What is the most common JSON error?

Trailing commas are the most common JSON error. JSON does not allow a comma after the last element in an array or object. Many programming languages allow trailing commas, so developers expect JSON to do the same.

Why does JavaScript allow trailing commas but JSON does not?

JSON is a strict data interchange format specified by RFC 8259. JavaScript is a programming language with more lenient syntax rules. JSON was designed to be simple and unambiguous, so trailing commas were excluded.

Can FixTools automatically fix my JSON?

FixTools identifies and explains errors. For common issues like trailing commas or single quotes, the fix is straightforward and you can correct it manually in the editor before revalidating.

What does "unexpected end of input" mean in JSON?

It means the JSON parser reached the end of the string before the structure was complete. Usually caused by a missing closing bracket } or ] or an unterminated string.

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Fix Invalid JSON

Invalid JSON can come from many sources: hand-editing a config file, copying from an API response that wrapped JSON in HTML, a template that left a trailing comma, or a serialiser that used single quotes. The most common JSON errors — and how to fix them — are:

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Trailing comma after last element — remove the final comma before ] or }

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Single quotes instead of double quotes — replace ' with " around strings and keys

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Unquoted keys — add double quotes around all property names

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How to use this tool

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Paste your invalid JSON and click Validate to get the exact error location and what needs to be fixed.

How It Works

Step-by-step guide to fix invalid json:

1
Paste the invalid JSON
Copy the JSON you need to fix and paste it into FixTools.
2
Read the error message
FixTools reports the line, column, and type of error. Common messages: "Unexpected token", "Expected comma", "Unexpected end of input".
3
Fix the error
Correct the issue at the reported location. Common fixes: add a missing comma, remove a trailing comma, replace single quotes with double quotes, or add quotes around a key.
4
Revalidate
Click Validate again. Repeat until the JSON shows as valid.