How to Format Large JSON Files

Choose the Right Tool by File Size

jq — The Best CLI Tool for Large JSON

jq is a lightweight, fast JSON processor for the command line. It handles multi-gigabyte files without loading everything into memory at once.

# Install
brew install jq          # macOS
sudo apt install jq      # Ubuntu/Debian
winget install jqlang.jq # Windows

# Pretty-print a JSON file
jq . large.json

# Save formatted output
jq . large.json > formatted.json

# Compact (minify)
jq -c . large.json > minified.json

# Extract a nested field
jq '.users[0].name' large.json

# Count array items
jq '.users | length' large.json

# Format and validate (exit code 0 = valid)
jq empty large.json && echo "Valid JSON"

Python — Built-in json.tool

# Format in place (overwrites file)
python3 -m json.tool large.json > formatted.json

# With custom indentation
python3 -m json.tool --indent 4 large.json

# Validate only (no output)
python3 -m json.tool large.json > /dev/null && echo "Valid"

# Python script for more control
import json

with open("large.json", "r") as f:
    data = json.load(f)

with open("formatted.json", "w") as f:
    json.dump(data, f, indent=2, sort_keys=True)

Node.js — One-liner

# Format a JSON file using Node.js
node -e "
const fs = require('fs');
const data = JSON.parse(fs.readFileSync('large.json', 'utf8'));
fs.writeFileSync('formatted.json', JSON.stringify(data, null, 2));
console.log('Done');
"

# One-liner (pipe)
cat large.json | node -e "
process.stdin.resume();
let d='';
process.stdin.on('data',c=>d+=c);
process.stdin.on('end',()=>console.log(JSON.stringify(JSON.parse(d),null,2)));
" > formatted.json

VS Code — Format Document

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