — pure TypeScript with no runtime dependencies. Review the generated names alongside your existing types. Inference describes only the sample: it cannot establish all optional fields or every possible API value.
It's a placeholder that's easy to find-and-replace with your domain name (User, ApiResponse, Post, etc.). Generic-but-unambiguous beats trying to guess what the JSON represents.
Not yet — each object literal in the JSON becomes its own interface, even if two objects have identical properties. quicktype.io does structural deduplication; PDFFlare's lightweight version doesn't. Review the output and consolidate identical interfaces if your project needs a smaller schema.
No. PDFFlare's JSON to TypeScript converter runs 100% in your browser — your sample data never leaves your device. Safe for production payloads, internal APIs, or anything sensitive.