A comma promises another value
JSON objects and arrays use commas to separate items. After a parser reads a comma, it expects another property or value—not the closing bracket. So `{"name":"Mira",}` fails: the comma says another property should follow, but `}` ends the object instead. The same problem occurs in an array such as `[1, 2,]`.
That rule is part of JSON’s grammar: its formal syntax defines which sequences of characters count as valid data. A trailing comma may look harmless to a person because it can make lists easier to edit, but it leaves the sequence outside that grammar.
Why the failure can stop an application
A JSON parser typically reads the text in order, checking each token against the grammar. When it reaches a closing bracket where it expected another item, it reports a syntax error and may refuse to load the entire document. The application that needed the data—perhaps to display settings or process an API response—then has nothing usable to work with.
The error message may point to the closing bracket rather than the comma: that is where the parser discovers the sequence cannot continue as expected. Some languages accept trailing commas in their own code, and some tools offer JSON-like formats with extra conveniences. Strict JSON does not. When data must pass between different programs, that small restriction helps ensure they all interpret the same text the same way.
