D&Dtools1

With a word, you evoke a barrier of invisible force.
You project a field of invisible force, creating a short-lived protective barrier.
You gain a deflection bonus to your AC against a single attack; this bonus is equal to +1 per three caster levels (maximum +5).
You can cast this spell even when it's not your turn; however, you must cast it before your opponent makes his attack roll to gain the benefit.