This is the very best way to open a stuck jar lid – put a folded dish towel down on a counter top and turn the jar upside down and keeping the top flat to the counter, strongly tap the jar down on the towel a number of times. This breaks the suction seal and the jar will almost 100% of the time open.
It’s worked great for me for decades
Chuck Lindholm – The Reluctant Poet
Extra help for stubborn jar lids.