UCP — Printing Press CLI

Prerequisites: Install the CLI

This skill drives the ucp-pp-cli binary. You must verify the CLI is installed before invoking any command from this skill. If it is missing, install it first:

1. Install via the Printing Press installer. It defaults binaries to $HOME/.local/bin on macOS/Linux and %LOCALAPPDATA%\Programs\PrintingPress\bin on Windows:

bash npx -y @mvanhorn/printing-press-library install ucp --cli-only

1. Verify: ucp-pp-cli --version
2. Ensure the reported install directory is on $PATH for the agent/runtime that will invoke this skill.

If the npx install fails (no Node, offline, etc.), fall back to a direct Go install (requires Go 1.26.6 or newer):

bash
go install github.com/mvanhorn/printing-press-library/library/commerce/ucp/cmd/ucp-pp-cli@latest

If --version reports "command not found" after install, the runtime cannot see the binary directory on $PATH. Do not proceed with skill commands until verification succeeds.

Real-Merchant Compatibility

v0.1 supports two interaction patterns:

| Command | Real merchants (e.g. checkout.coffeecircle.com) | Bundled mock (mock serve) | |---|---|---| | check <domain> | ✅ Any merchant publishing /.well-known/ucp | ✅ | | search / cart / checkout prep | ⚠️ Requires REST transport — most public merchants are MCP-only (deferred to v0.2) | ✅ Full end-to-end flow |

Known real merchants: checkout.coffeecircle.com (Shopify-hosted, MCP-only). v0.2 adds MCP transport client to unlock real-merchant transactions.

When to Use This CLI

Use ucp-pp-cli when an agent needs to interact with UCP merchants directly: probe a manifest, build a multi-merchant cart, run a search across known UCP-supporting stores, or prep a checkout draft for an AP2 mandate. It is the natural local pair to an AP2 CLI for the search-and-buy half of an agentic shopping flow. Skip it when you only need ChatGPT-side checkout (use an ACP-flavored tool) or when you only need merchant-side validation (use awesomeucp/ucp-doctor).

Unique Capabilities

These capabilities aren't available in any other tool for this API.

Cross-merchant discovery

• check — Fetch /.well-known/ucp for any domain and return a graded report covering schema validity, advertised transports, and capability coverage — works against any merchant publishing a UCP manifest, including MCP-only Shopify-hosted stores.

_Lets an agent screen a domain for UCP viability without standing up an SDK or hand-rolling manifest parsing._

bash ucp-pp-cli check checkout.coffeecircle.com --json

Reachability mitigation

• mock serve — Spawn a UCP-compliant reference merchant locally (pure-Go, no external runtime) so ucp check, search, cart, and checkout prep flows work end-to-end without a third-party UCP merchant or extra language toolchains.

_Lets an agent verify its UCP integration without coordinating with a live merchant or waiting for Google AI Mode approval._

bash ucp-pp-cli mock serve --port 8080

Command Reference

checkout — Operations on checkout

• ucp-pp-cli checkout — POST /checkout

Finding the right command

When you know what you want to do but not which command does it, ask the CLI directly:

bash
ucp-pp-cli which "<capability in your own words>"

which resolves a natural-language capability query to the best matching command from this CLI's curated feature index. Exit code 0 means at least one match; exit code 2 means no confident match — fall back to --help or use a narrower query.

Recipes

Boot a UCP test environment from scratch

bash
ucp-pp-cli mock serve --port 8080

Start the bundled pure-Go reference merchant; then run check 127.0.0.1:8080 from another shell.

End-to-end search-to-checkout against the mock merchant

bash
ucp-pp-cli search "coffee" --merchant 127.0.0.1:8080 --json

Fan out a query, normalize results, and pipe the first product into cart add then checkout prep.

Validate a real public UCP merchant manifest

bash
ucp-pp-cli check checkout.coffeecircle.com --json

Probe a Shopify-hosted UCP merchant. Returns a graded report even though the merchant advertises MCP-only transport (REST-only commands won't transact against it in v0.1).

Auth Setup

UCP has no global API key. Each merchant declares its own auth shape; the CLI identifies itself via the UCP-Agent: profile="<url>" header and signs requests with a per-agent ECDSA-P256 key. Run ucp profile init once to generate your profile. For account-linked flows, ucp auth link <merchant> walks an OAuth 2.0 flow per merchant (v1: print-mode — agent pastes the redirect URL back).

Run ucp-pp-cli doctor to verify setup.

Agent Mode

Add --agent to any command. Expands to: --json --compact --no-input --no-color --yes.

• Pipeable — JSON on stdout, errors on stderr
• Filterable — --select keeps a subset of fields. Dotted paths descend into nested structures; arrays traverse element-wise. Critical for keeping context small on verbose APIs:

bash ucp-pp-cli checkout --agent --select id,name,status

• Previewable — --dry-run shows the request without sending
• Non-interactive — never prompts, every input is a flag
• Explicit retries — use --idempotent only when an already-existing create should count as success

Agent Feedback

When you (or the agent) notice something off about this CLI, record it:

ucp-pp-cli feedback "the --since flag is inclusive but docs say exclusive"
ucp-pp-cli feedback --stdin < notes.txt
ucp-pp-cli feedback list --json --limit 10

Entries are stored locally at ~/.ucp-pp-cli/feedback.jsonl. They are never POSTed unless UCP_FEEDBACK_ENDPOINT is set AND either --send is passed or UCP_FEEDBACK_AUTO_SEND=true. Default behavior is local-only.

Write what surprised you, not a bug report. Short, specific, one line: that is the part that compounds.

Output Delivery

Every command accepts --deliver <sink>. The output goes to the named sink in addition to (or instead of) stdout, so agents can route command results without hand-piping. Three sinks are supported:

| Sink | Effect | |------|--------| | stdout | Default; write to stdout only | | file:<path> | Atomically write output to <path> (tmp + rename) | | webhook:<url> | POST the output body to the URL (application/json or application/x-ndjson when --compact) |

Unknown schemes are refused with a structured error naming the supported set. Webhook failures return non-zero and log the URL + HTTP status on stderr.

Named Profiles

A profile is a saved set of flag values, reused across invocations. Use it when a scheduled agent calls the same command every run with the same configuration - HeyGen's "Beacon" pattern.

ucp-pp-cli profile save briefing --json
ucp-pp-cli --profile briefing checkout
ucp-pp-cli profile list --json
ucp-pp-cli profile show briefing
ucp-pp-cli profile delete briefing --yes

Explicit flags always win over profile values; profile values win over defaults. agent-context lists all available profiles under available_profiles so introspecting agents discover them at runtime.

Exit Codes

| Code | Meaning | |------|---------| | 0 | Success | | 2 | Usage error (wrong arguments) | | 3 | Resource not found | | 4 | Authentication required | | 5 | API error (upstream issue) | | 7 | Rate limited (wait and retry) | | 10 | Config error |

Argument Parsing

Parse $ARGUMENTS:

1. Empty, help, or --help → show ucp-pp-cli --help output
2. Starts with install → ends with mcp → MCP installation; otherwise → see Prerequisites above
3. Anything else → Direct Use (execute as CLI command with --agent)

MCP Server Installation

1. Install the MCP server:

bash go install github.com/mvanhorn/printing-press-library/library/commerce/ucp/cmd/ucp-pp-mcp@latest

1. Register with Claude Code:

bash claude mcp add ucp-pp-mcp -- ucp-pp-mcp

1. Verify: claude mcp list

Direct Use

1. Check if installed: which ucp-pp-cli

If not found, offer to install (see Prerequisites at the top of this skill).

1. Match the user query to the best command from the Unique Capabilities and Command Reference above.
2. Execute with the --agent flag:

bash ucp-pp-cli <command> [subcommand] [args] --agent

1. If ambiguous, drill into subcommand help: ucp-pp-cli <command> --help.