This is a tool to find weaknesses in a Pokémon team. The term comes from the original (but outdated) Sweepercalc.
While Sweepercalc was based on a damage calculator, this uses the OU Checks Compendium which is much more accurate. It's a javascript implementation of my windows program, CompGen.
Click on a Pokémon to add or remove it from the team. The threatlist on the right should update to reveal which offensive threats you are least prepared for.
The edit field on the left will filter the list below it; press enter to add / remove the topmost entry from the team. (This is probably the fastest way to use it.)
Hover the mouse pointer over a threat to reveal its full list of checks. Click on any of them to add it to the team.