Use the free JSON to TypeScript Types below: your data never leaves your browser — all work happens on your device, and nothing is uploaded to any server.
Turn JSON Into TypeScript Interfaces in Seconds
Every developer who works with an API knows this chore: you fetch a response, you get a chunk of JSON, and now you need TypeScript types for it. Writing those interfaces by hand is slow and error-prone. Miss one nested object, guess a field type wrong, and you spend the next hour chasing a type error that was really a typo. This free JSON to TypeScript converter does the tedious part instantly. Paste your JSON, press convert, and get clean interfaces you can copy straight into your project.
The tool handles the structures that make hand-writing painful. Nested objects become their own named interfaces, so an address object inside a user object becomes an Address interface referenced by the User interface, not a blob of inline types. Arrays of objects become typed arrays of the right interface, with the name taken from the singular form of the field, so a “tags” array of objects becomes Tag. Arrays of simple values become string[], number[], or boolean[] as appropriate. Null values become null, and empty arrays become unknown[], because with no example item, guessing a type would be dishonest.
Why Types Matter for JSON
TypeScript’s whole value is catching mistakes before your code runs. Without types, a mistyped field name like user.nam instead of user.name compiles fine and fails silently at runtime, showing a blank name on screen. With a generated interface, the compiler catches it immediately and points at the exact line. That safety compounds across a project: every API response typed once saves dozens of debugging sessions later, and new team members can read the interface to understand the data shape without digging through API documentation or sample responses.
Generated types also document your data. An interface is a contract that says: this is what the API returns, these fields exist, and these are their types. When the API changes, you regenerate the interface and the compiler shows you every place in your code that assumed the old shape. That is far better than discovering the change from a user reporting a broken page. Many teams keep generated interfaces in a dedicated types file and regenerate them whenever an API version changes.
How to Use the Output
Press Convert to TypeScript, and the output appears with one interface per object level. Copy it into a .ts file, or straight into your component. If your JSON has arrays of objects with different shapes, the tool types the array from its first item, so check that the first item is representative.
Common Pitfalls the Tool Avoids
Hand-written conversions have predictable failure modes. People flatten nested objects into any, which defeats the purpose of types. People type every number as number even when an integer-only field deserves a comment, or type every array as any[]. People forget that JSON keys are strings, so a field like “user-name” becomes an invalid identifier if copied directly. This tool sidesteps those traps: it never emits any for a known value, it preserves nesting as named interfaces, and it keeps your original key names intact in the interface, so user-name stays readable and the mapping to the JSON is obvious.
One honest limit: the tool infers types from one sample, and a sample cannot show what it does not contain. If a field is always a string in your sample but sometimes a number in production, the generated type will say string, and you will need to widen it to string | number by hand. For critical APIs, convert two or three different real responses and compare the outputs. The differences between them are exactly the fields that need union types or optional markers.
Where This Fits Your Workflow
Frontend developers use this tool when integrating a new API endpoint, when onboarding onto a project with undocumented responses, and when writing tests with realistic mock data, because a typed mock catches shape mistakes early. Backend developers use it to document what their own endpoints return, by feeding a sample response through the converter and pasting the result into the API docs. Students learning TypeScript use it to see how interfaces map to real data, which is more instructive than any textbook example.
Because the tool runs entirely in your browser, your JSON never leaves your device. That matters when the sample contains real user data, internal identifiers, or anything you would not paste into a random website. There is no account, no upload, and no server log of your data. Paste, convert, copy, and close the tab.
Frequently Asked Questions
Does it handle deeply nested JSON? Yes. Each nesting level becomes its own interface, and the output lists them all.
What happens with mixed-type arrays? The array is typed from its first item. If your array genuinely mixes types, widen the result to a union by hand.
Can I convert JSON with comments? No. JSON does not allow comments, so strip them first. The tool will report invalid JSON if any remain.
Paste your JSON, grab your interfaces, and get back to building.