I built a browser-only JSON to TypeScript Interface Generator — nested objects, arrays, options, 86 tests

When integrating a new API, the first thing I do is convert the JSON response to TypeScript interfaces. I built a free, browser-only JSON to TypeScript Interface Generator that handles nested objects, arrays, null, and union types. 👉 https://devnestio.pages.dev/json-to-typescript/ Auto-detect types — string, number, boolean, null, nested object interfaces, T[] arrays Nested interfaces — generates sub-interfaces for nested objects automatically Array handling — infers item type from first elemen
When integrating a new API, the first thing I do is convert the JSON response to TypeScript interfaces. I built a free, browser-only JSON to TypeScript Interface Generator that handles nested objects, arrays, null, and union types.
Live Tool
👉 https://devnestio.pages.dev/json-to-typescript/
What it does
-
Auto-detect types —
string,number,boolean,null, nested object interfaces,T[]arrays - Nested interfaces — generates sub-interfaces for nested objects automatically
- Array handling — infers item type from first element, creates type alias for root arrays
-
Options — optional (
?), readonly, export, semicolons on/off -
Root name — configurable (default:
Root) - Syntax highlighting — keywords in purple, interfaces in blue, types in green
- Auto-convert — updates output 400ms after typing
- Example presets — User, API Response, Config, Array, Deeply Nested
- 100% client-side — runs entirely in your browser
Example conversion
Input JSON:
{
"id": 42,
"name": "Alice",
"active": true,
"score": 98.6,
"address": null,
"tags": ["admin"],
"profile": {
"avatar": "url",
"bio": "Developer"
}
}
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Generated TypeScript:
export interface Profile {
avatar: string;
bio: string;
}
export interface Root {
id: number;
name: string;
active: boolean;
score: number;
address: null;
tags: string[];
profile: Profile;
}
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Type inference rules
| JSON value | TypeScript type |
|---|---|
"hello" |
string |
42, 3.14
|
number |
true/false
|
boolean |
null |
null |
[...] |
ItemType[] |
{} |
Generated interface |
[] (empty) |
unknown[] |
Testing
86 tests, all passing ✅
Tests cover:
- Type inference for all primitive types
- Nested object → sub-interface generation
- Array type inference
- Empty array →
unknown[] - Root array → type alias
- All option combinations (optional, readonly, export, semicolons)
- Auto-convert debounce
- Syntax highlighting classes
- Example preset loading
- Format JSON button
- Error handling for invalid JSON
All tools at devnestio.pages.dev.



