Villgger

My friend recently challenged me to try and get on his server that is modded without knowing the mods. I have the IP and port however it says when I hover over the X "Incompatible FML modded server Server has additional mods that may be needed on the client" And when connecting it says "Failed to synchronize registry data from server, closing connection" Are there any websites/tools or clients that will show me what mods I need to join my friends server?