newbie needs help with content optimization using keyword density

Hey everyone, total newbie here trying to get my head around SEO and content optimization. i'm building a small web tool and trying to use a keyword density checker for better content analysis and to refine my content, but i'm running into some weird issues.

The problem is, sometimes when i paste in longer text or articles, my checker just hangs or gives really inconsistent results. like, it'll show a super high density for a word that barely appears, or just kinda crash. i'm probably doing something wrong on my end, maybe with how i'm handling the text input or the parsing logic.

It's throwing up stuff like this:

Error: Max buffer size exceeded for text processing.
    at analyzeText(line 123)
    at processRequest(line 45)

i'm trying to figure out if there are common beginner mistakes when setting up keyword density and frequency checks for content optimization? any tips on handling large text inputs or common parsing issues would be super helpful. help a brother out please...