A group-based communication platform may be utilized to execute one or more processing actions via respective external application systems based on messages exchanged among client devices via the group-based communication platform. A particular processing action may be executed for a particular message by generating a container including contextual data and payload data, wherein the payload data comprises the message for which the processing action is to be performed. The container is provided to the external application system via a proxy endpoint, thereby causing the external application system to execute the processing action based on the data included within the container.