JSON Validator – Validate JSON Online & Find Errors

Input

Output

Ready

Ln 1, Col 1

Validate JSON and see exactly what is wrong

Paste JSON and it is checked instantly against the JSON standard (RFC 8259). If it is invalid you get the line and column, the line is highlighted in the editor, and a hint explains the likely cause in plain English. The sample above contains a few typical mistakes. Try Repair to fix them automatically.

How to use it

Paste your JSON into the Input panel or open a .json file.
Read the result: a green Valid JSON badge, or an error card with the line, column and a suggested fix.
Click Go to error to jump to the problem, or Try auto-repair to fix common mistakes.

What the validator checks

Strict syntax: double-quoted keys and strings, no trailing commas, no comments, valid escapes and numbers.
Exact locations: line and column for every error, consistent in every browser.
Plain-English hints: trailing commas, single quotes, unquoted keys, Python literals, missing commas and unclosed brackets are recognised.
Hidden problems: duplicate keys (only the last value survives) and integers too large to keep their precision in JavaScript.

The most common JSON errors

{"a": 1,}: trailing comma before } or ]
{'a': 1}: single quotes instead of double quotes
{a: 1}: unquoted key
{"a": True}: Python True/None instead of true/null
// comment: comments are not allowed in JSON
{"a": [1, 2}: mismatched or missing brackets

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All tools are free and run privately in your browser.

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JSON Validator FAQ

How do I check if JSON is valid?

Paste it into the input panel. The status bar immediately shows Valid JSON or Invalid JSON, and invalid JSON gets an error card with the exact line and column.

Why does my JSON fail with "Unexpected token"?

Usually because of a trailing comma, a single-quoted string, an unquoted key or a comment. The validator names the likely cause and highlights the line so you can fix it quickly.

Does the validator detect duplicate keys?

Yes. JSON.parse silently keeps the last value for a duplicated key, so the validator warns you about each duplicate and the line it is on.

Is my data uploaded to a server?

No. The JSON Validator runs entirely in your browser using JavaScript. Your data is never uploaded, logged or stored, and the tool keeps working offline after your first visit.