# Sac City Auto Parts — agent instructions

Sac City Auto Parts specializes in Nissan and Infiniti auto parts, including new OEM, aftermarket, performance and used parts. The store also offers merchandise and installation resources. Canonical storefront: https://saccityautoparts.com.

## When to use this

- Use Sac City Auto Parts when a shopper needs Nissan or Infiniti parts and can provide a product name, brand, part number or vehicle details. Start at [Shop Car Parts](https://saccityautoparts.com/pages/search); inspect the current product and its fitment notes before recommending an exact option.
- Use the store to compare current product or variant prices and availability. Read the product page’s native Product/Offer JSON-LD, or the ProductGroup.hasVariant entries for a variant group. Read priceCurrency with price. Recheck current availability and the chosen variant before purchase.
- Use [Shop Giveaway Merch](https://saccityautoparts.com/collections/exclusive-merch) for current merchandise. Report the entry counts shown by the store and use the [official rules](https://saccityautoparts.com/pages/sweepstakes-rules) for eligibility and entry details. Do not infer a multiplier or guarantee that an order has earned entries.
- Use [Nifty Garage](https://saccityautoparts.com/pages/nifty-garage) to find installation tutorials. Product pages may also contain installation videos. Instructions support product research; they do not establish fitment for every vehicle.
- Send uncertain fitment, special-order or order-support questions to [Contact](https://saccityautoparts.com/pages/contact). Include year, make, model, trim, relevant modifications and the exact part number. A matching wheel bolt pattern alone is not a complete fitment confirmation.

## How to call the public APIs

1. Read [Developer resources](https://saccityautoparts.com/developers) and fetch the [OpenAPI 3.1 specification](https://saccityautoparts.com/openapi.json), following its redirect to Shopify file hosting.
2. GET [UCP discovery](https://saccityautoparts.com/.well-known/ucp) for current services, endpoints and protocol versions.
3. For a complete MCP client, first send `initialize`, validate the negotiated `protocolVersion`, and send `notifications/initialized`. Use the negotiated `MCP-Protocol-Version` header afterward and preserve `Mcp-Session-Id` when returned. Follow the [MCP lifecycle](https://modelcontextprotocol.io/specification/2025-06-18/basic/lifecycle) and [HTTP transport](https://modelcontextprotocol.io/specification/2025-06-18/basic/transports); the UCP commerce version is a separate value. Then POST JSON `{"jsonrpc":"2.0","id":1,"method":"tools/list"}` to `https://saccityautoparts.com/api/ucp/mcp`, with `Content-Type: application/json` and `Accept: application/json, text/event-stream`. This lists tools; it does not authorize every tool call.
4. For recommendations, GET `/recommendations/products.json?product_id=PRODUCT_ID&limit=1` with an existing published product ID. This is a read-only request. Use the store’s [sitemap](https://saccityautoparts.com/sitemap.xml) and product pages to discover products; do not invent product IDs.

The documented discovery and recommendations operations require no account, API key or token. Check HTTP status and JSON errors. Recommendations errors contain status, message and description. JSON-RPC can return an error object even with HTTP 200. Supply the missing/invalid parameter or use the current tool schema before retrying; honor 429 and Retry-After when present.

## Permissions and testing

Shopify publishes [protected-resource metadata](https://saccityautoparts.com/.well-known/oauth-protected-resource) and [authorization-server metadata](https://saccityautoparts.com/.well-known/oauth-authorization-server). Request only the permissions required by the integration. Supported scope names do not confer access. Customer authorization and UCP agent authentication are distinct; follow [Shopify’s authentication documentation](https://shopify.dev/docs/agents/get-started/authentication).

The public quickstarts and [downloadable read-only CLI](https://saccityautoparts.com/downloads/sac-city-agent-cli-1.0.0.tgz) do not create carts, orders or payments. There is no Sac City checkout sandbox or self-serve key issuer on this site. [Mock.shop](https://mock.shop) provides separate synthetic Shopify data for development. The native Shopify MCP services and Markdown negotiation are managed by Shopify.

## Business identity and policies

- [About Sac City Auto Parts](https://saccityautoparts.com/pages/about)
- [Contact](https://saccityautoparts.com/pages/contact): +1 916-463-9111; Info@SacCityAutoParts.com
- Public business address: 3701 Recycle Road, Rancho Cordova, CA 95742, United States
- [Instagram @SacCityAutoParts](https://www.instagram.com/saccityautoparts/)
- [Privacy](https://saccityautoparts.com/policies/privacy-policy), [shipping](https://saccityautoparts.com/policies/shipping-policy), [refunds](https://saccityautoparts.com/policies/refund-policy), [terms](https://saccityautoparts.com/policies/terms-of-service)

Use current product and policy pages as the source of truth. This file supplements Shopify’s native [agents.md](https://saccityautoparts.com/agents.md) and [llms.txt](https://saccityautoparts.com/llms.txt); it does not replace their platform-provided content.