How to Validate JSON Online (Free, Find the Error)
A single misplaced comma or quote can break an entire JSON file, and the error message from your code often isn't helpful. A JSON validator checks your JSON against the rules and points to what's wrong. This guide shows how to validate JSON for free and fix the most common errors.
✅ Try the JSON Formatter & Validator now — freeOpen →Invalid JSON breaks API calls, config loading and data parsing. Validating it quickly pinpoints the exact problem, saving you from hunting through a wall of text — essential for anyone working with APIs, config files or data.
The rules JSON must follow
- Keys and string values use double quotes, never single quotes.
- No trailing comma after the last item in an object or array.
- Every { and [ needs a matching } and ].
- Quotes inside strings must be escaped with a backslash.
- No comments — standard JSON doesn't allow // or /* */.
How validating helps you fix it
The validator parses your JSON and, if it fails, flags where the problem is so you can jump straight to it. Once it validates cleanly, you know it will parse correctly in your code.
Beautifying at the same time makes the structure readable, so a missing bracket or misplaced comma is much easier to spot visually.
Step-by-step
Common mistakes to avoid
Pro tips
Frequently asked questions
How do I validate JSON?
Paste it into the JSON Formatter & Validator — it checks the syntax instantly and flags any errors so you can fix them.
What are the most common JSON errors?
Single quotes, trailing commas, missing brackets, unescaped quotes, and comments (which JSON doesn't allow).
Why is my JSON invalid?
Usually one of the common mistakes above. The validator points you to the spot so you can fix it fast.
Is it free and private?
Yes — free with no sign-up, and validation runs in your browser.
Does it also format JSON?
Yes — it beautifies and minifies too, which makes errors easier to spot while you validate.
A JSON validator instantly checks your JSON and pinpoints what's breaking it — a trailing comma, single quotes, a missing bracket. Fix the flagged issues, and you know it'll parse correctly in your code. Free, fast and private in your browser.