A2A vs. AG-UI vs. MCP: Three Layers of the Same Stack
~12 min read
MCP, A2A, and AG-UI aren't competing choices — they answer three different questions (agent↔tools, agent↔agent, agent↔UI) and a real production system typically uses all three together.
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Key points
- •MCP, A2A, and AG-UI aren't competing choices — each standardizes a different connection type in the agent stack
- •MCP: agent-to-tool (tools, data, workflows). A2A: agent-to-agent (multi-agent coordination). AG-UI: agent-to-user (real-time UI streaming)
- •Reach for each based on the specific connection your system needs, not as an either/or decision
- •AG-UI can handshake with both MCP and A2A — tool outputs and multi-agent results flow through to the same unified UI layer
- •A realistic production system typically uses all three simultaneously, each for its own layer