JSON Validator

JSON error messages are famously unhelpful. "Unexpected token } in JSON at position 847" tells you where the parser gave up, which is often a line or two after the thing that is actually wrong, and says nothing about what to do next.

This shows the failure in context: the line and column, the surrounding lines with the offending one marked, and a caret under the exact character the parser stopped at. Seeing it in place is usually enough on its own.

Underneath that it lists the likely causes. A trailing comma before a closing brace, single quotes instead of double, an unquoted key, a comment, a NaN, or braces that do not balance — those six account for the overwhelming majority of invalid JSON, and each is checked for directly. The checks deliberately ignore anything inside a string, so a comma in a sentence or an apostrophe in a name is never reported as a problem.

When the document is valid you get more than a green tick: the number of objects, arrays and keys, and how deeply it nests. That is often the real question — whether the structure is what you expected, not merely whether it parses.

Everything runs in your browser. API responses and configuration files routinely contain keys, tokens and customer data, and none of it is transmitted, stored or logged here.