{"id":131,"date":"2026-05-26T19:13:08","date_gmt":"2026-05-26T19:13:08","guid":{"rendered":"https:\/\/json-beautifier.org\/blog\/?p=131"},"modified":"2026-05-26T19:13:09","modified_gmt":"2026-05-26T19:13:09","slug":"fix-invalid-json-common-errors","status":"publish","type":"post","link":"https:\/\/json-beautifier.org\/blog\/fix-invalid-json-common-errors\/","title":{"rendered":"How to Fix Invalid JSON: 10 Common Errors Every Developer Hits (With Real Examples)"},"content":{"rendered":"\n

You’ve spent twenty minutes staring at a JSON file. Your API call keeps failing. The error message is some cryptic nonsense about “unexpected token.” And the JSON looks<\/em> fine to you.<\/p>\n\n\n\n

We’ve all been there.<\/p>\n\n\n\n

JSON is a strict format. That strictness is what makes it reliable across every programming language on Earth – but it’s also what turns a missing comma into a debugging nightmare. The good news? Almost every broken JSON file fails for one of the same ten reasons. Once you know what to look for, you can spot the problem in seconds.<\/p>\n\n\n\n

This guide covers all ten, with real examples of broken JSON and exactly how to fix each one. Bookmark it – you’ll come back.<\/p>\n\n\n\n

Quick tip before we start:<\/strong> the fastest way to find any JSON error is to paste it into a JSON validator<\/a>. A good one highlights the exact line and character where things go wrong, which saves a ton of squinting. But understanding why<\/em> each error happens means you’ll write better JSON from now on – so let’s go through them.<\/p>\n\n\n\n

1. Trailing Commas<\/h2>\n\n\n\n

This is the #1 mistake we see, and it’s almost always the culprit when JavaScript developers move from objects to JSON.<\/p>\n\n\n\n

Broken:<\/strong><\/p>\n\n\n\n

{\n  \"name\": \"Alice\",\n  \"age\": 30,\n}<\/code><\/pre>\n\n\n\n
That comma after 30 is illegal in JSON. JavaScript allows it. Python dicts allow it. JSON does not.<\/p>\n\n\n\n
Fix:<\/strong><\/p>\n\n\n\n
json\n{\n  \"name\": \"Alice\",\n  \"age\": 30\n}<\/code><\/pre>\n\n\n\n
Why this trips people up:<\/strong> Modern languages forgive trailing commas because they make diffs cleaner. JSON predates that convention, and the spec hasn’t budged.<\/p>\n\n\n\n
Pro tip:<\/strong> When you reorder properties in an object, the new last property gets a comma it shouldn’t have. Always check the bottom of your object after any edit.<\/p>\n\n\n\n
2. Single Quotes Instead of Double Quotes<\/h2>\n\n\n\n
Broken:<\/strong><\/p>\n\n\n\n
{\n  'name': 'Alice'\n}<\/code><\/pre>\n\n\n\n
Fix:<\/strong><\/p>\n\n\n\n
json\n{\n  \"name\": \"Alice\"\n}<\/code><\/pre>\n\n\n\n
JSON only accepts double quotes \u2014 for both keys and values. No exceptions.<\/p>\n\n\n\n
Why this trips people up:<\/strong> Python’s default repr uses single quotes. Copy a dict from a Python console, paste it into a JSON file, and every quote is wrong. Same story with JavaScript object literals.<\/p>\n\n\n\n
Pro tip:<\/strong> If you’re exporting JSON from Python, always use json.dumps(), never str(). Don’t hand-convert.<\/p>\n\n\n\n
3. Unquoted Keys<\/h2>\n\n\n\n
Broken:<\/strong><\/p>\n\n\n\n
json\n{\n\u00a0\u00a0name: \"Alice\"\n}<\/code><\/pre>\n\n\n\n
Fix:<\/strong><\/p>\n\n\n\n
json\n{\n\u00a0\u00a0\"name\": \"Alice\"\n}<\/code><\/pre>\n\n\n\n
JSON requires every key to be a string wrapped in double quotes. JavaScript lets you skip the quotes on simple keys. JSON does not.<\/p>\n\n\n\n
This is usually a dead giveaway that someone copy-pasted a JavaScript object and called it JSON. They’re related but they’re not the same thing.<\/p>\n\n\n\n
4. Missing Commas Between Properties<\/h2>\n\n\n\n
Broken:<\/strong><\/p>\n\n\n\n
json\n{\n\u00a0\u00a0\"name\": \"Alice\"\n\u00a0\u00a0\"age\": 30\n}<\/code><\/pre>\n\n\n\n
Fix:<\/strong><\/p>\n\n\n\n
json\n{\n\u00a0\u00a0\"name\": \"Alice\",\n\u00a0\u00a0\"age\": 30\n}<\/code><\/pre>\n\n\n\n
Every property pair (except the last) needs a comma after it.<\/p>\n\n\n\n
Why this one’s painful:<\/strong> the error message usually points to the next<\/em> line, not the line missing the comma. So you’ll see “unexpected token at line 4” when the actual problem is on line 3. Always check the line above the one the error points to.<\/p>\n\n\n\n
5. Comments<\/h2>\n\n\n\n
Broken:<\/strong><\/p>\n\n\n\n
json\n{\n\u00a0\u00a0\/\/ This is the user object\n\u00a0\u00a0\"name\": \"Alice\"\n}<\/code><\/pre>\n\n\n\n
Fix:<\/strong><\/p>\n\n\n\n
json\n{\n\u00a0\u00a0\"name\": \"Alice\"\n}<\/code><\/pre>\n\n\n\n
JSON has no concept of comments. Not \/\/, not \/* *\/, not #. Nothing.<\/p>\n\n\n\n
Workaround:<\/strong> If you really need to document a JSON config, add a comment key:<\/p>\n\n\n\n
json\n{\n\u00a0\u00a0\"_comment\": \"This is the user object\",\n\u00a0\u00a0\"name\": \"Alice\"\n}<\/code><\/pre>\n\n\n\n
Or use JSONC (JSON with Comments) \u2014 but only if you control the parser and you know it supports it. Most don’t.<\/p>\n\n\n\n
6. Unescaped Special Characters<\/h2>\n\n\n\n
Broken:<\/strong><\/p>\n\n\n\n
json\n{\n\u00a0\u00a0\"path\": \"C:\\Users\\Alice\"\n}<\/code><\/pre>\n\n\n\n
The backslashes aren’t escaped, so the parser tries to interpret \\U and \\A as escape sequences. Same problem if you have a literal double quote inside a string value:<\/p>\n\n\n\n
json\n{\n\u00a0\u00a0\"quote\": \"She said \"hi\"\"\n}<\/code><\/pre>\n\n\n\n
Fix:<\/strong><\/p>\n\n\n\n
json\n{\n\u00a0\u00a0\"path\": \"C:\\\\Users\\\\Alice\",\n\u00a0\u00a0\"quote\": \"She said \\\"hi\\\"\"\n}<\/code><\/pre>\n\n\n\n
The escape sequences you’ll use most often in JSON: \\\\ (backslash), \\” (double quote), \\n (newline), \\t (tab), and \\uXXXX (unicode).<\/p>\n\n\n\n
7. Mismatched or Missing Brackets<\/h2>\n\n\n\n
Broken:<\/strong><\/p>\n\n\n\n
json\n{\n\u00a0\u00a0\"users\": [\n\u00a0\u00a0\u00a0\u00a0{\"name\": \"Alice\"},\n\u00a0\u00a0\u00a0\u00a0{\"name\": \"Bob\"\n\u00a0\u00a0]\n}<\/code><\/pre>\n\n\n\n
Bob’s object is missing its closing brace. Easy to miss in a big file.<\/p>\n\n\n\n
Fix:<\/strong><\/p>\n\n\n\n
json\n{\n\u00a0\u00a0\"users\": [\n\u00a0\u00a0\u00a0\u00a0{\"name\": \"Alice\"},\n\u00a0\u00a0\u00a0\u00a0{\"name\": \"Bob\"}\n\u00a0\u00a0]\n}<\/code><\/pre>\n\n\n\n
This is where a JSON beautifier<\/a> earns its keep. Properly indented JSON makes mismatched brackets visible immediately – what you can’t see in minified one-liner JSON jumps out the moment it’s formatted.<\/p>\n\n\n\n
8. Wrong Capitalization of true, false, and null<\/strong><\/h2>\n\n\n\n
Broken:<\/strong><\/p>\n\n\n\n
json\n{\n\u00a0\u00a0\"active\": True,\n\u00a0\u00a0\"deleted\": Null\n}<\/code><\/pre>\n\n\n\n
Fix:<\/strong><\/p>\n\n\n\n
json\n{\n\u00a0\u00a0\"active\": true,\n\u00a0\u00a0\"deleted\": null\n}<\/code><\/pre>\n\n\n\n
JSON is case-sensitive. true, false, and null are all lowercase. Always.<\/p>\n\n\n\n
Why this trips people up:<\/strong> Python uses True, False, None. C# uses True\/False. Copy-paste from either, and you’ve got a problem.<\/p>\n\n\n\n
9. Invalid Number Formats<\/h2>\n\n\n\n
JSON has strict rules about how numbers can be written, and several formats that look normal in code are actually invalid.<\/p>\n\n\n\n
Broken:<\/strong><\/p>\n\n\n\n
json\n{\n\u00a0\u00a0\"id\": 007,\n\u00a0\u00a0\"rate\": .5,\n\u00a0\u00a0\"balance\": 100.,\n\u00a0\u00a0\"code\": 0xFF\n}<\/code><\/pre>\n\n\n\n
Here’s what’s wrong with each one:<\/p>\n\n\n\n