JSON to TypeScript
Infer TypeScript types from JSON.
This runs in your browser. Nothing is uploaded.
Drop a file here or choose oneChoose file
Infer types from a JSON example
JSON to TypeScript reads a JSON value and creates TypeScript declarations that describe its shape. An object becomes an interface or type, primitive values become TypeScript primitives, and nested objects become named declarations. The result is a useful starting point when an API response or fixture exists before a hand-written type does.
Paste an object, use the sample, or drop a JSON file into the input area. The page parses JSON first, so malformed syntax is reported before inference. The sample produces an interface that includes a name property, and the output can be copied or downloaded astypes.ts. Use JSON Formatter when you need to inspect the source independently.
What the generated declarations mean
An inferred declaration describes the values visible in the example, not every response your service might return. A property present in one fixture may be optional in production. A string may actually be a date, identifier, or constrained union. A number may represent a count, currency, timestamp, or another unit that the generator cannot know from JSON alone.
Arrays deserve the same review. A homogeneous list can produce a simple item type, while mixed items may need a union or a manually designed discriminated type. If null appears in a sample, check whether the field is nullable, optional, or both in the real contract.
Use the output as a starting point
After copying the declarations into a project, rename the root and nested types to match your domain. Add optional markers, literal unions, branded identifiers, documentation, and validation at the boundary where untrusted data enters your application. TypeScript declarations alone do not validate runtime JSON.
Compare a second representative response when the API has multiple shapes. The more complete the sample set, the less manual correction the generated output needs. For related structured data work, JSON to YAML andJSON to XML convert the same parsed kind of input for different receiving systems.
Local processing and review
Parsing, type inference, file reading, and downloading happen in your browser. Nothing is uploaded. Inspect the generated declarations before committing them, especially when the input includes private fields or values that should not appear in source control. The tool is an inference aid, not a schema registry or a substitute for runtime validation.
FAQ
Does JSON to TypeScript upload my data?
No. JSON is parsed and types are inferred in your browser. After the page loads, it still works in airplane mode. TheDevTab never receives the JSON.
What JSON shape should I provide?
Provide a representative JSON object or array. The output uses its keys, values, and nested structures to infer interfaces and property types.
Does the output validate my API schema?
No. The generated interfaces describe the example you supplied. They do not prove that future API responses contain the same fields or types.
How are arrays handled?
Arrays are inferred from their items. A mixed array may need manual review because a sample cannot always express every valid union or optional case.
What about null values?
Null is preserved as a nullable type where the inference engine can identify it. Review nullable and optional properties against the real contract before using the output.
Can I edit the generated TypeScript?
Yes. Copy or download the output, then refine names, optional properties, unions, and domain-specific constraints in your project.