1) Trailing commas
JSON does not allow a comma after the last item in an object or array.
{
"a": 1,
}
Fix: remove the last comma.
2) Single quotes
JSON strings must use double quotes, not single quotes.
{ 'name': 'Ada' }
Fix:
{ "name": "Ada" }
3) Unquoted keys
In JSON, object keys must be quoted.
{ name: "Ada" }
Fix:
{ "name": "Ada" }
4) Missing brackets/braces
Every { needs a } and every [ needs a ].
Quick tip
If you see an error like “Unexpected token … at position N”, try formatting the JSON first — it makes the mistake easier to spot.