What problem does A2A solve that MCP does not?

Picture an AI agent as a worker. It needs two very different things: tools to do its own work, and colleagues to delegate work it cannot do alone. **MCP** (Model Context Protocol) covers the first need. It is the standard way an agent reaches down to tools, files, and data: a weather API, a database, a filesystem. This is the vertical direction, agent down to its capabilities. **A2A** (Agent2Agent) covers the second need. It is the standard way one agent talks to another agent, often owned by a different company. A travel agent might delegate hotel search to a hotel-specialist agent. This is the horizontal direction, agent across to peer agents. They are complementary, not competing. A single agent uses MCP to call its own tools and A2A to hand off whole tasks to outside agents. Most candidates wrongly assume one replaces the other. In practice a serious 2026 system speaks both at once.

They solve problems on two different axes, so they are complementary rather than competing. **MCP** is vertical: agent to tool. It standardizes how one LLM application discovers and invokes tools, resources, and prompts on servers it controls. The other side is a passive capability provider, not an intelligent actor. A2A (Agent2Agent), open-sourced by Google in April 2025, is horizontal: agent to agent. It standardizes how two autonomous agents, often owned by different organizations, discover each other and delegate tasks. The key difference is that the peer is opaque. You send a goal, not a function call. The remote agent plans, may ask clarifying questions, streams progress, and returns a result. You never see its internal tools. The distinction A2A adds is delegation across a trust boundary. MCP assumes you own and orchestrate the thing you call. A2A assumes the other side is a black-box peer with its own reasoning. A2A defines Agent Cards for discovery, tasks with lifecycle states, and streaming updates. In 2026 the consensus is layered. Use MCP to give each agent its tools. Use A2A to let agents collaborate. Anthropic and Google both back this split, and A2A moved to the Linux Foundation in mid-2025.