About JSON to TypeScript Interface
This tool reads a JSON object or array and automatically generates matching TypeScript interface or type declarations — including nested objects as their own named interfaces, arrays typed correctly, and optional fields detected from inconsistent sample data. Paste an example API response and get ready-to-use types for your frontend code in seconds. All processing happens locally in your browser; your data is never uploaded to a server.
How Type Inference Works (and Its Limits)
This tool infers types purely from the JSON values you provide — it has no knowledge of your actual API's schema, so it can only be as accurate as the sample data you paste in. Nested objects become their own named interface, based on the property name that contains them. When an array contains objects with inconsistent fields (some items missing a property others have), that property is marked optional with ? rather than assumed required. If the same field holds different types across array items (e.g. a number in one item and a string in another), the tool generates a union type like string | number. For the most accurate result, paste a sample that's representative of the real range of data your API can return — including any fields that are sometimes null or missing.
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