I never remember Foxy's claws ever getting too long, but I would say that if they are scratching you quite regularly when you handle him or if perhaps Whisk walks a little differently because of them, then they're too long. I cut Tia's claws about every 2-3 months with nail scissors. You do have to be very careful when you do it though not to catch the quick and their toes, it's probably best to get someone else to hold them whilst you do it.