JSON Formatter
Format, minify and validate JSON without changing large integers, number notation, key order or string escapes. Import files and locate syntax errors.
JSON to TypeScript types
Infer TypeScript types from JSON samples, including nested objects, optional properties, arrays, unions and null.
Types are inferred from this sample. Missing object properties become optional; empty arrays use unknown[].
Updates as you type or change an option
About this tool
Use representative response samples to draft a type for your application, then review it against the actual API contract.
How to use
Paste a representative JSON sample and choose a type name. Copy the generated export or download a .ts file. Array samples are combined: properties missing from some objects become optional and different value types form unions.
Empty arrays use unknown[] and empty objects use { [key: string]: unknown }. A sample cannot describe values it does not contain, so review the type against your API contract. Duplicate keys are rejected. Limits: 2 MiB, 30,000 values and 80 nested levels.
Common questions
Can a sample describe every possible response?
No. Types reflect only the supplied values. Missing properties across array samples become optional, and empty arrays become unknown[]. Runtime validation is not generated.
Is a generated number type safe for a very large JSON ID?
The generator labels JSON numeric values as number; it does not change how JavaScript parses them. Integers beyond JavaScript’s safe range can lose precision in your application. Use a string-based API representation or a parser that preserves large numbers, and review the generated type accordingly.
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