Stienhardt store on MCP

A small New York lab-grown diamond jeweler's live inventory, cart, and checkout, reachable by any Model Context Protocol client. The endpoint is Shopify's own per-store Universal Commerce Protocol (UCP) server; this repository registers it in the official MCP Registry and documents what an agent can and cannot do with it. Disclosure up front: we sell rings. Nothing here appraises or verifies a stone; the tools point you to the grading lab's own verification page.

Registry entry: io.github.JacobiusMakes/stienhardt-store (published 2026-09-01)
Endpoint: https://stienhard-stones.myshopify.com/api/ucp/mcp (streamable HTTP, 13 tools)
Discovery: https://stienhardt.com/.well-known/ucp (UCP 2026-08-25; Shop Pay, Google Pay, card)
Hosted helper: https://diamond-mcp.stienhardt.workers.dev/mcp (education tools plus live inventory search, with the agent profile UCP requires injected for you)

Try it (no signup, nothing to install)

Claude.ai (any plan): Customize, Connectors, Add custom connector, name Stienhardt, URL https://diamond-mcp.stienhardt.workers.dev/mcp, auth None. Then ask: "Find a 2 carat Dutch Marquise in stock and show me how big it reads in millimeters."

Claude Code:

Terminal

claude mcp add --transport http stienhardt https://diamond-mcp.stienhardt.workers.dev/mcp

MCP Inspector against the raw Shopify endpoint:

Terminal

npx @modelcontextprotocol/inspector --transport streamable-http --server-url https://stienhard-stones.myshopify.com/api/ucp/mcp

Note for scripts: Cloudflare returns error 1010 to Python's default Python-urllib user agent on the hosted helper; set any other User-Agent header. curl, Node, and MCP clients are unaffected.

initialize and tools/list answer anonymously. Every tools/call must carry arguments.meta.ucp-agent.profile, a URL to a UCP platform profile; see the gating table below.

What a self-registered agent can and cannot do (probed 2026-09-02)

Step	Result
`search_catalog` "Dutch Marquise 2 carat"	Ten live products with report-certified titles, prices, and links
`create_cart` with one variant	A cart with totals and a `continue_url`
`create_checkout`	A checkout object: status `incomplete`, totals, refund, shipping, privacy and terms links, `payment.instruments: []`, and a `continue_url` to Stienhardt's hosted Shopify checkout
`complete_checkout`	Not self-serve. Shopify grants direct completion case by case; the buyer finishes at the `continue_url` (Shop Pay, Google Pay, or card)

So the honest sentence is: an assistant can search live inventory, read the report numbers, build a cart, open a checkout, and hand you the link to pay. It does not pay for you.

The one thing an agent must know (capability gating)

Shopify fetches the profile URL you pass, requires Content-Type: application/json (GitHub raw fails with profile_malformed; a CDN such as jsDelivr works), requires a payment_handlers block, and exposes only the tools whose capabilities the profile declares. Declare too little and the tools "do not exist".

Tool family	Capability key the profile must declare
search_catalog	dev.ucp.shopping.catalog.search
lookup_catalog, get_product	dev.ucp.shopping.catalog.lookup
cart tools	dev.ucp.shopping.cart
checkout tools	dev.ucp.shopping.checkout (plus fulfillment, discount)

A working profile lives at https://cdn.jsdelivr.net/gh/JacobiusMakes/diamond-mcp@<sha>/agent-profile.json (source in the diamond-mcp repo). Pin the commit sha; jsDelivr caches @main for days. Shopify's fetcher also refuses *.workers.dev hosts, which is why the hosted helper points at the CDN copy.

Generic MCP clients do not send this profile on their own. The hosted helper injects it and exposes two clean tools, search_inventory and get_product, beside the eight open education tools.

The open education stack

diamond-mcp on npm (MIT): eight tools over a sourced, dated facts file and a 90-entry gemology encyclopedia. https://github.com/JacobiusMakes/diamond-mcp
Hugging Face dataset JacobiusMakes/diamond-gemology-encyclopedia (MIT).
"Dutch Marquise: Open Geometry Specification", DOI 10.5281/zenodo.21938900. A Dutch Marquise is an elongated hexagonal cut diamond, cut for brilliance; IGI reports read it as "Hexagonal Modified Brilliant".

Consumer-safety notes (they apply when an agent shops for jewelry)

Every agent-facing title carries the lab-grown qualifier (16 CFR 23.12).
The buyer confirms in a trusted checkout before any payment (UCP checkout spec); agents never hold card data.
Each stone's lab and report number are in the product data; verify them on the lab's own report lookup before you pay.
Returns and resizing are exposed in the checkout's policy links, because an agent buyer cannot try on.

Files

server.json: the registry manifest (GitHub namespace, remote streamable-http). Publish with mcp-publisher login github then mcp-publisher publish from this folder.
LICENSE: MIT.

Stienhardt sources certified Lab Grown Diamonds and hand-sets and finishes rings in New York City, by appointment. Store: https://stienhardt.com/?utm_source=github&utm_medium=readme&utm_campaign=mcp-store Questions: jgalperin@stienhardt.com.