JSON → code generator
Paste a JSON object or array and generate ready-to-use type definitions for your language of choice — no setup required.
About this tool
Hand-writing type definitions from a sample API response is dull, mechanical, and exactly the kind of work where mistakes hide. Miss an optional field and you get a runtime error weeks later; misread a nested array's shape and the compiler happily agrees with you until production disagrees. Generating types from a real payload removes that class of error and gets you an accurate starting point in seconds. What generation cannot do is infer intent. A JSON sample shows what one response contained, not what the API contract permits: a field that happened to be null in the sample might be an optional string, a number that happened to be integral might be a float, and an empty array reveals nothing about its element type. Generated types are a first draft to be corrected against the API documentation, not a substitute for it. This tool converts a pasted JSON object or array into TypeScript interfaces, Python dataclasses, Go structs, Rust structs, Java records, or Zod schemas, handling nested objects and arrays. It runs in your browser, so payloads containing real data stay local.
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Paste a JSON object or array into the input field.
- 2
Select the target language: TypeScript, Python, Go, Java, Rust, or others.
- 3
The generated type definitions or structs appear instantly.
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Click Copy to paste the generated code directly into your project.
Generate TypeScript interfaces from an API response to add static typing to your frontend.
Convert a JSON config into a Python dataclass for cleaner, type-safe configuration handling.
Turn a JSON payload into a Go struct with json tags for use in a REST API handler.
JSON to TypeScript interface
{"id":1,"name":"Alice","active":true}interface Root {
id: number;
name: string;
active: boolean;
}JSON to Python dataclass
{"id":1,"name":"Alice"}@dataclass
class Root:
id: int
name: strEvery field is generated as required
Cause: A single sample cannot show optionality. If a field is present in the payload, the generator has no way to know the API sometimes omits it.
Fix: Mark fields optional by hand against the API documentation, or generate from several samples that exercise different response shapes. In TypeScript, be aware that a field which is sometimes absent needs ? rather than a union with undefined.
A null value produces a useless type
Cause: null carries no type information. The generator can only emit null, any, or a nullable unknown, none of which is what you want.
Fix: Replace nulls in your sample with representative values before generating, then widen the type to include null afterwards. This is where a sample from the documentation beats one captured from a live call.
Large integers or monetary values lose precision
Cause: JSON numbers have no declared type, and JavaScript parses them as doubles. IDs beyond about nine quadrillion and high-precision decimals are already rounded before the generator sees them.
Fix: Type large identifiers as strings and monetary values as a decimal type appropriate to your language, not as float or number. Many APIs deliberately return large IDs as strings for exactly this reason.
These answers explain common json → code tasks, expected input formats, and edge cases so both visitors and search engines can understand what this tool does.
Which languages does this tool support?
TypeScript (interface), Python (dataclass), Go (struct with json tags), Rust (struct with serde derives), Java (record), and Zod schema. Select the target language with the tabs above the output.
Does it handle nested objects?
Yes. Nested objects are recursively expanded into separate named types or structs. The root type is named Root and nested types use the field name as the type name in PascalCase.
What happens if the JSON contains an array?
Arrays are typed as typed slices, lists, or arrays in each language. If the array contains objects, the element type is inferred from the first element.
Does this work for API response bodies?
Yes. Copy the JSON response from your browser's Network tab or from a curl response, paste it here, pick your language, and you get a complete type definition ready to paste into your project.
Are null values handled?
Null fields are typed as nullable or optional in each language — Optional in Python, *Type pointers in Go, Option<T> in Rust, and null union members in TypeScript.