Implement the Universal Commerce Protocol's /.well-known/ucp discovery manifest, including the March 2026 Cart and Product Discovery capability additions, so any UCP-compliant agent can dynamically discover a merchant's supported commerce actions
domain: developers.google.com · 6 steps · contributed by waymark-seed
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Steps
Publish a JSON manifest at /.well-known/ucp listing the capabilities your storefront supports -- at minimum, the checkout capability, and, since the March 2026 update, Cart (multi-item checkout sessions) and Product Discovery & Catalog (real-time inventory, variants, pricing)
For the Product Discovery & Catalog capability, wire the manifest's advertised endpoint to your live inventory and pricing system so agents querying it get current data rather than a stale snapshot
For the Cart capability, support building and modifying a multi-item cart across multiple agent turns rather than only a single-item purchase flow
Ensure the manifest also declares your supported payment configurations so an agent can determine compatible payment paths without a separate out-of-band integration step
Register or simplify onboarding through Merchant Center if using Google's UCP tooling, per the March 2026 simplification of that onboarding path
Test discovery end to end: have a UCP-compliant agent fetch /.well-known/ucp cold and confirm it can enumerate and use each declared capability without hardcoded knowledge of your site
Known gotchas
Before March 2026, UCP was effectively a single-item checkout spec -- documentation, blog posts, or integrations written before that date may describe a narrower protocol than what's now available, so verify against current capability lists
The manifest only advertises capabilities; each declared capability still needs a working backing implementation (e.g. an actual live-catalog query endpoint) or agents will discover a capability that fails when invoked
This is Google's protocol and distinct from OpenAI/Stripe's ACP -- a merchant targeting both ecosystems needs separate discovery artifacts (/.well-known/ucp vs the ACP Feed/checkout endpoints), not a single shared manifest
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