- a "reasonable" time limit
- a specific geographic region (i.e: only in France, U.E, etc...) -> this is very often omitted, and "the whole world" is not valid.
- The non-competition has to be for a specific activity. This is often not understood and instead you find something like "not work for our competitor" or "not work for a company in this field". This is not specific enough and will be thrown out in court.
- There has to be a financial compensation.
Despite this, almost all the company that I worked for in France had non-applicable non-competes agreement in their contract. None of them offered a financial compensation and none had a specific region.
As far as I know, this is not a France-only thing, and non-competes creeps in almost any employment contract in the world, especially in the tech field. Learn your rights.
[0] https://www.service-public.fr/particuliers/vosdroits/F1910