When working with JSON, it's important to be aware of certain syntax rules that are stricter than those of JavaScript objects. Many common mistakes can lead to errors when parsing or stringifying JSON data. One frequent issue is the use of trailing commas. In JavaScript, you might write an object or array with a comma after the last item, but in JSON, this is not allowed. For example, writing {"name": "Alice",} or ["apple", "banana", ] will cause a syntax error in JSON. Always make sure there are no extra commas at the end of your lists or objects.

Another typical mistake involves the use of single quotes. Unlike JavaScript, which allows single or double quotes for strings and keys, JSON requires double quotes for both keys and string values. Writing {'name': 'Alice'} is invalid in JSON; you must use {"name": "Alice"} instead. Additionally, JSON keys must always be strings enclosed in double quotes, and you cannot use variables or unquoted words as keys.

JSON supports numbers, strings, arrays, objects, booleans, and null values, but it does not allow comments, functions, or undefined values. Arrays and objects can be nested, but every string must be wrapped in double quotes. Remember that whitespace is allowed for readability, but it does not affect the data.

To avoid these common mistakes, always double-check your JSON for:

• Double quotes around all keys and string values;
• No trailing commas after the last element in arrays or objects;
• No comments or functions inside JSON data;
• Only supported value types: strings, numbers, objects, arrays, booleans, and null.