A quick question regarding the rogue's arcane trickster archetype. In his spell table (PHB p.98), there is no column with the proficiency bonus, like for the other spellcaster classes.
Does this mean that the arcane trickster doesn't add his proficiency bonus to his spell attack rolls ?
Because PHB p.205 says
Attack rolls
[…] Your attack bonus with a spell attack equals your spellcasting ability modifier + your proficiency bonus.
So I guess the column is just missing in the table p.98 ?
Best Answer
The rule says you add your proficiency bonus to spell attack rolls, so you do.
It's not missing from the table, it's just in another table on page 95, along with all the other core Rogue numbers. Spellcasters usually have spells as a core feature and they have all their level-based numbers in one table (see the Sorcerer just a few pages further on, on page 100). The Arcane Trickster though is a set of added abilities on top of Rogue. Rogues don't normally get spells, so the stuff that's normally in one table for a spellcaster — including proficiency bonus and spells known/slots — is for an Arcane Trickster split across the Rogue table and the Arcane Trickster table.
Looking at it another way: it wouldn't make sense to repeat Proficiency Bonus in both tables (it would be a waste of expensive page space), and it wouldn't make sense to combine the tables (all the spell stuff would be confusing for non–Arcane Trickster Rogue players), so it makes the most sense to have these things separate. Proficiency Bonus is the same for every Rogue of a given level,1 so it goes in the main Rogue table; spell details are not the same for every Rogue, so they go in a separate table. Being in separate tables doesn't imply that Proficiency doesn't apply to the spells.