Malformed JSON with a trailing comma

Handle it in code

Each snippet below was run against this exact file with Python 3.14.4 and Node 24.15.0 when this page was built, and the output shown is what it printed.

Python

Report where the error is. A line and column turn "invalid file" into something a user can fix.

import json

try:
    with open("malformed-trailing-comma.json", encoding="utf-8") as f:
        json.load(f)
    print("valid")
except json.JSONDecodeError as e:
    print(f"invalid JSON at line {e.lineno}, column {e.colno}: {e.msg}")

Run against this file, it prints: invalid JSON at line 3, column 9: Illegal trailing comma before end of object

Node.js

The error message includes the position in recent Node versions.

const fs = require('node:fs');

try {
  JSON.parse(fs.readFileSync('malformed-trailing-comma.json', 'utf8'));
  console.log('valid');
} catch (e) {
  console.log('invalid JSON:', e.message);
}

Run against this file, it prints: invalid JSON: Expected double-quoted property name in JSON at position 22 (line 4 column 1)