Why an unquoted scalar is dangerous
In YAML, a scalar that is not quoted has its type inferred from how it looks. Write count: 3 and you get the integer three; write ratio: 1.5 and you get a float; write enabled: true and you get a boolean. This is convenient until the inference guesses wrong, and because the same text can be a string in one context and a typed value in another, the mistakes are easy to miss. The fix is always the same, quote the scalar, but you have to know which values need it.
The Norway problem
The most famous example is known as the Norway problem. In older YAML, the unquoted words yes, no, true, false, on, and off, in several capitalizations, are all booleans. So a list of country codes that includes Norway, written as a bare NO, silently becomes the boolean false. The same trap catches ON for Ontario and any field where a real string happens to spell a boolean keyword. YAML 1.2 narrowed the set of boolean spellings to just true and false, but a great deal of software still follows the older, broader YAML 1.1 rules, so the safe assumption is that bare no and yes are hazardous.
Numbers, versions, and leading zeros
Numeric coercion is just as sharp. A software version like 1.0 becomes the number one and loses its trailing zero, so 1.0 and 1.00 both collapse to the same value and the original text is gone. A US ZIP code or any identifier with a leading zero, such as 01234, can be read as a number and lose the zero, or be interpreted as octal in some parsers. A long numeric string like a phone number or an account number can exceed the safe integer range and be rounded. In every one of these cases the value should have been a string, and the only way to keep it one is to quote it.
How a converter stays safe
This is why converting JSON to YAML is not just a matter of changing the punctuation. Every JSON string that, written bare, would be read back as a boolean, a number, a null, or a date has to be emitted in quotes, or the YAML would mean something different from the JSON. A correct converter applies these quoting rules automatically, which is exactly what this tool does: a string stays a string. When you read its YAML output and see quotes around something like "NO" or "1.0", those quotes are not noise; they are the converter protecting the value from YAML's type guessing.