Lettering norms
Letterers work to rules of thumb: about 25 to 35 words per panel is comfortable, a balloon over 35 words wants splitting, and a page carrying more than about 210 words starts to bury the art. Paste a script laid out with PAGE and PANEL headings and the tool reads it the way the script editor does: it counts only the words in balloons, captions and sound effects, and takes the page and panel counts from the headings. Paste plain text instead and every word counts, so paste just the readable text and give it a page or panel count. Either way it reports words per page and per panel against those bands, and a panel averaging more than 35 words marks the script as dense whatever the page total.
Bands: under 60 words per page is sparse, 60 to 150 comfortable, 151 to 210 dense, over 210 overloaded. Your script never leaves the browser.