JSON Validator

Check JSON syntax and get detailed error information.

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Input
Output
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About json validator

JSON Validator is one page doing one thing. No account, no settings to sync, no history building up somewhere.

There is no account and no upload step. Whatever you paste lives in a variable until you close the tab, and then it does not.

You will find it under JSON, alongside 25 other tools for the same sort of job.

Reports error line/column position and detected JSON type.

How to use it

01
Start it
Every control is on the tool itself. Keyboard shortcuts, where there are any, are listed beside it.
02
Watch it run
It updates in the page as you go. Nothing is sent anywhere, so it keeps working with the network off.
03
Close when done
Nothing is stored between visits. Reloading gives you a clean start rather than picking up where you left off.

Examples

Valid JSON
A well-formed JSON object passes validation
Input
{"name": "Alice", "age": 30, "active": true}
Output
Valid: yes
Type: object
Size: 3
Invalid JSON
A JSON string with a trailing comma fails validation
Input
{"name": "Alice", "age": 30,}
Output
{
  "valid": false,
  "error": "JSON Parse error: Property name must be a string literal"
}

Questions

Does JSON Validator work offline?+

Yes. It is JavaScript running in this tab, so once the page has loaded it needs nothing further from the network. Put the machine in flight mode and it carries on. Nothing you do here is sent anywhere, because there is nowhere for it to go.

Does it remember anything between visits?+

No. Reload the page and it starts from nothing. There is no account, no saved state and no cookie holding your last session. That is a deliberate trade: it cannot lose your data because it never keeps any.

Is it accurate?+

Timing comes from performance.now(), the high resolution clock the browser provides, rather than from setInterval, which drifts by a few milliseconds every tick and compounds over minutes. What can still shift things is the browser throttling a tab in the background, so leave it visible if the timing matters.

Does it make a sound?+

Where a sound makes sense, it is generated with the Web Audio API rather than loaded as a file, so there is nothing to download and nothing to block. Browsers refuse to start audio until you have interacted with the page, which is why the first press is what switches it on.

Can I use JSON Validator on a phone?+

Yes. The controls are sized for touch and the layout collapses to one column on a narrow screen. Bear in mind that a phone locking its screen will suspend the page, and timing stops with it.