How to Format JSON in JavaScript

Basic JSON Formatting with JSON.stringify

JavaScript's built-in JSON.stringify(value, replacer, space) formats JSON. The third argument (space) controls indentation.

const data = { name: "Alice", age: 30, city: "Paris" };

// 2-space indentation (standard)
console.log(JSON.stringify(data, null, 2));

// 4-space indentation
console.log(JSON.stringify(data, null, 4));

// Tab indentation
console.log(JSON.stringify(data, null, "\t"));

Format a JSON String (parse then format)

const jsonString = '{"name":"Alice","age":30,"city":"Paris"}';

const data = JSON.parse(jsonString);
const formatted = JSON.stringify(data, null, 2);
console.log(formatted);

Format JSON in Node.js (read and write a file)

const fs = require('fs');

const raw = fs.readFileSync('data.json', 'utf8');
const data = JSON.parse(raw);
const formatted = JSON.stringify(data, null, 2);
fs.writeFileSync('data_formatted.json', formatted);

Format JSON for HTML Display

// Display formatted JSON in a 
 element
const pre = document.getElementById('output');
pre.textContent = JSON.stringify(data, null, 2);

    
Format JSON from the Command Line (Node.js one-liner)
    
# Pipe JSON through Node.js
echo '{"name":"Alice","age":30}' | node -e "
  let d=''; process.stdin.on('data',c=>d+=c);
  process.stdin.on('end',()=>console.log(JSON.stringify(JSON.parse(d),null,2)));
"

# Or use jq (recommended for CLI)
echo '{"name":"Alice","age":30}' | jq '.'

    
What does JSON.stringify(data, null, 2) mean?
    
The three arguments are:
    

      
data — the JavaScript object or array to serialize
      
null — the replacer: null means include all properties; you can pass an array of key names to filter
      
2 — the space: number of spaces per indent level, or a string like "\t" for tabs
    
  

Need to format JSON without writing code?

Paste any JSON into the free online formatter — instant results, no JavaScript environment needed.

Frequently Asked Questions