JSON is everywhere — APIs, config files, package.json — and it breaks in the most annoying ways. Here are the 5 errors I see most often, and the fastest ways to find and fix them without installing anything.
1. Trailing commas
{ "name": "Sujal", "city": "Jaipur", } That comma after "Jaipur" kills the whole file. JSON does not allow trailing commas, period. Delete it.
2. Single quotes instead of double quotes
{ 'name': 'Sujal' } Looks fine, is not JSON. Keys AND string values must use double quotes:
{ "name": "Sujal" } 3. Unquoted keys
{ name: "Sujal" } Valid JavaScript object, invalid JSON. Quote every key.
4. Comments
{ // user details "name": "Sujal" } JSON has no comments. If you need them, use JSONC in your editor — but strip them before sending to an API.
5. NaN, Infinity, undefined
{ "score": NaN } These are JavaScript things, not JSON things. Use null or a number.
The fastest ways to validate
Browser console (zero setup): paste your JSON into JSON.parse('...'). The error message tells you the exact character position where it broke. That's usually enough.
Python (already on most machines):
echo '{"a":1,}' | python3 -m json.tool It pretty-prints valid JSON and points at the error for invalid JSON.
jq (if you live in the terminal):
echo '{"a":1}' | jq . Formatting: pick one style and stick to it
2-space indent is the most common. Tabs are fine too. What matters is consistency — mixed indentation makes diffs unreadable and code reviews painful.
A real before/after
Before:
{ 'users': [ { name: 'Amit', age: 24, }, { name: 'Priya', age: 29, }, ], } After:
{ "users": [ { "name": "Amit", "age": 24 }, { "name": "Priya", "age": 29 } ] } Four fixes: quotes, keys, trailing commas, and it's done.
I got tired of switching between five different sites for this kind of work, so I built BulkTextKit — 15 free text tools in the browser, including a JSON formatter/validator that points at the exact error. Pro (batch processing, presets, CSV export) is $9 until Oct 19: https://bulktextkit.gt.tc
