Introduction

XCM is a language for communicating intentions between consensus systems. Concretely, XCM is a message format, it specifies how to craft messages that communicate intentions to other consensus systems. Some examples of consensus systems are blockchains and smart contracts. XCM comes from the Polkadot ecosystem, but is designed to be general enough to provide a common format for cross-consensus communication that can be used anywhere.

Its goal is to let blockchain ecosystems thrive via specialization instead of generalization. If there's no interoperability, a chain is forced to host all services and support all functionalities on its own. With XCM, we are able to achieve an ecosystem-wide division of labour: a chain can specialize and focus on its own business logic, and leverage the benefits of depending on other specialized blockchain for services that it does not provide.

XCM makes the following assumptions regarding the underlying environment:

1. Asynchronous: XCMs in no way assume that the sender will be blocking on its completion.
2. Absolute: XCMs are assumed to be delivered and interpreted accurately, in order and in a timely fashion. Once a message is sent, one can assume that it will be processed as intended. This guarantee has to be provided by the transport layer.
3. Asymmetric: XCMs, by default, do not have results that let the sender know that the message was executed correctly. If results are needed, a new message must be sent.
4. Agnostic: XCM makes no assumptions about the nature of the consensus systems between which the messages are being passed. XCM should be usable in any system that derives finality through consensus.

XCM is constantly evolving; the format is expected to change over time. It has an RFC process to propose changes, which end up in newer versions, the current one being v3. To keep up with the development of the format, or to propose changes, go to the XCM format repository.