Formality criteria for algebras over operads

We study some formality criteria for differential graded algebras over differential graded operads. This unifies and generalizes other known approaches like the ones contained in [9] and [14]. In particular, we construct general operadic Kaledin classes and show that they provide obstructions to formality. Moreover, we show that an algebra A is formal if and only if its operadic cohomology spectral sequence degenerates at E 2 .