Fix JSON trailing comma
A trailing comma after the last element in a JSON object or array causes a parse error. JSON does not allow trailing commas.
Trailing commas are valid in modern JavaScript and many config formats, but **not** in JSON (RFC 8259). Parsers fail at the comma because they expect another key or value.
This is one of the most common copy-paste errors when moving from JS/TS or JSONC into strict JSON.
Common causes
- Comma after the final property in an object.
- Comma after the last element in an array.
- Editor “format on save” that matches JS style and keeps a trailing comma.
How to narrow it down
- The error often points at the comma or the closing `}` / `]`. Remove the comma only for the last element at that nesting level.
- If you have nested objects, check each level — fixing one trailing comma may reveal another.
Examples
{
"a": 1,
}Comma after 1 when it is the last key.
{
"a": 1
}No comma after the last property.
How to fix
- Delete the comma after the last element at the same brace depth as the error.
- Run your file through the JSON validator after each change.
- In teams, enforce JSON with CI or pre-commit hooks so trailing commas never reach production.
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