# Protocol Compatibility Matrix

The first multi-protocol payment bridge for AI agent commerce

Trusteed supports 10 payment protocols: MCP, UCP, and SCP are in production; x402 and ACP are in sandbox; AP2 is experimental; Visa VIC, Mastercard MCAP, PayPal, and MPP are coming soon. MPP, from Stripe and Tempo Labs (IETF draft-httpauth-payment-00), extends x402 with native MCP/JSON-RPC transport. Plus AG-UI for real-time human-in-the-loop checkout and A2A for agent-to-agent communication. Merchants enable the protocols they need; agents pick the one they support. The Protocol Router handles detection, normalization, and settlement automatically.

## Protocol matrix

| Protocol | Origin | Version | Status | Inbound | Outbound | Settlement | Sandbox |
|---|---|---|---|---|---|---|---|
| ACP | OpenAI / Stripe | v1.0 | sandbox | yes | yes | Stripe | demo-store |
| AP2 | Google | v0.1 | beta | yes | yes | Cart Mandate | demo-store |
| x402 | Coinbase / Cloudflare | v1.0 | sandbox | yes | yes | USDC on-chain (Base Sepolia testnet) | available |
| VIC | Visa | v1.0 | sandbox | yes | yes | Visa tokenization | available |
| KYApay | Skyfire | v1.0 | coming-soon | yes | yes | Skyfire | coming-soon |
| PayPal | PayPal | v1.0 | sandbox | yes | yes | PayPal Commerce | available |
| MCAP | Mastercard | v1.0 | sandbox | yes | no | Stripe (pass-through) | available |
| UCP | Trusteed | 2026-04-08 | active | yes | yes | Protocol Bridge | demo-store |
| AG-UI | Trusteed | v1.0 | production-ready | yes | no | Real-time confirmation | demo-store |

## Protocol details

### ACP — Agent Commerce Protocol

Fiat payments via Stripe. The standard for OpenAI-compatible agents.

- Detection: X-Protocol header or Stripe signature
- MCP tools: create_cart, complete_checkout, preview_checkout
- View spec: https://github.com/agentic-commerce-protocol/agentic-commerce-protocol

### AP2 — Agent Payment Protocol v2

Google's cart mandate model for agent purchases. Designed for Google-ecosystem agents.

- Detection: AP2 mandate headers
- MCP tools: create_cart, complete_checkout
- View spec: https://ap2-protocol.org/specification/

### x402 — x402 Stablecoin Protocol

USDC stablecoin payments via HTTP 402 for crypto-native agents. Settles on the Base Sepolia testnet; no known real settlements.

- Detection: PAYMENT-SIGNATURE or X-PAYMENT header
- MCP tools: create_cart, complete_checkout
- View spec: https://www.x402.org/

### VIC — Visa Identity Credentials

Tokenized card payments using Visa Identity Credentials. 4-layer cryptography (JWE + X-Pay HMAC + MLE + HTTPS). 200+ tests. Awaiting Visa production credentials.

- Detection: VIC headers
- MCP tools: create_cart, complete_checkout
- View spec: https://developer.visa.com/

### KYApay — KYApay Identity-Linked Payments

Identity-linked JWT payments via Skyfire. Agent identity verification with payment execution.

- Detection: KYApay JWT headers
- MCP tools: create_cart, complete_checkout
- View spec: https://skyfire.dev/

### PayPal — PayPal Commerce Platform

PayPal Orders API v2 for agent-initiated purchases. Buyer approval via elicitation URL. Refunds require merchant approval. 400M+ PayPal accounts worldwide (PayPal Q4 2024 earnings report).

- Detection: X-Protocol: PAYPAL header or paypal_order_id in body
- MCP tools: create_cart, complete_checkout
- View spec: https://developer.paypal.com/

### MCAP — Mastercard Agent Pay

Mastercard Agentic Token payments via Stripe pass-through. Ed25519 HTTP Message Signatures (RFC 9421). Verifiable Intent receipts. 78 tests. Zero-code for merchants with Stripe.

- Detection: Signature-Input header with tag=agent-payer-auth
- MCP tools: process_agent_payment, check_agent_consent
- View spec: https://developer.mastercard.com/

### UCP — Universal Commerce Protocol

Universal discovery and checkout abstraction across all protocols. One endpoint, any payment method.

- Detection: UCP discovery at /.well-known/ucp
- MCP tools: search_products, get_product_details, get_merchant_profile
- View spec: /.well-known/ucp

### AG-UI — Agent-User Interaction Protocol

Real-time human-in-the-loop checkout via Server-Sent Events. Cryptographic token confirmation, state synchronization via RFC 6902 JSON Patch, and tool call verification.

- Detection: Content-Type: text/event-stream + SSE stream
- MCP tools: ag_ui_stream, ag_ui_confirm
- View spec: /specs/024-ag-ui-protocol/spec.md

## Why multi-protocol?

- **Agent choice** — Agents pick the protocol they support. No negotiation, no fallback errors.
- **Revenue maximization** — Do not lose sales because an agent only speaks x402 and your store only speaks ACP.
- **Future-proof** — New protocols are added via the Plugin Registry. Your integration stays the same.
- **Single integration** — One MCP endpoint, all protocols. The Protocol Router handles detection and routing.

## Frequently asked questions

**Q: How many protocols can a merchant enable?**

A: All supported protocols simultaneously. MCP, UCP, and SCP are in production; ACP and x402 are in sandbox (x402 settles on Base Sepolia testnet); AP2 is experimental; Visa VIC, Mastercard MCAP, and PayPal are coming soon. The Protocol Router selects the best match based on agent capabilities and merchant priority configuration.

**Q: Is there a cost per protocol?**

A: Protocol support is included in all tiers. Settlement fees depend on the protocol provider (Stripe for ACP, on-chain gas for x402, etc.).

**Q: Can I add a custom protocol?**

A: Yes. The Plugin Registry supports custom adapters. Contact us for Enterprise integration support.

**Q: How does protocol detection work?**

A: The Protocol Detector middleware inspects request headers, signatures, and body shape to identify the protocol with a confidence score (0.85-1.0). No manual configuration needed from the agent side.

---

Canonical HTML version: https://trusteed.xyz/en/protocol-coverage