learn / Merchant field guide

The protocol stack, without the alphabet soup

Locate a protocol’s job before asking whether you need it.

Merchant answer / Evidence review pending

ACP and UCP address commerce interactions. Their exact scope, versions and integration routes differ. Compare the operations your merchant needs and the surface you intend to serve. An open specification and a provider’s onboarding program are related but separate pieces of evidence.

What this establishes
A practical way to inspect evidence and make the next merchant decision.

What it cannot establish
An unresolved dependency remains. Treat affected claims as provisional. Live merchant deployment, private account eligibility, purchase completion or guaranteed AI selection.

Evidence dates and document versions remain attached to the ledger below. Editorial presentation reviewed 30 September 2026; this is not a new source verification.

Commerce semantics

Payments, trust and communication

AP2 focuses on payment authorization evidence. MPP and x402 address machine payment interactions. MCP connects applications with tools and resources; A2A coordinates agents. EMVCo’s agentic-payment work is currently a draft framework. These categories should not be collapsed into a single list of interchangeable checkout products.

Start with the merchant requirement

If your problem is incorrect product attributes, a transport protocol alone will not fix it. If your problem is access to a particular surface, confirm its documented onboarding route. Use a comparison to explain overlap and complementarity, then record the smallest set of capabilities needed by your stack.

Your next step

protocols ↗protocol compare ↗

Evidence ledger

Go to the source.

Primary documentation records what is publicly stated. It does not independently prove outcomes or your account’s eligibility.

ACP specification repository
OpenAI / Stripe · official primary · Checked 2026-09-28
Claim scope: Specification version and scope
Latest stable shown as 2026-04-17; development branch is not a release.
Source ID: acp-spec · Published: Not stated
UCP overview, 2026-08-25
UCP · official primary · Checked 2026-09-28
Claim scope: Discovery profile and commerce capabilities
Version-pinned profile discovery; declared capabilities do not prove successful transactions.
Source ID: ucp-spec · Published: Not stated
Agentic Payment Protocol v0.2
AP2 project · official primary · Checked 2026-09-28
Claim scope: Authorization mandates and receipts
Payment authorization within a commerce protocol; catalog API details are out of scope.
Source ID: ap2-spec · Published: Not stated
MCP specification 2026-07-28
MCP project · official primary · Checked 2026-09-28
Claim scope: Tools, resources, prompts and transport
Source ID: mcp-spec · Published: Not stated
Agent2Agent specification
A2A project · official primary · Checked 2026-09-28
Claim scope: Agent coordination
Latest released version shown as 1.0.0. Agent card app version is a different field.
Source ID: a2a-spec · Published: Not stated
EMV Agentic Payments – Framework for Specifications v1.0 DRAFT
EMVCo · official primary · Checked 2026-09-28
Claim scope: Card-based agentic payment framework
Draft, not a deployed payment rail or merchant certification.
Source ID: emv-draft · Published: 2026-09-01

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