The grid in France works at 230 V and 50 Hz; the recorded sockets are Types C and E. At 230 V the supply matches what UK and European appliances expect, so no converter is needed.
The same socket system is used in Monaco, Czechia, Belgium and Poland, so one adapter covers all of them. Watch out when moving on: Cyprus, the Isle of Man and Ireland use a completely different system. In Europe, 6 of 50 recorded destinations use exactly this combination.
Protective earth
Grounded and ungrounded sockets may occur
France has sockets with a protective earth (Type E) and without (Type C). A plug that fits mechanically does not guarantee earthing.