My caffeine tolerance is already extremely low thanks to my self-imposed restriction of only actively consuming caffeine a maximum of three times a week. For reference, one cup of coffee past noon will keep me awake into the early morning. A cup of tea past ~15:00 will have a noticeable impact on my ability to fall asleep.
My caffeine consumption the past two weeks has been very low. For reference, about two weeks without any caffeine is about how long it takes for tolerance to be lost.
Yesterday I had a cup of tea followed by an instant coffee (tea first for the possible benefits of theanine). I was jittering, my mind felt sharp, I was honed in, and I felt overheated. I’ve never had such a strong effect from caffeine before. Even with my low intake and care taken not to consume too much, I must have had a tolerance built up.