Commonsense Media is a site that will be mystifying to anyone without kids: they take books, movies, games, whatever, and essentially give a factual rundown of what happens in the work with an imaginary parent in mind.
I'll bet your mileage will vary on this site if you have a favorite, violence-strewn YA book, but I like that the site doesn't judge so much as record. They just put up a report on Alex Van Helsing that was actually a lot of fun for me to read:
Parents need to know that this action-packed vampire story has more violence and much less romance than the first book in the Twilight series. It also has more humor! The first two thirds of the story focus on the friendships between Alex and three new friends, the boarding school experience and Alex's discovery about his parents, his powers and the literary history of vampires. The final third veers into more traditional vampire storytelling, with blood drinking, holy water and death by staking. Despite several murders, the blood and gore level is not overdone.
It's strange to read your own work being analyzed this way, with little graphs and grades for curse words used (some) and whether or not any alcohol is consumed (no.) You can check it out here.