MCPG UCP Payment Plugin
EcosystemMCPG gateway plugin that gates purchasing tools behind merchant-discovered UCP checkout and releases calls after completed payment.
This is a developer tool for building UCP integrations. View on GitHub →
The MCPG UCP Payment Plugin is a Rust gateway plugin for putting selected MCP tools behind UCP checkout. It discovers a merchant through /.well-known/ucp, verifies the capabilities required by the tool, opens checkout at the merchant-advertised service endpoint, and returns the checkout state as an HTTP 402 challenge.
When the agent supplies a checkout session and payment instrument, the plugin asks the merchant to complete checkout. It releases the gated tool only after the merchant reports a completed status. The implementation includes same-origin endpoint enforcement, disabled redirects, checkout ownership binding, private-address response checks, metrics, and tracing.
Why This Matters for UCP
The plugin connects MCP tool execution to merchant-controlled UCP checkout, turning completed payment into the gate that authorizes a purchasing tool call.
UCP Capabilities
UCP Endpoint
Ecosystem — Endpoint not yet publicly available
Integration Example
plugins:
- id: dev.mcpg.payment.ucp
class: tool_gate
source:
path: ./plugins/libmcpg_plugin_payment_ucp.so
granted_capabilities: [network_outbound]
config:
tools:
store.checkout:
merchant_url: https://merchant.example
capabilities: ["dev.ucp.shopping.checkout"]Category
Developer ToolsUCP Status
EcosystemTags
Pricing
free
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Reviews
★★★★★4.6 (5 reviews)These are illustrative examples to show what reviews will look like. Submit your own experience below.
Y. Okonkwo
API Engineer · Feb 25, 2026
Good tool for UCP conformance testing. Runs fast and the output is easy to parse in CI. Would like a JSON output mode — currently only text.
B. Thompson
Staff Engineer · Mar 5, 2026
This saved us days of work. Dropped it into our pipeline and had UCP endpoint validation running in about 20 minutes. Documentation is accurate.
K. Park
Backend Developer · Feb 18, 2026
The best developer tool in this category. TypeScript types are correct and complete. Error messages actually tell you what went wrong.
E. Garcia
Senior Engineer · Jan 30, 2026
Solid tool. The test suite coverage is excellent. I found one edge case in the payment token validation that the maintainers fixed within 48 hours.
M. Fischer
DevTools Engineer · Mar 8, 2026
Integrated in an afternoon. The discovery endpoint just worked. The CLI flags are well-designed — composable, no magic defaults.
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