🔴 Syntax Error Detection
Free JSON Validator
for Windows
Catch JSON syntax errors instantly. JSONLab pinpoints the exact line and character position of every mistake — no guessing, no browser needed.
Catch JSON syntax errors instantly. JSONLab pinpoints the exact line and character position of every mistake — no guessing, no browser needed.
JSONLab validates your JSON against the full RFC 8259 specification and reports errors with clear, human-readable messages. Here's an example of invalid JSON and how JSONLab reports it:
{
"name": "Alice",
"age": 30,
"tags": ["dev", "admin",]
"active": true
}
After you fix the error, JSONLab shows a clean confirmation:
| Error Type | Example (invalid) | Fix |
|---|---|---|
| Trailing comma | {"a": 1,} |
Remove the comma before } |
| Single quotes | {'key': 'value'} |
Use double quotes: "key" |
| Unquoted key | {key: "value"} |
Quote the key: "key" |
| Missing comma | {"a": 1 "b": 2} |
Add comma: {"a": 1, "b": 2} |
| Comment in JSON | // comment |
Remove — comments are not valid JSON |
| Undefined / NaN | {"val": undefined} |
Use null instead |
| Unclosed bracket | [1, 2, 3 |
Add closing ] |
Open a new tab in JSONLab and paste the JSON you want to validate. Or import a .json file from disk.
JSONLab validates as you type. If the JSON is invalid, the error banner appears immediately — no need to press a button.
The error message shows the exact line and character position. Scroll to that position in the editor to see the highlighted problem.
Correct the error — JSONLab will instantly confirm "Valid JSON" once the syntax is clean.
{} or a top-level array []. JSONLab correctly validates both forms.JSONLab finds JSON errors instantly, with the exact line number. Free for Windows.
