Free JSON to TypeScript
Generate TypeScript interfaces from JSON.
What is the JSON to TypeScript?
When you consume an API, the data arrives untyped — and hand-writing TypeScript interfaces to match it is tedious, easy to get wrong, and drifts out of date the moment the payload changes. Yet those types are exactly what give you autocomplete and catch mistakes at compile time.
This JSON to TypeScript converter reads a sample payload and generates matching interfaces, so you can type an API response in seconds instead of transcribing it by hand.
Last updated: Aug 13, 2026
What does this tool do?
You paste a JSON sample and the tool walks its structure, inferring a TypeScript interface for each object it finds.
It types primitives, nests interfaces for nested objects, turns arrays into typed arrays, and — for arrays of objects — merges keys and marks any that are missing from some items as optional.
Key features
Interface generation
Turns objects into named interfaces.
Nested types
Handles objects within objects.
Array merging
Unifies keys across arrays of objects.
Optional keys
Marks keys missing from some items with ?.
Private
Runs in your browser — nothing uploaded.
Example
Common use cases
- Frontend developers — Type API responses quickly.
- Backend developers — Generate DTOs from sample payloads.
- Full-stack developers — Keep client types in sync with data.
- API consumers — Add types to a third-party response.
- Students — Learn how TypeScript types map to JSON.
- Code reviewers — Draft types to compare against.
- Prototypers — Move fast with typed mock data.
- Anyone with JSON — Skip writing interfaces by hand.
Benefits
- It saves tedious hand-transcription of types.
- It handles nesting and arrays automatically.
- It flags optional fields you might miss.
- It keeps your data private in the browser.
Tips
- Paste a representative sample so all fields appear.
- Include array items with every possible key for accurate optionals.
- Rename the generated Root interface to something meaningful.
- Review inferred types — nulls and empty arrays can't be fully inferred.
- For unions, provide samples that show each variant.
- Consider a runtime validator (like Zod) alongside static types.
- Regenerate when the API payload changes.
- Watch for numbers that should really be string enums or IDs.
Common mistakes to avoid
Sampling a partial payload
Fix: Use a complete example so every field is represented in the types.
Trusting null/empty inference
Fix: null and [] can't reveal their real type — refine those manually.
Keeping the generic Root name
Fix: Rename interfaces to match your domain for readable code.
Assuming types validate at runtime
Fix: TypeScript is compile-time only; add a runtime validator if you need guarantees.
How it works
- 1
Paste JSON
A representative sample object.
- 2
Generate
It infers interfaces from the structure.
- 3
Copy the types
Drop them straight into your code.
Frequently asked questions
It merges the keys across all objects in the array; keys missing from some items are marked optional with a question mark.
It infers string, number, boolean, null, nested interfaces and arrays from your sample. Provide representative data for the best result.
It merges keys across every object in the array; keys missing from some items are marked optional with a question mark.
It infers string, number, boolean, null, nested interfaces and arrays from your sample — provide representative data for the best result.
Only loosely — null becomes null and an empty array becomes unknown[]. Refine those by hand.
No. TypeScript types are erased at compile time; use a runtime validator if you need to check data.
Yes — it recurses through nested objects and arrays, creating an interface for each object shape.
No. Generation happens entirely in your browser.
Conclusion
A JSON to TypeScript converter turns a sample payload into ready-to-use interfaces, giving you type safety without the busywork. Pair it with the JSON formatter to tidy the input first.