im so sick of googling it and clicking on free stuff and what is "free" is actually a "free trial" and now they spam my inbox with bullshit i neither need nor want. i really just want to write up and document my code…

I was gonna recommend drawio because that's what I used back then, but there's a claude.md in their github 

Umbrello looks alright, I actually downloaded it to poke around it a bit and if you don't mind an UI that isn't super user-friendly it should do the trick.