For any 4d N=2 superconformal field theories, there is a subsector described by a chiral algebra (or vertex operator algebra). It encodes useful information about the protected sector and also gives a handle to a strongly-coupled theory. One of the consequences is that the Schur index is identical to the vacuum character of the corresponding chiral algebra. I am going to argue that other observables, such as the Macdonald index and the Lens space index can also be obtained from the chiral algebra. I will be focusing on a simple set of examples, namely the Argyres-Douglas theories to illustrate this.