Normally when you are looking at declaring war you get a tip telling how severe your Warmonger penalty will be for this declaration.
However, when an ally asks you to declare a Joint War, you get no such information (or at least I failed to spot it).
The last time I did this I immediately received a denouncement for being a warmonger, so I assume there is a reasonably high warmonger penalty for it?
Does anyone know how big this penalty is? Is it based on the Casus Belli of the ally asking you to join? Is it just the standard Formal War penalty?