The Pain: You've heard of MCP, A2A, AG-UI individually — each makes sense alone. But in your head they're scattered: what's the actual relationship? How do they work together in a real system? Do I need to adopt all three?
What You'll Learn: How the three protocols coordinate within one agent system, and the complete panorama of 2026 production-grade agent infrastructure.
The Three Protocols in One Picture
┌────────────────────────────────────────────────────┐
│ User (Human) │
│ │ │
│ ┌───────▼────────┐ │
│ │ AG-UI Layer │ ← human: dashboards/ops/progress │
│ └───────┬────────┘ │
│ │ │
│ ┌───────▼────────┐ │
│ │ Supervisor │ ← manager: decompose/schedule │
│ │ Agent │ │
│ └───┬────────┬───┘ │
│ ┌────────▼──┐ ┌──▼─────────┐ │
│ │ Worker A │ │ Worker B │ ← A2A: agent collaboration │
│ └─────┬─────┘ └─────┬──────┘ │
│ │ │ │
│ ┌─────▼─────┐ ┌─────▼──────┐ │
│ │ tools/API │ │ knowledge │ ← MCP: agent ↔ tools │
│ └───────────┘ └────────────┘ │
└────────────────────────────────────────────────────┘
The three protocols are not three separate systems — they're three vertical layers of the same agent system:
| Layer | Protocol | Role |
|---|---|---|
| Top | AG-UI | agent's face to humans (display/interaction) |
| Middle | A2A | agent-to-agent collaboration (schedule/division) |
| Bottom | MCP | agent's hands to tools (capability/data) |
Core insight: the three protocols are "division of labor," not "options" — a production agent system needs all three layers.
Three layers, not three options: tools + team + face.
Why Three "Layers," Not Three "Choices"
Many think MCP/A2A/AG-UI are three options — "which should I use?"
That's a misconception. They solve three different dimensions, like a building needing foundation, structure, and facade — not pick-one-of-three, but all-three-together:
Without MCP: agent has a brain but no hands (can't reach tools)
Without A2A: agent has hands but works solo (can't collaborate)
Without AG-UI: agent can work but nobody understands it (can't commercialize)
Missing any layer, the agent system is incomplete.
My Practice: Full Landing of Three-Layer Protocol Thinking
My one-person company agent system hasn't adopted the three SDKs, but all three layers of "protocol thinking" are landed:
| Layer | Implementation | Article |
|---|---|---|
| MCP layer | unified tool interface (AgentTool protocol) | D1 |
| A2A layer | Supervisor + Worker division | D2 + D4 |
| AG-UI layer | progress board + structured output | D3 |
Complete flow example:
User (via AG-UI): analyze this month's logistics costs
① AG-UI layer: show "analysis started" progress
② Supervisor (A2A layer): decompose →
"query data → calc metrics → generate report → push"
③ MCP layer: call database tool for data
④ Worker B (A2A): calc metrics
⑤ Worker C (A2A): generate report
⑥ AG-UI layer: show structured report card + drill-down
Each layer does its own job, collaborating to complete one full business flow.
A Decision Table: When to Adopt Which Layer
| Your situation | Layer to adopt | Priority |
|---|---|---|
| Agent can't reach external tools | MCP layer | P0 |
| Multiple agents collaborate chaotically | A2A layer (Supervisor) | P0 |
| Agent faces users/customers | AG-UI layer | P1 |
| Agent is for your own use only | AG-UI can wait | - |
Suggested order: MCP first (can work) → A2A (collaborate) → AG-UI (commercialize).
The Complete Panorama of 2026 Agent Infrastructure
Zooming out, production-grade agent infrastructure in 2026 looks like:
Model layer: LLM (reasoning engine)
↓
Protocol layer: MCP (tools) + A2A (collaboration) + AG-UI (interaction)
↓
Engineering layer: Supervisor + scene isolation + tool whitelist + observability
↓
Governance layer: audit logs + correction sedimentation + evals
These four layers are the complete "cage for AI" framework — from model to governance, each layer has corresponding practice (our series C and E cover them).
Model → Protocol → Engineering → Governance: the full cage.
Where You Are Now
You've now completed the full cognitive journey through 2026's agent protocol trio:
- D1 MCP: the USB port (tool layer)
- D2 A2A: the phone (collaboration layer)
- D3 AG-UI: the face (interaction layer)
- D4 Supervisor: the manager (organization layer)
- D5 Panorama: how the three layers coordinate (this article)
Remember: protocols aren't "pick one," they're "build three layers." A commercial agent system = hands (MCP) + team (A2A/Supervisor) + face (AG-UI).
That's the complete answer for 2026 agent infrastructure.
About the author: Wu Ji (无记) — AI & digitalization practitioner focused on Agent engineering, Loop Engineering, and digital transformation. Practical, hands-on tutorials — follow along and it just works.
Top comments (0)