That is amazingly useful tool I didn’t know about until now, thank you.
Textise is similar and also doubles as a poor man’s text-only browser. https://www.textise.net/referrer
Both Marky and Textise work in some places where the other doesn’t.
Obviously you (or your LLM) can throw together JavaScript bookmarklets to convert whatever page you’re on. The tools’ homepages might have premade ones, I forget.