  Quantum contextuality is a key nonclassical feature essential for
understanding advantages in quantum computation and communication. We introduce
a new framework to study contextuality based solely on information processing
statistics. This simple and intuitive perspective leads to a powerful criterion
denoted as rank separation for identifying contextuality in various quantum
scenarios. We showcase the power of this technique through several
applications, including a new derivation of Hardy's quantum excess-baggage
theorem, and a simplified proof of contextuality for minimum error quantum
state discrimination. Finally, we show as a prominent example that quantum
contextuality provides the resource in optimal phase-covariant and universal
cloning schemes, hence establishing it as a fundamental source of
nonclassicality in all known optimal quantum cloning scenarios.
