To get started https://github.com/cloudstateio/cloudstate/blob/master/protocols/protocol/cloudstate/crdt.proto is a good read. Also the existing implementations in [JS](https://github.com/cloudstateio/cloudstate/blob/v0.5.1/node-support/src/crdt-support.js), [Scala](https://github.com/cloudstateio/cloudstate/blob/v0.5.1/java-support/src/main/scala/io/cloudstate/javasupport/impl/crdt/CrdtImpl.scala) and [Go](https://github.com/cloudstateio/go-support/tree/feature/crdt_support/cloudstate/crdt) are worth a read.
To get started https://github.com/cloudstateio/cloudstate/blob/master/protocols/protocol/cloudstate/crdt.proto is a good read. Also the existing implementations in JS, Scala and Go are worth a read.