# Build my own point of sale store on Crystallize, like POS Universe

I want a storefront for my business that works like **POS Universe** (https://pos-universe.superfast.shop), a demo store built on Crystallize: A complete till in the browser on the store’s own Crystallize catalogue: choose a grocery, fashion or tools store, sign in with a fingertip, scan with the camera, and the customer display sells the item just scanned — offline, on hardware the store already owns.

The content model and the wiring below are proven in that store: keep them for the features I want, and rename things to fit my trade. If a feature doesn't fit my business, leave its parts out rather than forcing it. Everything I see is mine to decide: brand, colours, typography, layout, copy and pages. Don't copy the demo's look; build my brand.

What the demo does: point of sale, click and collect, stock per location, campaigns, ai concierge. It is B2C, in English, Norwegian, Swedish, Dutch; my markets and languages may differ.

## How to work with me

- You need to run commands, edit files and use MCP tools. If you can't (for example in a plain chat), tell me, and suggest I paste this prompt into Claude Code, Cursor or another coding agent instead.
- Ask your questions a few at a time (three to five), in the order of the steps below, and suggest a sensible default for each so I can just say yes. Ask each thing once, even where two lists overlap, and ask the ones that change the build first. Don't start a step before the one before it is done.
- The technical detail below is for you. Talk to me in plain words, and explain a choice only when I need to make it.
- Keep the folder empty until step 5, apart from `.env.local`.
- Never ask me to paste an access token secret into the chat, and tell me not to paste a filled-in command or its output either. Tell me which command to run or which file to put it in, and I'll do it.
- Before you create or change anything in Crystallize, show me the plan (shapes, pieces, topics, price variants, markets) and wait for my yes. Before an import, show me a sample of five items.
- Use the Crystallize skills (the `skills` MCP tool, or the use-crystallize plugin) for how-to: `content-model`, `information-architecture`, `taxonomy`, `data-creation`, `mass-operations`, `pricing`, `query`, `mutation`, `js-api-client`, `responsive-images`, `payments`, and when this store needs them `subscriptions`, `bookable-resources`, `vector-ranking` and `permissions`. Where this prompt and a skill disagree, the skill wins. Check the live schemas with the MCP instead of guessing field names.
- When something I asked for isn't possible in Crystallize the way I pictured it, say so and offer the closest thing that is.
- **The storefront never reads from the Core API on customer-facing pages.** Products, public prices, stock and content come from the Discovery API and the Catalogue API; confidential prices (negotiated B2B price lists) from the Catalogue API on the server.
- **Use the Shop API for everything about customers:** carts, checkout, customers, orders (including orders created directly, such as renewals), order meta, pipeline stages, payments and subscription contracts. Take the customer identifier from the server session, never from the browser. The Core API is for setup scripts, back-office tools, scheduled jobs and what the Shop API can't do, always on the server and never once per page view.

## Step 1: Crystallize tenant, tokens and MCP

Ask me:
1. Do I have a Crystallize account and a tenant for this store? If not, I sign up for free at https://app.crystallize.com/signup and create an empty tenant. Ask for its **tenant identifier**.
2. Do I have access tokens? If not, tell me: in the Crystallize App, go to **Settings → Access Tokens → Generate a new token**, name it, and keep the ID and the secret (the secret is shown once). A token acts with its user's role, so while we build, that user needs to be Tenant Admin (or have a role that can write shapes, pieces, topics, items and prices and run mass operations). Once the store is built, switch the MCP to a token from a read-only user.
3. Is the Crystallize MCP connected, with write access? Check that you have its write tools (`run-mass-operation`, `mutate-core`), not only the read tools (`tenant-overview`, `fetch-content-model`): with only the read tools, it was added without `?exposeWrite=true`. If it's missing, have me run this in my terminal with my own token, then restart you:
   ```bash
   npx add-mcp "https://mcp.crystallize.com/mcp?exposeWrite=true" \
     --header "X-Crystallize-Access-Token-Id: <token id>" \
     --header "X-Crystallize-Access-Token-Secret: <token secret>"
   ```
   If the MCP can't be connected in my tool, say so and fall back to scripts that call the Crystallize APIs with the tokens from `.env.local`.
   In Claude Code, also suggest the Crystallize skills: `/plugin marketplace add crystallizeapi/ai`, then `/plugin install use-crystallize@crystallize-ai`. The plugin brings its own read-only Crystallize MCP entry with placeholder credentials: keep using the one added above (and add `&exposeSkills=false` to its URL once the plugin's skills are installed).
4. Confirm the connection with `tenant-overview`, and tell me what's already in the tenant. If it isn't empty, ask whether to build next to what's there or in a fresh tenant.

The storefront needs the tenant identifier and its own credentials: an access token pair for the Shop API (server only), and a static auth token if Discovery and the Catalogue API are secured. Don't reuse the admin build token in production. Put them in `.env.local` (have me fill in the secrets) and make sure `.env*` is in `.gitignore`.

## Step 2: my business and my brand

Ask me:
- What I sell, who buys it, and what makes us different. My brand name and a one-line pitch.
- My markets, currencies and languages, and my VAT/tax setup.
- Where my product data lives today: a spreadsheet or CSV, an export from Shopify, WooCommerce or another platform, a PIM or ERP, my current website, or nothing yet. Where my product images are.
- My brand: logo (SVG if I have it), colours, typefaces, tone of voice, and two or three sites whose look I like. If I have no brand guide, propose a direction from my answers and show it before building pages.
- Where it should run: my own domain, and hosting (suggest Vercel for Next.js).

Then ask what is particular to this kind of store:

- Which stores and tills: how many stores, registers per store, and which devices (iPad, Android tablet, phone, PC)? Is there a second screen facing the customer?
- What do I sell over the counter: weighed fresh produce (PLU codes, tare), deposit on drinks, age-limited items (beer hours), sizes and colours, items sold by the unit?
- Barcodes: do my products carry GTIN/EAN in Crystallize, and which in-store price or weight barcodes (prefixes 20–25) do my scales print?
- Payment: cash, a standalone card terminal, Tap to Pay on the phone (which provider: Stripe Terminal or Adyen, and is the agreement in place), mobile payment, gift cards?
- Receipts: printed (which printer: Epson or Star, USB, Bluetooth or network), digital by QR, or both? Which country's cash register rules apply (in Norway, kassasystemforskriften: electronic journal, X/Z reports, SAF-T Cash Register)?
- Staff: roles (cashier, manager, admin), which actions need a manager (discounts over a limit, returns, cash drops), and do staff share devices?
- Stock: one stock location per store, a central warehouse, transfers between stores? Click and collect and ship-from-store?
- Promotions: multi-buy, percentage off, member prices, coupon codes; are they already set up for the web shop?
- Does the till have to keep selling when the internet drops (it should)?

## Step 3: the content model

Create this in my tenant with the MCP, renamed to fit my trade, after I have approved the plan. Keep the structure: it is what the storefront's features depend on.

Build in dependency order, since mass operations run in sequence with no rollback: pieces and shapes (empty first, then their components), topic maps (at most 30 topics per `topic/create`), price variants, markets and VAT types, the folder tree (two to four levels, five to twelve per level), and only then items. Use lowercase-hyphen identifiers. Decide now which fields are translated and which are discoverable. Restrict every item relation with `acceptedShapeIdentifiers`. Never add price or stock components to a shape: variants have them built in.

The till sells from the same catalogue as the web shop; nothing is copied into a second product database.

- Products and variants as the web shop has them. The till needs, per variant: SKU, price per price variant (one per currency; say whether prices include VAT), stock per stock location, images, and barcodes (a GTIN/EAN component or an identifiers chunk on the variant, discoverable).
- Grocery facts where they apply: sold by weight with price per kg and tare, deposit per unit, age limit, organic flag, PLU code, storage (ambient, chilled, frozen), allergens. Keep them as typed components so the till can read them.
- **POS screens as Crystallize grids:** one grid per till screen, laid out by the merchandiser with column and row spans; product cells become keys, folder cells drill in. Without grids, screens are generated from the catalogue folders under a root path, with subfolders as filter chips.
- Related products (an item relation) and topics, used for "goes well with" on the customer display.
- One stock location per store (and the central warehouse); order pipelines for click and collect (new, picking, ready, collected) and for ship-to-customer.
- Customers with customer groups (for member prices) and consent fields.
- Promotions in Crystallize (multi-buy, percentage, member, coupon codes), the same the web shop uses.

## Step 4: my data

Import my products and content with mass operations, mapping my data onto the model: validate each file with `build-mass-operation`, run it with `run-mass-operation` and follow it with `get-mass-operation-status`. Read the operation logs, not just the task status: a task can finish as complete with failed operations, and there is no rollback. Give every upsert a `resourceIdentifier` so a re-run updates instead of duplicating, and chunk large imports. Start with a small batch, check it in the Crystallize App with me, then run the rest.

Publish every imported item in each language: the storefront only sees published versions (in a mass operation, `item/publish` needs real `itemId`s). Import images from URLs with `copyRemoteAsset`, or upload them (presigned upload, then `registerImage`). Renditions are generated in a queue: after a large import, republish once they exist, and have the storefront fall back to the original image URL while `variants` is empty. Before building pages, query Discovery once; if the tenant isn't ignited yet, run `igniteDiscoApi` (with `stacks: opensearch` if we use vector ranking), wait for the task to complete, and allow a few minutes. If I have no data yet, create a small, clearly labelled placeholder set (ten or so products) so we can build the pages, and remind me to replace it.

- The demo sells from three existing Crystallize tenants, food-universe (grocery, with three POS grids), fashion-universe and tools-universe (screens from folders), in EUR. No product data was made for the till.
- From me: my catalogue in Crystallize with prices, stock per store and barcodes; the stores, registers and staff; my payment provider and printer; my promotions.

## Step 5: the storefront

- Next.js (App Router), a PWA with a service worker; every register setting is per device (tenant, catalogue language, price variant, VAT mode, stock location, root path, grid ids, store, register id).
- **Catalogue API** for grids and folder screens, and **Discovery** for search and barcode lookup (`sku` or GTIN `equals`). The till keeps the whole catalogue offline: a server route builds one bundle (products, screens, folders) with a content hash; the browser stores it in IndexedDB, re-checks the hash every 15 minutes, and caches the images in Cache Storage. Every scan and search hits the local copy first.
- **Orders through the Shop API:** a server route gets a Shop API token with the `order` scopes from an access token pair, then creates the order with its payments, the store's stock location, and meta (sale id, register, receipt number, cashier). Sales are written to the device's journal first and synced when online; retries look up the sale id first so a lost response never creates two orders. Returns are credit notes related to the original order.
- **Journal on the device:** an append-only IndexedDB journal with a hash chain, X and Z reports and SAF-T Cash Register export. Never let the server be the only copy of a sale.
- **Staff:** PINs hashed per device; passkeys (WebAuthn with the platform authenticator, user verification required) verified on the device with WebCrypto: challenge, origin, rpId hash, the UP and UV flags, the signature and the sign counter. Manager override offers only the passkeys of staff allowed to approve.
- **Hardware from the browser:** camera scanning with `BarcodeDetector`, and a WASM decoder (zxing) where it is missing; receipt printers and the cash drawer over WebUSB, Web Bluetooth or Web Serial with a small ESC/POS encoder.
- **Customer display:** a second window fed over a `BroadcastChannel` (or a local relay for a separate tablet): the lines, the item just scanned with its image and allergens, related products, and a QR for the digital receipt (a signed, short-lived token that carries the receipt itself, so no database is needed).
- **Tap to Pay:** Stripe Terminal (server-driven) or Adyen's cloud Terminal API behind server routes, with the sale reference as the idempotency key; a phone as the reader needs a native shell (Capacitor) and the Apple Tap to Pay entitlement.
- **Assistant (optional):** an LLM with tools over the catalogue search, product details and stock; every product it shows is validated against the tool results and filled from the catalogue. Without a key, a local keyword, price and allergen search.
- Env: `CRYSTALLIZE_TENANT_IDENTIFIER`, `CRYSTALLIZE_ACCESS_TOKEN_ID`, `CRYSTALLIZE_ACCESS_TOKEN_SECRET`, `NEXT_PUBLIC_POS_GRID_IDS`, plus `POS_RECEIPT_SECRET` for digital receipts and the payment provider's keys.

Build my design, not a demo's: my typefaces, colours and tone, with pages that suit my products. Show me the home page, a category and a product page early, and adjust the design with me before building the rest.

Every page is built for search engines, answer engines and AI agents from the start, not added at the end:
- **SEO:** server-rendered HTML, one `<h1>`, a unique title and description, canonical URLs, `hreflang` per language, a sitemap and `robots.txt`, and clean, translated paths.
- **Structured data:** JSON-LD on every page that has a subject: `Organization` and `WebSite` (with a `SearchAction`) on the home page, `Product` with `Offer` (price, currency, availability) on product pages, `BreadcrumbList` on categories and products, `Article` or `Recipe` on content. Generate it from the same data as the page.
- **GEO, for answer engines and agents:** `/llms.txt` (an H1, a summary, links to every section), `/llms-full.txt`, and a Markdown twin of every page (its URL plus `.md`, or `Accept: text/markdown`), with prices, stock and facts written out in plain sentences.
- **Agents can act, not only read:** register the store's actions (search, add to cart, check availability) with WebMCP (`navigator.modelContext.registerTool`, or annotated forms), and keep the accessibility tree clean: semantic HTML, labelled controls, real buttons and links.
- **Fast and stable:** responsive images from Crystallize, no layout shift (reserve space for images and late content), little client JavaScript. Aim for 100 in every Lighthouse category (Performance, Accessibility, Best Practices, SEO; heavy 3D or video pages may score lower on performance) and pass every Agentic Browsing check.

## Step 6: run it, then ship it

Run it locally and walk me through each feature above with my own data. Fix what I find. Before you call it done, run Lighthouse on the home page, a category and a product page (`npx lighthouse <url> --only-categories=performance,accessibility,best-practices,seo,agentic-browsing`), validate the JSON-LD (https://validator.schema.org), open `/llms.txt` and a page's `.md` twin, and fix what falls short. Deploy only when I ask: set the same environment variables on the host, point my domain, and give me the live URL.

## Watch out for

- The till's API routes create orders with the server's credentials: put authentication or a private network in front of them before real keys are used, and lock the credentials to the tenant.
- Prices: say whether a price variant includes VAT, and round cash to the currency's smallest coin where the law asks for it (Norway: whole kroner).
- The Catalogue API has no "list grids" query: configure the grid ids.
- Some tenants return an empty `variants` list with a `defaultVariant`: fall back to it.
- Discovery's schema is generated per tenant (GTIN fields only exist where the tenant has them): fall back to the offline index when a query fails validation.
- Passkeys need HTTPS and a stable origin; they are per device unless public keys are shared between registers.
- Cash register law: the journal, receipts and reports are regulated; a product declaration may be needed before real use.
- Don't invent facts about my business (prices, stock, certifications, delivery promises). Ask, or leave a clearly marked placeholder.

And for every Crystallize store, from the skills:
- **Orders:** create and change them through the Shop API `/order` (`createFromCart`, `create`, `setMeta` with `merge: true`, `addToStage`, `setPayments`). Editing an order in Core adds a duplicate to the Shop API's list. Read a customer's orders with the identifier from the session, `limit: 100`, grouped by `coreId` (keep the newest). Seed order history through `/order` `create`, not Core `registerOrder`. The order id is the cart id; don't call `fulfill` after `createFromCart`.
- **Payments:** create the order from the payment provider's verified webhook, never from the browser, once per cart.
- **Cart meta** goes in `hydrate(input: { meta })`; `hydrate` is the whole cart, so send every line each time.
- **Images:** serve them straight from Crystallize (not through an image optimizer such as `next/image` in its default setup): a WebP `srcset` from the returned `variants` with an accurate `sizes`, falling back to the original URL while renditions are missing. Replace an image by uploading a new one, not with `registerImageRevision`.
- **Ranking (if the store ranks per shopper):** check that `__type(name: "RankByInput")` exists; pass `context` as a variable, with `userTaste` entries of `{ vocabulary, weights, magnitude }` (magnitude = the square root of the sum of squared weights); `tieBreaker` is required; don't combine `sorting` with ranking, and page with `skip` and `limit` inside the rerank window; introspect `TenantRankByField` for field names; leave `context` out when there's no taste; use `explain: true` only for tuning.
- **Bookings (if the store books):** durations are in seconds; the role needs the `bookingPolicies` permission; put the customer on the cart before `bookSkuItem`; every `hydrate` must resend each booked line with its window and unit, or the booking is cancelled; remove a booking by re-hydrating without it.

## Done when

- My tenant has the content model above with my products, prices and images in it.
- The storefront runs on my domain in my brand, and every feature I chose works with my data: we have clicked through each one together.
- Lighthouse scores close to 100 in every category and every Agentic Browsing check passes on the home, category and product pages.
- I know how to add a product, change a price and publish, in the Crystallize App.