JSON to TypeScript Converter
Paste a JSON sample to instantly generate matching TypeScript interfaces, with nested objects, optional fields, and nullable fields inferred automatically. Free online developer tool.
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TypeScript Interfaces
Interface definitions will appear here...
Free JSON to TypeScript Converter
Paste a JSON sample to instantly generate matching TypeScript interface declarations. Nested objects become their own named interfaces, arrays become typed arrays, and fields that are missing or null in your sample are marked optional or nullable automatically.
How to Use It
Paste any JSON object or array into the input box, or click "Load Example" to see a sample run. The converter parses your JSON, infers a type shape from the values it finds, and generates one interface per object level — nested objects are pulled out into their own interface named after the parent property, so the output stays readable even for deeply nested payloads.
Example
Given {"name": "Ann", "age": 30, "tags": ["a","b"], "address": {"city": "NYC", "zip": null}}, the tool generates a RootAddress interface for the nested object plus a Rootinterface referencing it, with tags: string[] and zip: null reflecting exactly what was observed in the sample.
Common Use Cases
- Typing an API response quickly without hand-writing interfaces field by field.
- Bootstrapping types for a third-party webhook payload or config file.
- Checking at a glance which fields in a JSON sample are optional or nullable.
- Speeding up TypeScript migrations of existing JavaScript codebases that consume JSON.
FAQs
How are optional and nullable fields detected?
If you paste an array of objects, the tool merges the shape of every element — a property that's missing from at least one object becomes optional (?:), and a property that's evernull gets a | null union added to its type.
What happens if a field's type is inconsistent across samples?
When the same property holds genuinely conflicting types across an array of samples (say, a string in one object and a boolean in another), the field falls back to unknown rather than guessing an inaccurate union — you can then refine it by hand.
Is my JSON uploaded anywhere?
No — parsing and type generation happen entirely client-side in your browser. Nothing you paste is sent to a server.