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AI agents such as Claude, ChatGPT and Gemini read stores and shop on a person’s behalf. Every live Fluid storefront answers them on its own host, with no app to install and no theme change. A merchant gets these from the start, and so does every store an agent launches on Fluid. This page lists what a shopping agent can use on any Fluid store, and what isn’t available yet. To build your own front end instead, see Build a headless storefront, which doesn’t include these features.

What every Fluid storefront serves

Replace https://<store> with the storefront’s host, such as https://<subdomain>.fluid.app or the store’s custom domain. When the storefront is turned off, or the company’s account is paused for billing, these paths answer the store’s 404 page, like any other missing storefront URL.
A merchant can replace the generated llms.txt. Publish an llms_txt template in the active theme, and the store serves that text in full instead. Keep its links to the store’s agent APIs, or agents won’t find them.

Send shoppers to the HTML page

The .md and .json versions are for the agent to read. When the agent links a shopper to a product or page, it should use the HTML URL. Keep any member path in the URL, such as https://<store>/<username>/products/<slug>: that path is how FairShare credits the member who shared it.

Universal Commerce Protocol (UCP)

UCP is an open standard for agent catalog, cart and checkout. Each Fluid store publishes its profile at /.well-known/ucp. Read it first: it names the versions the store serves and the endpoint for each, at /api/ucp/{version}. The request and response shapes are UCP’s own, in the specification the profile links to. A UCP cart or checkout session is a real Fluid cart. There are two ways to finish the purchase:
  • Pay inside the agent with Google Pay. When one of the company’s card accounts in Fluid Payments takes Google Pay through its payment provider, the store’s profile lists the com.google.pay payment handler, and each checkout session returns the Google Pay configuration for its country. The agent completes the checkout session with the Google Pay token, and reads the order afterwards.
  • Hand off to hosted checkout. Every cart and checkout session has a continue_url that opens Fluid’s hosted checkout at checkout.fluid.app with that cart. The shopper finishes the purchase there, with agreements, enrollment, subscriptions and card entry included. Use it when the store offers no Google Pay handler, and whenever a checkout session asks for something only the hosted checkout can collect.
Search for products in a store with UCP:
Use the version the store’s profile lists. 2026-08-25 is the current version at the time of writing.

What isn’t available through UCP yet

  • Payment methods other than Google Pay. Inside the agent, a checkout session completes only with Google Pay, and only on stores whose payment provider takes it. For any other payment method, hand the shopper the continue_url.
  • Signed-in buyers. An agent can’t link a shopper’s Fluid account through UCP, so UCP carts don’t carry member pricing, saved addresses or saved payment methods.
Check the store’s /.well-known/ucp profile for what it serves today.

Build the whole purchase yourself

An agent that needs more than UCP covers can use Fluid’s own APIs:

For the merchant’s own agent

The pages above are for agents that shop. An agent that builds or runs the store works through the authenticated APIs instead: