Cross-cutting
Stack
Where each protocol sits in the agent commerce stack, from discovery to reputation. A solid tinted block is the protocol's primary layer; dashed blocks are layers it also touches.
Layers come from each protocol page's frontmatter (primary layer and secondary layers), which the protocol writers set from the specification. Select a block to open the protocol page. Drag to pan; use the buttons to zoom.
- Primary layer (solid border, tinted)
- Secondary layer (dashed border)
- Border hue shows the family; the family name is also in each block's label and in the table.
- A dashed connector means the span skips a layer.
Interactive stack map
Stack as a table
| Layer | ERC-8004 | x402 | Visa TAP | OpenAI ACP | UCP | Stripe MPP | AP2 | Mastercard Agent Pay |
|---|---|---|---|---|---|---|---|---|
| Discovery | Secondary | Secondary | Not covered | Secondary | Secondary | Secondary | Not covered | Not covered |
| Identity and trust | Primary | Not covered | Primary | Not covered | Secondary | Not covered | Not covered | Secondary |
| Intent and authorization | Not covered | Not covered | Not covered | Not covered | Secondary | Not covered | Primary | Secondary |
| Checkout and orders | Not covered | Not covered | Secondary | Primary | Primary | Not covered | Secondary | Secondary |
| Payment credential | Not covered | Secondary | Secondary | Secondary | Secondary | Primary | Secondary | Primary |
| Settlement rails | Not covered | Primary | Not covered | Not covered | Not covered | Secondary | Not covered | Not covered |
| Post-purchase and disputes | Not covered | Secondary | Not covered | Secondary | Secondary | Not covered | Secondary | Not covered |
| Reputation and feedback | Secondary | Not covered | Not covered | Not covered | Not covered | Not covered | Not covered | Not covered |
| Family | Identity and trust | Payment execution and credentials | Identity and trust | Checkout and orders | Checkout and orders | Payment execution and credentials | Authorization and intent | Payment execution and credentials |
For how the layers combine in practice, see the compare matrix (“Layers covered” and “Composes with” rows) and the controls map.