How to Fix Invalid JSON

First, read the error properly

Parsers report a position, e.g. 'Unexpected token } in JSON at position 74' or a line/column pair. That position is where the parser gave up — the actual mistake is usually at or just before it. Paste the JSON into a formatter, jump to that spot, and the culprit is normally staring at you.

The usual suspects

In practice, these eight cause nearly every failure:

• Trailing comma — {"a": 1,} is invalid; JSON forbids a comma after the last item.
• Single quotes — strings and keys must use double quotes: 'name' fails, "name" works.
• Unquoted keys — {name: "x"} is a JavaScript object literal, not JSON.
• Comments — // and /* */ are not part of JSON at all.
• undefined and NaN — not valid JSON values; use null or a number.
• Smart quotes — copying from Word or chat apps swaps " for curly quotes the parser rejects.
• Truncated data — a cut-off response loses its closing brackets; the error points at the very end.
• Invisible characters — a BOM or non-breaking space at the start fails with an error at position 0.

Why JSON is stricter than JavaScript

JSON looks like a JavaScript object literal but is a separate, deliberately tiny specification. The strictness is the feature: any parser in any language accepts exactly the same documents, with no dialect drift. When you want the relaxed version for config files, that's a different format (JSON5 or JSONC) — and standard parsers will still reject it.

The fast fix workflow

Paste the JSON into the formatter below, read the error position, fix that one spot, and re-validate — repeat until it pretty-prints. For machine-generated JSON that fails repeatedly, fix the generator (usually string concatenation that should be a serializer call).