Convert JSON payloads into clean, idiomatic TypeScript interfaces or type aliases with customizable optional fields. Runs 100% locally in your browser.
Geek check: open DevTools → Network tab — 0 bytes of your data uploaded.
Generated code will appear here.
Processed 100% locally in your browser — files never leave your device.
Paste your raw JSON object or API response into the input code editor on the left.
Select your preferred declaration style: “interface” for extensible object shapes, or “type alias” for functional types.
Optionally check “Optional (?)” if your payload fields may be missing or nullable in production.
Click “Convert” to inspect the generated code, then click “Copy Code” to paste directly into your TypeScript project.
TypeScript offers two primary ways to define object types: interfaces (interface User { ... }) and type aliases (type User = { ... }). While both behave identically for standard object structures, their ecosystem semantics differ.
Interfaces support declaration merging (multiple declarations of the same interface automatically combine) and OOP extends inheritance, making them standard for public libraries and domain entity models. Type aliases are more flexible, capable of expressing unions (string | number), intersections, tuples, and mapped types. This tool lets you switch between both with a single click.
Real-world backend APIs rarely guarantee that every field will always be present. A user profile might lack a middleName, or an audit record might omit deletedAt until soft deletion occurs.
Enabling the Optional (?) flag appends the ? modifier to all generated properties (e.g. email?: string). This ensures your TypeScript compiler with strictNullChecks enabled will force consumers to handle potential undefined values safely, preventing runtime Cannot read properties of undefined exceptions.
Instead of dumping deeply nested structures into awkward any types, our converter recursively analyzes nested objects and multidimensional arrays. It identifies primitive data types (string, number, boolean) and maintains clean PascalCase naming for nested structures.
Developer payloads frequently contain confidential schema details, proprietary database field names, or mock production data. Unlike cloud-based converters, YuliusBox parses your JSON completely in your browser's V8/SpiderMonkey engine. You can verify in DevTools that zero bytes are sent across the network.
For standard API response objects, either is fine. Use 'interface' if you want declaration merging or OOP class implementation. Use 'type alias' if you prefer functional composition or union types.
Nested objects are recursively typed with structured indentation. Arrays with uniform elements are typed as T[] (e.g. string[] or number[]), while empty or mixed arrays safely default to any[].
It adds a question mark to every property name (e.g. name?: string). This marks fields as optional, helping you satisfy TypeScript strict null-checking when working with partial API responses.
Never. All JSON parsing and code transformation executes locally in your browser memory using client-side JavaScript. Zero bytes of your data leave your computer.