If stamp duty is payable, is it normally shared?
Frequency/market practice: There is no stamp duty. However, Luxembourg courts may require prior registration of a purchase agreement with the tax administration (Administration de l'Enregistrement, des Domaines, et de la TVA) in Luxembourg, in which case a fixed registration fee of EUR 12 is payable.
Is a separate tax covenant/indemnity or tax deed common?
Frequency/market practice: Very common (usually as part of the share purchase agreement and less common as a standalone document); usually covers all customary tax and VAT related aspects relevant for the target. General tax indemnities are also quite frequent in Luxembourg.