Practical example
Generate types from samples where one record has id: 1 and another has id: null, then review whether the property should be nullable or optional.
JSON to TypeScript Interface Generator
Paste JSON and generate TypeScript interfaces or type aliases with nested objects, arrays, null values, optional fields, readonly properties, and semicolons.
Options
What is a JSON to TypeScript generator?
A JSON to TypeScript generator turns sample JSON data into TypeScript interfaces or type aliases that describe the shape of the object.
It helps when consuming API responses, documenting payloads, creating front-end models, or quickly drafting types before refining them in a codebase.
How to use the JSON to TypeScript generator
- Paste a JSON object, array, or API response into the input editor.
- Choose a root type name and whether to generate interfaces or type aliases.
- Enable readonly, optional fields, or semicolons if they match your project style.
- Click Generate types and copy the TypeScript output.
Tips
- Use representative JSON samples so optional fields and array item shapes are inferred more accurately.
- Fields missing from some objects in an array can be marked optional.
- Null values are represented as unions such as string | null.
- Review generated types before committing them to production code.
Type modeling checks
Interface versus type
Interfaces work well for object models that may be extended. Type aliases are useful for unions, primitives, and compact generated output.
Optional fields
If an API omits a field in some responses, keep it optional instead of forcing consumers to handle impossible required values.
Null and undefined
A field that is present with null is different from a missing field. Review generated unions before using the type in strict TypeScript projects.
Representative samples
Generate from realistic API examples with nested objects, arrays, empty values, and alternative item shapes.
Related guides
Learn the workflow behind this tool and what to check next.
API contracts
JSON Schema for reliable API contracts
A schema workflow that treats successful and failing payloads as executable documentation rather than relying on one ideal sample.
Read guide
APIs and data
How to debug JSON API payloads
A practical workflow for formatting JSON, finding syntax errors, validating payload shape, and checking response status when API data looks wrong.
Read guide
JSON-to-TypeScript checks before trusting generated types
Generated interfaces describe the sample you paste, not the full API contract, so optional fields, unions, nulls, and arrays need review.
Use representative samples
Generate types from payloads that include empty states, errors, nested objects, arrays, nullable values, and optional fields.
Mark nullable fields
Review null, missing values, and empty strings separately so the generated TypeScript reflects actual runtime behavior.
Review arrays and unions
Check arrays with mixed objects, primitive values, and empty lists before accepting inferred unions or overly narrow element types.
Align runtime validation
Use generated types with schema validation or API tests when data comes from external services or user-controlled sources.
A practical example, an edge case, and a maintainer note
Edge case
A sample cannot reveal every valid enum, union variant, or optional field, so generated types can be narrower than the real API.
Maintainer note
I treat generated interfaces as a starting draft and reconcile them with the API schema and production examples.
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JSON to TypeScript Generator FAQ
Does it support nested objects?
Yes. Nested objects are emitted as separate named interfaces or type aliases.
How are arrays handled?
Arrays are inferred from their items. Arrays of objects are merged into a shared item type, with missing fields handled as optional or undefined.
Can it generate type aliases instead of interfaces?
Yes. Use the declaration style control to switch between interfaces and type aliases.
Is my JSON uploaded?
No. Type generation runs in your browser.