Common JSON Syntax Errors (and How to Fix Each One)
JSON has a small, strict grammar, which is why a single stray character can make a whole
document fail to parse with a vague message like Unexpected token. Below are the
errors that break JSON most often, each with an example and a fix. Paste any of these into the
jsonbloom editor and it will point to the exact line and column that failed.
Trailing comma
A comma after the last item is valid in JavaScript but not in JSON:
{ "a": 1, "b": 2, } // invalid
{ "a": 1, "b": 2 } // fix: remove the last commaMissing or wrong quotes (single vs double)
JSON strings must use double quotes. Single quotes are not allowed:
{ 'name': 'Ada' } // invalid
{ "name": "Ada" } // fix: use double quotesUnquoted keys
Every key must be a quoted string:
{ name: "Ada" } // invalid (this is JavaScript)
{ "name": "Ada" } // fix: quote the keyUnescaped special characters
Inside a string, double quotes, backslashes, and control characters must be escaped. A literal newline or an unescaped quote breaks the string:
{ "path": "C:\Users" } // fix: escape the backslash
{ "quote": "She said \"hi\"" } // fix: escape inner quotesMissing or mismatched brackets and braces
Every { needs a } and every [ needs a
]. When they do not match, the parser usually fails at the very end of the
document. The status bar's line and column tell you where it gave up — count opening vs closing
symbols from there.
Comments aren't allowed in JSON
{
// the API key <- invalid
"key": "abc"
}Remove comments, or use JSON5/JSONC if your tooling supports it.
Encoding & BOM issues
A file saved with a byte-order mark (BOM) or in a non-UTF-8 encoding can fail to parse even
though it looks correct. Save the file as UTF-8 without BOM. NaN,
Infinity, and undefined are also not valid JSON values — use a number,
a string, or null instead.
How to validate JSON quickly
The fastest check is to paste it into a validator that reports the exact failure position. Drop your JSON into the jsonbloom editor: valid JSON renders as a graph, and invalid JSON shows the line, column, and reason so you can fix it in seconds.
Frequently asked questions
Why do I get "Unexpected token" when parsing JSON?
It means the parser hit a character it did not expect at that position — often a trailing comma, a single quote, an unquoted key, or a missing bracket. The editor shows the exact line and column so you can jump to it.
Are comments allowed in JSON?
No. Standard JSON (RFC 8259) does not allow // or /* */ comments. Remove them, or use a superset like JSON5 or JSONC in tools that support it.
Can JSON keys be unquoted?
No. Every key in JSON must be a double-quoted string. { name: "Ada" } is JavaScript, not JSON.
Try it now
Paste your JSON into the editor and see the structure as an interactive graph — free, in your browser.