Teenagers have a knack for inventing creative Friday night alibis, from wildly unbelievable falsehoods to slick and practiced white lies.

But tonight one seemingly strange excuse should hold up, says Kim Patton, young adult specialist at the Lawrence Public Library.

“If you hear your child say, ‘Mom, Dad, I’m going to a rock concert at the library,’ well, I can assure you it is a real event,” Patton says. “You can even stop by, though we encourage parents NOT to stay.”

In an unexpected fusion of Black Sabbath and the card catalog, the Lawrence Public Library is hosting a Battle of the Bands from 6 to Friday night for musicians in junior high and high school.

Josh Gaston, guitarist and lead singer for the ever-evolving Lawrence trio Swamp Hag, says he and his bandmates enjoy “just rockin’ it” at the library.

“It’s cool, people don’t expect it,” says Gaston, 19. “It sounds like a joke when you tell people. They’re like, ‘Isn’t the library supposed to be quiet?'”

Swamp Hag, which Gaston describes as “old-school heavy metal with a fresh twist,” has played the library event before.

“It’s pretty simple: The more bands, the bigger the crowd,” says Gaston, who will attend Drake University this fall. “But even small crowds are pretty enthusiastic.”

“Battle of the Bands” takes place four to five times per year at the library and caters to youth ages 11 to 18. In colder months, the event warms up the library auditorium. Tonight, however, bands will unleash their sound on the book repository’s west lawn.

Box Social members, from left, Kevin Winn, Mark Whittemore and Kevin Lawrence practice an acoustic set in the basement of Lawrence's home. The quartet (drummer Chris Luckey is not pictured) of newly minted high school graduates will headline the Battle of the Bands at the Lawrence Public Library, 707 Vt.

Four groups are scheduled to play the literary-friendly event. Swamp Hag will be joined by local bands The Rivals and Box Social, as well as the Overland Park-based ska ensemble, Raging Hormones.

The top prize — 10 hours of free recording time at Alibi 6 Recording studios, 920 Del. — has band members appropriately amped.

“Any prize is great, but recording time is really hard to get,” says Kevin Lawrence, Box Social frontman and guitarist.

Box Social will headline tonight’s event, Lawrence says. The quartet, which has 20 original songs in its “piano-driven indie rock” playlist, opened a previous Battle of the Bands show.

Acts will be judged by volunteers from 90.7 KJHK, Alibi 6 Recording and Kief’s Audio-Video.

• Library Battle of the Bands6 to 9 p.m. Friday, July 30Swamp Hag (Lawrence)Box Social (Lawrence)The Rivals (Lawrence)Raging Hormones (Overland Park)
• more info

“We have very specific scoring cards for them to use,” Patton says. “We try to keep everything very professional. We even have the bands sign contracts for the event.”

Lawrence says Box Social (named for an obscure reference on the TV show “The Family Guy”) likes the professional treatment.

“We take our music seriously because we want it to sound great,” he says. “That’s what professionals do.”

Kenny Nall, guitarist for the five-piece group The Rivals, says he is looking forward to jamming garage-rock style at the contest.

“We play some covers, including The Strokes’ ’12:51,'” Nall says. “We’re a ‘the’ band, for sure.”

Members of Swamp Hag, from left, Franklin Fantini, PJ Tobar-Ballagh and Josh Gaston rehearse for the Lawrence Public Library's Battle of the Bands.

The Rivals, all ages 16 and 17, also performed at the Lawrence High School Battle of the Bands in April.

Patton maintains the competition is about entertaining kids while promoting a cool image for the library.

“We wanted to show young people that the library isn’t behind the times,” says Patton, who plans to display rock star autobiographies and other musical tomes at the free event.

Raging Hormones drummer Christopher Brower puts it another way: “The library, man, that’s where it’s at.”