fast-json-format

A blazing fast JSON formatting library that pretty-prints JSON like strings

Why?

JSON.stringify(JSON.parse(str), null, 2) is fast — but it’s also lossy and strict:

• ❌ Breaks on BigInt: 12345678901234567890n, precision is lost.
• ⚙️ Loses numeric precision: 1.2300 becomes 1.23, zeroes are dropped.
• 🚫 Fails on imperfect JSON: Minor syntax issues in “JSON-like” strings can crash it.

fast-json-format aims to pretty-print without losing data or precision, while staying lightweight and forgiving.
It preserves BigInt literals, decimal formatting, and handles malformed input gracefully

Features

• 🔧 Handles invalid/malformed JSON gracefully
• 📦 Works with BigInt literals
• 🎨 Custom indentation support
• 🪶 Lightweight - single file, zero dependencies
• ✅ Thoroughly tested

Installation

npm install fast-json-format

Usage

Basic Usage

const fastJsonFormat = require('fast-json-format');

const minified = '{"name":"John","age":30,"city":"New York"}';
const formatted = fastJsonFormat(minified);

console.log(formatted);
// {
//   "name": "John",
//   "age": 30,
//   "city": "New York"
// }

Custom Indentation

// Use 4 spaces
const formatted = fastJsonFormat(jsonString, '    ');

Performance

Run benchmarks yourself:

npm run benchmark

JSON.stringify is inherently faster (as it’s native and C++-optimized) Performance improvements are welcome :)

Size         │ fast-json-format     │ json-bigint          │ lossless-json        │ JSON.stringify      
─────────────┼──────────────────────┼──────────────────────┼──────────────────────┼─────────────────────
100 KB       │ 1064 ops/sec         │ 712 ops/sec          │ 609 ops/sec          │ 2432 ops/sec        
1 MB         │ 91 ops/sec           │ 65 ops/sec           │ 43 ops/sec           │ 238 ops/sec         
5 MB         │ 15 ops/sec           │ 13 ops/sec           │ 6 ops/sec            │ 47 ops/sec          
10 MB        │ 7 ops/sec            │ 7 ops/sec            │ 3 ops/sec            │ 23 ops/sec              

Testing

npm test

License

MIT License - Copyright (c) Bruno Software Inc.

Contributing

Issues and pull requests are welcome on the project repository.