JSON to TypeScript converter
Infer TypeScript declarations from a JSON sample, including unions, optional properties and nested objects. Review the generated code before adopting it as an API contract.
Developer Tools
JSON to TypeScript converter
Infer TypeScript declarations from a JSON sample, including unions, optional properties and nested objects. Review the generated code before adopting it as an API contract.
Maximum 200 KiB UTF-8; nesting limit: 50 levels.
.ts
For an array or primitive root, interface mode emits a root type alias.
Types describe only the sample. Missing properties become optional; null remains explicit; empty arrays use unknown[]. This does not validate data at runtime.
02 / How to use it
About this tool
How to use this tool
Input
Paste valid JSON or load the synthetic example. Include representative variants of the structure you want to describe.
Options
Enter a valid root name, such as ApiResponse, and choose interface or type. Non-object roots use a type alias.
Result
Select Convert, review optional properties and unions, then copy or download the .ts file. Check it with your compiler.
Worked example
Worked example · JSON to TypeScript converter
The second record has active but the first does not, so active is optional. Both observed tag types appear in the union.
Input
[{"id":1,"tag":"x"},{"id":2,"tag":null,"active":true}]Result
export type ApiResponse = ({
active?: boolean;
id: number;
tag: null | string;
})[];Formats and limits
- Limits
- Maximum 200 KiB UTF-8; nesting limit: 50 levels.
- Options
- Both describe objects. Type emits an alias; interface emits an interface for an object root. An array or primitive root requires an alias even in interface mode.
- Result
- All objects in the same array are compared. A property missing from any object is marked with ?. A null value is different from an absent property.
Common issues
What happens to null and empty arrays?
Null remains an explicit type and may appear in a union. An empty array becomes unknown[] because there are no elements to infer from.
Does this validate data at runtime?
No. TypeScript checks types during development; these declarations do not inspect future API responses. Add a runtime validator when needed.
Review the result before using it
The second record has active but the first does not, so active is optional. Both observed tag types appear in the union.
Formats and limits
Maximum 200 KiB UTF-8; nesting limit: 50 levels. Processed in this browser. No data is uploaded or saved.
Frequently Asked Questions
Should I choose interface or type?
Both describe objects. Type emits an alias; interface emits an interface for an object root. An array or primitive root requires an alias even in interface mode.
How are optional properties detected?
All objects in the same array are compared. A property missing from any object is marked with ?. A null value is different from an absent property.
What happens to null and empty arrays?
Null remains an explicit type and may appear in a union. An empty array becomes unknown[] because there are no elements to infer from.
Does this validate data at runtime?
No. TypeScript checks types during development; these declarations do not inspect future API responses. Add a runtime validator when needed.
What if the sample is incomplete?
The result only knows the values provided. It does not discover future fields, business rules, dates or enums. Use varied samples and review the actual contract.