Yes, egg cartons may be composted!
They’re a good addition to a heap, especially one that is heavy with “greens“- the structure of the cardboard can help aerate a heavy heap and the cardboard can help soak up excess moisture.
They do need some moisture to break down though – if your heap is dry, splash some water on them and/or tear them up if you want them to break down quicker. Our labels are printed with soy ink and are made of paper so they are safe for your pile.