Agent protocol map
MCP, A2A and the commerce protocols as layers, with a note on what is still changing.
DeveloperProduct
Layers
| Layer | Question | Examples |
|---|---|---|
| Tools and data | How does a model reach a tool or data source? | MCP |
| Agent to agent | How do independent agents delegate and collaborate? | A2A |
| Commerce | How does an agent discover products and check out? | UCP, ACP (as reported) |
| Payment authorization | How is an agent allowed to pay, and how is it proved? | AP2 (as reported) |
How they stack
- Start with MCP for tools
- Add A2A only when agents must work with other agents
- Add a commerce protocol only if you sell through agents
- They complement each other; most real stacks combine two or three
Status note
- Last verified November 3, 2026, against secondary summaries
- Sources disagree on the status of some commerce protocols, so read each specification before relying on it
- Re-check before every architecture decision