Beyond Message Passing: A Semantic View of Agent Communication Protocols

TL;DR

This paper introduces a layered semantic framework for agent communication protocols, analyzing 18 protocols to identify gaps in semantic support and proposing a research agenda for more robust, interoperable agent systems.

Contribution

It systematically categorizes agent communication into three layers, analyzes existing protocols, and highlights the need for better semantic mechanisms beyond message passing.

Findings

Most protocols excel in transport and lifecycle management but lack semantic verification mechanisms.

Semantic responsibilities are often embedded in prompts or application logic, increasing complexity.

Identifies technical debt and offers guidance for protocol selection in diverse settings.

Abstract

Agent communication protocols are becoming critical infrastructure for large language model (LLM) systems that must use tools, coordinate with other agents, and operate across heterogeneous environments. This work presents a human-inspired perspective on this emerging landscape by organizing agent communication into three layers: communication, syntactic, and semantic. Under this framework, we systematically analyze 18 representative protocols and compare how they support reliable transport, structured interaction, and meaning-level coordination. Our analysis shows a clear imbalance in current protocol design. Most protocols provide increasingly mature support for transport, streaming, schema definition, and lifecycle management, but offer limited protocol-level mechanisms for clarification, context alignment, and verification. As a result, semantic responsibilities are often pushed into prompts, wrappers, or application-specific orchestration logic, creating hidden interoperability and maintenance costs. To make this gap actionable, we further identify major forms of technical debt in today's protocol ecosystem and distill practical guidance for selecting protocols under different deployment settings. We conclude by outlining a research agenda for interoperable, secure, and semantically robust agent ecosystems that move beyond message passing toward shared understanding.