ARC · OPEN DATA
Protocol Matrix
Which agentic commerce protocols stores declare, and which actually work. One table, every protocol, the same four stages.
Live: n = 3,309 stores with a completed HTTP check, latest as of 11 Oct 2026 (UTC). Free and neutral: ARC takes no payment from any protocol, platform or model company.
Live figures (n = 3,309) update hourly from saved checks. Downloads are the dated weekly snapshot 2026-10-09.r3, n = 3,308, so their counts can differ.
JSON → · CSV (snapshot 2026-10-09) → · Open dataset → · Agent leaderboard → · Adoption tracker → · Add stores to the sample →
| Protocol | DeclaredA discovery document or marker is present. | ValidThe document parses or conforms. | UsableA tool or catalog answered. | TransactsA cart or checkout link came back, or the Index browser cart succeeded. |
|---|---|---|---|---|
| UCPUniversal Commerce Protocol (UCP) | 1611 / 330948.7% Measured | 1598 / 330948.3% Measured | 1487 / 330944.9% Measured | 1311 / 330939.6% Measured |
| ACPAgentic Commerce Protocol (ACP) | — Not measured | — Not measured | — Not measured | — Not measured |
| PAPPersonal Agent Protocol (PAP)Watching. The v0.1 specification is not yet published. | — Not measured | — Not measured | — Not measured | — Not measured |
| WebMCPWebMCP (Shopify storefront adapter) | 1451 / 329844% Measured | — Not measured | — Not measured | 39 / 5176.5% Inferred |
| MCPStorefront MCP and MCP well-known discoveryUsable counts stores whose /api/mcp server answers. Shopify moved cart and catalog tools to UCP, so those cart results count in the UCP row, not here. | 1519 / 330945.9% Measured | 1519 / 330945.9% Measured | 1519 / 330945.9% Measured | — Not measured |
| Agent paymentsVisa Trusted Agent Protocol and Mastercard Agent Pay | — Not measured | — Not measured | — Not measured | — Not measured |
Measured: ARC observed it directly. Inferred: two observations linked, not proof. Not measured: ARC has no saved evidence. That is not the same as zero adoption.
Protocols
- Universal Commerce Protocol (UCP)
Open standard launched by Google with commerce partners including Shopify. Published openly at ucp.dev.
- Agentic Commerce Protocol (ACP)
Open source (Apache 2.0), maintained by OpenAI and Stripe.
- Personal Agent Protocol (PAP)
Announced 6 Oct 2026 by Meta and Sierra with Genesys, Instinct, Rocket, Shopify, Stripe and Walmart. Described as an open standard.
- WebMCP (Shopify storefront adapter)
WebMCP is a proposed web standard in the W3C Web Machine Learning Community Group. Shopify ships tools for it on Liquid and Hydrogen storefronts.
- Storefront MCP and MCP well-known discovery
Model Context Protocol: created at Anthropic, now an open project under the Linux Foundation. Storefront MCP is Shopify's per-store server at /api/mcp.
- Visa Trusted Agent Protocol and Mastercard Agent Pay
Visa Trusted Agent Protocol is published by Visa as open source. Mastercard Agent Pay is Mastercard's framework. Both build on Web Bot Auth (HTTP message signatures, RFC 9421).
Methodology
Counts use each store's latest completed HTTP check saved by ARC. Failed checks are left out of the denominator. Each host counts once.
Measured means ARC observed it directly. Inferred means ARC links two observations that do not prove each other. Not measured means ARC has no saved evidence, and the count is not zero adoption.
A checkout link means a cart was created for one real product. It is not a completed purchase. ARC never places orders.
The sample is ARC's curated store list plus stores people checked. It is not all of e-commerce. Treat percentages as rates in this sample.
Reads make no store requests and no model calls.
Full method: /methodology. Agents can read this through ARC's free MCP tool protocol_matrix at /api/ask.
Cite this
ARC Protocol Matrix, arcreport.ai/protocols, accessed 2026-10-11. Licensed CC-BY-4.0. Data: arcreport.ai/data.
Free to use, share and adapt under CC-BY-4.0 with attribution to ARC, arcreport.ai. Raw rows: /data. Citation file: CITATION.cff. Corrections: /contact.