[EDIT] Don’t use the script below, it uses a somewhat inaccurate source for determining the JLPT level of each kanji (specifically, it’s based off of the old JLPT 1…4 tests rather than the new N1…N5 tests. Sorry for making such a stupid mistake). Use my new script instead. [END EDIT]
I was bored so I made it a thing. JLPT Level should show up just underneath user synonyms. Uses KanjiDic2 for information, rather than Jisho. I thought this was the source that Jisho uses, but they appear to disagree occasionally (e.g. 米 is N3 according to Jisho, but N2 according to KanjiDic2).
I might end up making this into a more complete script later with various other bits of information (e.g. Japanese school grade, Mandarin reading).