Question 1

What exactly counts as "invalid" JSON here — are trailing commas or single quotes allowed?

Accepted Answer

This validates against strict JSON (RFC 8259): double-quoted keys and strings only, no trailing commas after the last item in an object or array, no comments, and no unquoted keys. If your input is valid JavaScript but not valid JSON — a common source of confusion — it will fail here.

Question 2

My JSON looks correct to me but still fails validation — why?

Accepted Answer

The most common causes are a trailing comma after the last array or object item, single quotes instead of double quotes, an unescaped quote or backslash inside a string, or a duplicate object key (technically parseable, but a frequent source of silent bugs downstream). The error message points at the exact line and column so you can check that spot first.

Question 3

Does this check my JSON against a schema, like JSON Schema?

Accepted Answer

No — this checks only that the JSON is well-formed (syntactically valid), not that it matches any particular shape, required fields, or data types. Schema validation is a different, heavier problem; this tool answers "is this parseable at all," which is usually the first thing you need to know when debugging a broken payload.

Question 4

Does validating a large JSON file freeze the page?

Accepted Answer

No — like every tool here, inputs at or above 200KB are validated in a background Web Worker rather than on the main thread, so the tab stays responsive even while checking a multi-megabyte file.

JSON Validator

Precise Errors

Catches Common Mistakes

Local Processing

Frequently Asked Questions