The Quiet Standardisation of Agent Protocols - MCP, A2A, ACP Compared
TL;DR The 2026 agent ecosystem has, while nobody was paying close attention, converged on three protocols that solve different problems and partly overlap: MCP (Model Context Protocol), A2A (Agent-to-Agent), and ACP (Agent Communication Protocol). MCP is the model-to-tool protocol. It standardises how an agent talks to its tools, data sources, and local context. This is the one that has clearly won its layer. A2A is the agent-to-agent protocol. It standardises how separately deployed agents discover each other, exchange tasks, and pass results. Adoption is growing but the picture is less settled. ACP is the orchestration-and-runtime protocol. It standardises how an agent runtime exposes its lifecycle, state, and operations to the systems around it. Newer, more enterprise-focused, and not yet a clear winner. The mental model: MCP for tools, A2A for peers, ACP for the platform. Build with all three in mind even if you only need one today. Why Protocols, Why Now A year ago “agents” was still a debate about whether the things existed. By mid-2026 the debate has shifted. Agents exist. They do useful work. The interesting question is no longer “will this work” but “how do we connect them to everything else.” ...