For most campers, the number of stars a campsite gets reflects a level of quality and facilities. They're right but it's not as simple as that, especially since the rating system that appeared in 2012 or the new norms from April 2019 which apply to all rated (or re-rated) campsites since July 2019.
Pitches and rentals
Pitch surface area is one of the key factors for awarding stars. The average camping pitch is 80m² for a 1* or 2* (at least 70m²) and 89-114m² for 3*, 4* and 5* campsites (at least 80m²). A regulation also enforces a land occupancy rating. Basically, a rental shouldn't cover more than 30% of the pitch surface area.
Electricity connections for example are only compulsory near pitches at campsites rated 3* or more and the minimum amperage will depend on the land's rating.
Note that all the campsite pitches must be clean and tidy, the outside of the rental, its fixtures and fittings must be clean and in good condition; this applies to all campsite categories and is a priority among "new" rating norms in 2019. Upon application for a rating, an inspection is conducted to check this point.
Facilities and services
Other existing criteria. For example, a 2* must have washing facilities with individual cabins.
For a 3 star, a children's play area is required with more extensive services: internet access in communal areas, drinks for sale etc.
For 4* campsites and above, the campsite must have secure vehicle access at the entrance and there must be an eatery and bar on-site as well as somewhere to pick up supplies at the campsite. It should also have at least 4 pieces of equipment in the fitness area.
Last but not least, the top of the 5* pyramid requires a compulsory bathing area (lake or pool), deckchairs nearby and heated washing facilities. Plus there are optional services such as a spa area with massage, gym coach etc.
Reception and booking
Compared to a 1*, a 2* must have a reception that's staffed during the day. A 3* must be staffed 24 hours a day in two languages including English. 4* campsites must have reception staff with two foreign languages, a website and information tools in two foreign languages including English etc. Basically, 5* campsites stand out for features like three foreign languages at reception including English or being able to book online 24/7.
How about Wi-Fi?
In theory, Wi-Fi access is required at all pitches for campsites rated 2* or more since July 2019 so you should at least be able to read your emails at a low bandwidth. But there are exceptions e.g. if the campsite works with a deliberately "no Wi-Fi" establishment (ideal for zero-wave holidays or to really switch off from digital) or where there are real technical impossibilities. So check with the campsite beforehand.