Bicycle crank is wobbly My bicycle's crank is sorta wobbly - it tilts left or right, according to pressure applied to pedals. 

How do I fix it? What tools do I need?

Video showing the wobble.
The "bottom bracket" assembly is loose.  It may just be that it's a one-piece "cartridge" and is rattling around in the frame, or it may be that the unit is "loose bearings" and the bearing caps need to be adjusted.  Or there may have been some sort of failure of the bearings.

Regardless, the whole mess will need to be disassembled to a degree, and that requires some special tools (mainly a "crank puller").  So it may be best to take it to a bike shop.

Ran into virtually the identical situation today, working on a donated bike.  To do the job properly you need a crank puller, a "spanner" for the lockring, and a Park HCW-11 wrench for the "slotted" bottom bracket cup.  There are ways to do it without those special tools, but you risk mucking up the threads, etc.  And you probably need a new set of bearings (they're likely in "cages").