Show HN: A Fast JSON Formatter

2 weeks ago 1

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

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

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

npm install fast-json-format

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" // }

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

Run benchmarks yourself:

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

Size │ fast-json-format │ json-bigint │ JSON.stringify ─────────────┼──────────────────────┼──────────────────────┼───────────────────── 100 KB │ 1060 ops/sec │ 679 ops/sec │ 2394 ops/sec 1 MB │ 90 ops/sec │ 68 ops/sec │ 223 ops/sec 5 MB │ 15 ops/sec │ 13 ops/sec │ 48 ops/sec 10 MB │ 7 ops/sec │ 6 ops/sec │ 23 ops/sec

MIT License - Copyright (c) Bruno Software Inc.

Issues and pull requests are welcome on the project repository.

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