Figuring out where Underfull \hbox (badness) is hiding?

Question

Is there a way to figure out where in a paragraph I need to add a hyphen to eliminate an Underfull \hbox (badness) message other than trial and error? FWIW, my messages are never about (badness 10000)—they're (badness 1527) or (badness 5417) or whatever—my understanding is that the higher the number, the "worse" the error.

Answer 1

The underfull warning tells you you have a line somewhere in your document that does not have sufficient material to fill your paragraph box.

Unlike Overfull warning, to which you can add \overfullrule at your preamble and it will show which line is causing the problem, I believe there is no such command for underfull warning.

However, forcing a line break using \ can trigger an underfull warning. As for the number, underfull warning value ranged between 0-10000. While the value above 10000 is for overfull warning.

You can go to this post for reference, the answer by Will Robertson provides a script to show an underfull segment of your document. \underfullrule?

Hope it helps!