Booming Blade 5e source from Sword Coast Adventurer’s Guide.
Booming blade 5e
Casting Time: 1 action
Range: 5 feet
Components: V, M (a weapon)
Duration: 1 round
How does d&d 5e booming blade work?
As part of this booming Blade 5e spell action used to cast spells, you should use a weapon, which is aimed at a creature within the spell’s range. Otherwise, the spell will fail a melee attack.
Hitting the target will suffer the normal impact of the attack and will also become a booming energy sheath until your next round begins. If the target moves willingly before then, the spell will cause 1d8 thunder damage and the spell will end.