Phrase that allows a person to see what is on the Marauder's Map. Told to Harry Potter by Fred and George Weasley
"When you want to open the map, say I solemnly swear I am up to no good; to close it, say mischief managed.
by LitTeacher June 27, 2015
“I solemnly swear I am up to no good”
by Billy & Bobby August 30, 2019
To sarcastically suggest that you are speaking the truth, although you and probably the other people know that you are lying.
Dave: Steve bruv, did you see that Man just jump 50 ft in to the air?
Steve: Nah!! Actually?
Dave: Yeah bruv, swear up.
Steve: Nah!! Actually?
Dave: Yeah bruv, swear up.
by abcdefg h May 22, 2014