Everyone's favorite topic! As in mainland France, the menu includes the full price. The servers are paid full wages. Many French may leave a little extra. 5-10%

French waiters in the islands often ask for the full American style tip.

They've become accustomed to it and are not shy about asking for it. If they are "on the books" French employees, they already make a proper wage and are typically guaranteed insurance etc.

I leave 5-10% on both sides, and in St Barth