ucp-checkout-a2a
Implement UCP Checkout over the A2A (Agent-to-Agent) binding — enable autonomous agent-to-agent commerce using Agent Cards and structured message parts. Use when building agent-to-agent commerce flows.
Best use case
ucp-checkout-a2a is best used when you need a repeatable AI agent workflow instead of a one-off prompt.
Implement UCP Checkout over the A2A (Agent-to-Agent) binding — enable autonomous agent-to-agent commerce using Agent Cards and structured message parts. Use when building agent-to-agent commerce flows.
Teams using ucp-checkout-a2a should expect a more consistent output, faster repeated execution, less prompt rewriting.
When to use this skill
- You want a reusable workflow that can be run more than once with consistent structure.
When not to use this skill
- You only need a quick one-off answer and do not need a reusable workflow.
- You cannot install or maintain the underlying files, dependencies, or repository context.
Installation
Claude Code / Cursor / Codex
Manual Installation
- Download SKILL.md from GitHub
- Place it in
.claude/skills/ucp-checkout-a2a/SKILL.mdinside your project - Restart your AI agent — it will auto-discover the skill
How ucp-checkout-a2a Compares
| Feature / Agent | ucp-checkout-a2a | Standard Approach |
|---|---|---|
| Platform Support | Not specified | Limited / Varies |
| Context Awareness | High | Baseline |
| Installation Complexity | Unknown | N/A |
Frequently Asked Questions
What does this skill do?
Implement UCP Checkout over the A2A (Agent-to-Agent) binding — enable autonomous agent-to-agent commerce using Agent Cards and structured message parts. Use when building agent-to-agent commerce flows.
Where can I find the source code?
You can find the source code on GitHub using the link provided at the top of the page.
SKILL.md Source
# UCP Checkout — A2A Binding ## Before writing code **Fetch live spec**: Web-search `site:ucp.dev specification checkout-a2a` and fetch the page for the exact message structure, DataPart keys, and Agent Card format. Also review Google's A2A protocol spec for the underlying transport: https://google.github.io/A2A/ ## Conceptual Architecture ### What is A2A? A2A (Agent-to-Agent) is a protocol for autonomous inter-agent communication. UCP's A2A binding lets a Platform agent talk to a Business agent using structured messages rather than REST calls. ### How It Works 1. **Discovery**: Business publishes an Agent Card at the URL declared in their `/.well-known/ucp` profile under `services.dev.ucp.shopping.a2a.endpoint`. 2. **Communication**: Platform sends messages with checkout data in `DataPart` objects. Business agent responds with checkout state in `DataPart` objects. 3. **Identification**: Platform includes `UCP-Agent` header and `X-A2A-Extensions` header referencing the UCP spec version. ### Key Data Part Keys | Key | Direction | Purpose | |-----|-----------|---------| | `a2a.ucp.checkout` | Both | Checkout session data | | `a2a.ucp.checkout.payment_data` | Platform → Business | Payment credentials for completion | | `a2a.ucp.checkout.risk_signals` | Platform → Business | Optional risk signals | | `ap2.merchant_authorization` | Business → Platform | Merchant's JWS detached content signature for AP2 mandate flow | | `ap2.checkout_mandate` | Platform → Business | SD-JWT+kb credential proving user-authorized agent checkout | ### Message Structure Messages use A2A's standard format: - `messageId`: Unique ID (used for idempotency) - `contextId`: Session/conversation ID - `kind`: `"message"` - `role`: `"user"` (from platform) or `"agent"` (from business) - `parts`: Array of TextPart and DataPart objects Checkout data is carried in `DataPart` with the appropriate key. ### Idempotency The Business agent uses `messageId` to detect duplicate requests. Task tracking uses `taskId` with `contextId`. ### When to Use A2A - Fully autonomous agent-to-agent commerce (no human in the loop for most steps) - Multi-agent architectures where commerce is one capability among many - When you want the Business to maintain its own agent logic (not just expose tools) ### Implementation Guidance Before implementing, fetch the latest sample A2A Business Agent from https://github.com/Universal-Commerce-Protocol/samples (look for the `a2a/` directory) to see the reference pattern.
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