Density tells you what you are looking at
Characters per token below three means the line is JSON, code, identifiers or non-Latin script. Those lines cost two to three times more per character than the prose around them.
The flag is the fastest way to find the one embedded object or base64 blob that is quietly responsible for half of a prompt.
What to do with a hot line
Minify it if it is JSON, convert it if it is a table, strip comments if it is code, or ask whether the model needs it at all. The prompt optimizer and data format optimizer handle the first two mechanically.
The counts here are estimated from character length so many lines profile instantly. Confirm anything you act on in the token counter.