JSON to Code Converter — TypeScript, Go & Dart
Paste any JSON payload to generate strongly typed TypeScript interfaces, Go structs, or Dart classes. Runs 100% locally in your browser — zero bytes uploaded.
Geek check: open DevTools → Network tab — 0 bytes of your data uploaded.
Generated code will appear here.
Generate production-ready types in seconds
Hand-writing type definitions for large REST API responses or webhook payloads is tedious and prone to subtle type mismatch bugs. This converter inspects your sample JSON, determines exact primitive types, decomposes nested objects, and outputs clean, idiomatic models ready to paste directly into your project codebase.
Private by design for sensitive API data
Many online code generation services send your raw JSON payloads to external cloud servers for processing. When dealing with database dumps, user profile objects, or internal API tokens, sending payloads across third-party servers presents severe confidentiality risks. YuliusBox parses your JSON entirely in your browser window — you can verify in your browser DevTools Network tab that no network requests are dispatched during conversion.
Recursive AST type inference, language mapping & measured benchmarks
When you paste a JSON document into JsonConverterClient.tsx, the engine calls native JSON.parse() and recursively walks the resulting object graph to build a structural type map. Nested objects are extracted into named child declarations (converting snake_case or kebab-case keys into idiomatic PascalCase identifiers), arrays are inspected across all elements to infer homogeneous or union element types, and numbers are distinguished between integer (int in Go / Dart) and IEEE-754 floating-point (float64 / double) values.
How to verify zero-upload execution in Browser DevTools: Open DevTools (F12 → Network), clear the request log or switch to Offline mode, and paste a production JSON response. Zero network requests are made while switching between TypeScript, Go, and Dart output tabs.
| JSON Input / Payload Size | TypeScript Output | Go Struct Output | Dart Class Output | Measured Parse + Emit Time |
|---|---|---|---|---|
| Small REST Object (1.52 KiB / 5 items) | export interface Root { ... } | type Root struct { `json:"..."` } | class Root { fromJson / toJson } | 0.30 ms (4 interfaces) |
| Medium Webhook (27.45 KiB / 100 items) | Deduped child array interfaces | int vs float64 field inference | Null-safe ? field annotations | 0.10–0.40 ms |
| Large Dataset (273.99 KiB / 1,000 items) | Recursive nested object extraction | CamelCase exported struct fields | Typed List<T> map builders | 0.90 ms |
Dedicated Type Generator
JSON to TypeScript — Interface & Type Generator with Optional Fields Guide→Frequently asked questions
How does the tool infer types from sample JSON?
The parser inspects each key-value pair in your JSON payload. Numbers are typed as number (in TypeScript) or int/float64 (in Go) depending on whether they contain decimal fractions. Arrays are analyzed for homogeneous element types, and nested objects are recursively extracted into child interfaces or nested structs.
What is the difference between interface and type in TypeScript?
TypeScript interfaces support declaration merging and are traditionally preferred for object shape contracts and OOP inheritance. Type aliases are more flexible, supporting union types, primitives, tuples, and mapped types. For standard API responses, both work seamlessly.
Are my API payloads or JSON files uploaded to any server?
Never. All JSON parsing and code generation algorithms run 100% locally in your web browser using client-side JavaScript. Zero bytes of your data are transmitted over the network, making it completely safe for production API responses, tokens, and proprietary schemas.
How are nested objects handled in generated code?
Nested JSON objects are extracted into separate child interfaces or structs named with PascalCase derived from the property name. This keeps your generated code modular, readable, and reusable across multiple API client functions.
Does this tool support nullable or optional fields?
When a field contains null or empty values, the generator marks it as optional or nullable (e.g. string | null in TypeScript, or pointer/interface{} in Go). You can adjust optional flags directly in the generated output.
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