5 Common JSON Errors and How to Fix Them

Every developer has seen the dreaded "Unexpected token" or "JSON.parse error" message. JSON has strict syntax rules, and even a tiny mistake breaks the entire document. Here are the 5 most common errors and exactly how to fix each one.

Error 1: Trailing Commas

The most common JSON error. JavaScript allows trailing commas, but JSON does not.

❌ Invalid:

✅ Fixed:

Rule: The last item in an object or array must NOT have a comma after it.

Error 2: Single Quotes

JSON requires double quotes for all strings and keys. Single quotes are not valid.

❌ Invalid:

✅ Fixed:

Rule: Always use double quotes (") for both keys and string values. Never single quotes (').

Error 3: Unquoted Keys

In JavaScript objects, keys don't need quotes. In JSON, they always do.

❌ Invalid:

✅ Fixed:

Rule: Every key in JSON must be a double-quoted string.

Error 4: Missing Commas

Forgetting a comma between properties is easy to do, especially in multi-line JSON.

❌ Invalid:

✅ Fixed:

Rule: Every key-value pair must be followed by a comma, except the last one.

Error 5: Unmatched Brackets

Opening a bracket or brace without closing it — or closing one that was never opened.

❌ Invalid:

✅ Fixed:

Rule: Every { needs a matching }, and every [ needs a matching ]. Use an editor with bracket matching to spot these quickly.

How to Fix JSON Automatically

Don't want to hunt for errors manually? Our Auto-Fix JSON tool detects and repairs all five of these errors automatically. Just paste your broken JSON and click "Fix" — the tool shows you exactly what it repaired.

You can also use our JSON Formatter & Validator to pinpoint the exact line and character where an error occurs, making manual fixes easy.

Prevention Tips

• Use an editor with JSON syntax highlighting (VS Code, Sublime Text)
• Enable auto-format on save in your IDE
• Validate JSON before sending it to an API
• Use TypeScript or schema validation to catch errors at compile time
• Never manually edit minified JSON — format it first, edit, then minify