Count it against the limit that matters.

100 characters is the hard cap, and it is not the number that matters. Search results and most surfaces truncate a title around 60 characters, so a 92 character title is legal and half invisible. This tool marks both, and the 60 is the one to design against.

5000 characters, of which roughly the first 120 show before the more button. That first line is the only part most viewers read, so it has to work on its own rather than being the start of a sentence that finishes out of sight.

Because there are two different right answers. A person counts an emoji as one character. YouTube's field counts it as two, because it measures UTF-16 units. For plain text the two agree, and the moment you use an emoji or an accented letter they do not. Both are shown so a title that is legal by one count and rejected by the other is not a surprise.

No. The counting happens in your browser. There is no account, no network request and no analytics on the text. You can disconnect from the internet and the page still works.

The limit is 500 characters across all of them together, which is why this counts the whole comma separated list rather than each tag. Tags are a weak signal on YouTube now; a specific title and a description that says what the video is remain far more useful than filling the field.