Not Spellsinger.
I remember these things:
His first “spell” was part of “A Visit from Saint Nicholas” where he teleports a bunch of bad guys up to a distant wall by quoting the poem.
There is a magician who is helping him who cringes everytime he makes up a spell by creating poetry, because of the intrinsic dangers of just making stuff up.
He gets a magic sword and, through poetry, gives it a mono-filament edge.
Never read that one. Ever. Not even close. I want to know what it is and who wrote it when someone finally IDs it...