Lawyers know the Harvard Bluebook is the gold standard for citation form. The current version (the 19th) can be bought online. But that’s not the only option. The 1st through 15th editions are available online for free in PDF form.
I would not rely on an out-of-date Bluebook for an academic paper. But for most day-to-day purposes of practicing lawyers, a 1991 version is close enough. I have heretofore gone with much worse. Now I no longer have an excuse not to probe the infinite details of the Bluebook to improve my citation form. Darn.