The common alerting protocol (CAP) is a simple but general format for exchanging all-hazard emergency alerts and public warnings over all kinds of networks. CAP allows a consistent warning message to be disseminated simultaneously over many different warning systems, thus increasing warning effectiveness while simplifying the warning task. CAP also facilitates the detection of emerging patterns in local warnings of various kinds, such as might indicate an undetected hazard or hostile act. CAP also provides a template for effective warning messages based on best practices identified in academic research and real-world experience.

ITU-T Recommendation X.1303 also provides both an XSD specification and an equivalent ASN.1 specification (that permits a compact binary encoding) and allows the use of ASN.1 as well as XSD tools for the generation and processing of CAP messages. This Recommendation enables existing systems, such as H.323 systems, to more readily encode, transport and decode CAP messages.