> Portal Navigation:
> 
> - Append `.md` to any URL under `https://dev.wix.com/docs/` to get its markdown version.
> - Pages are either content pages (article or reference text) or menu pages (a list of links to child pages).
> - To get a menu page, truncate any URL to a parent path and append `.md` (e.g. `https://dev.wix.com/docs/sdk.md`, `https://dev.wix.com/docs/sdk/core-modules.md`).
> - Top-level index of all portals: https://dev.wix.com/docs/llms.txt
> - Full concatenated docs: https://dev.wix.com/docs/llms-full.txt

## Resource: Service Plugins

## Namespace: ecom-catalog

## Article: Introduction

## Article Link: https://dev.wix.com/docs/velo/events-service-plugins/e-commerce/service-plugins/ecom-catalog/introduction.md

## Article Content:

# Introduction
> **Note:** This service plugin is currently in beta and is subject to change. Some service plugins are currently not available to all users.

The eCommerce Catalog service plugin (formerly SPI) is a service provider interface that provides functionality for implementing your own custom catalog of items and/or services to be sold on your site.
Define how your custom catalog interacts with the eCommerce purchase flow in a way that is not currently supported natively by Wix. For example, you can determine the number of 
catalogs to choose from, provide a simplified catalog of products or services, and choose the products or services you wish to sell. The custom catalog can be used instead of, 
or alongside, a Wix Stores catalog.

Wix eCommerce calls the service plugin endpoint [`getCatalogItems()`](#getcatalogitems) to retrieve the custom catalog's items. These items can then be displayed in dynamic product pages,
as well as the cart, checkout, and order.

Learn more:
 + [Custom Catalog Service Plugin](https://support.wix.com/en/article/velo-tutorial-ecommerce-custom-catalog-extension-beta).
 + [Velo: Custom App Extensions Using Service Plugins](https://support.wix.com/en/article/velo-custom-business-app-extensions-using-spis-beta)

### To add a service plugin
1. [Add the plugin to your site](https://dev.wix.com/docs/develop-websites/articles/coding-with-velo/integrations/custom-extensions-spis/custom-app-extensions-using-sp-is.md#step-1-create-a-new-extension-on-your-wix-site).
2. Update the [`getConfig()`](https://www.wix.com/velo/reference/spis/wix-ecom/ecom-catalog/getconfig) function in the **-config.js** file that is added to your site during step 1.
3. Update the [`getCatalogItems()`](https://www.wix.com/velo/reference/spis/wix-ecom/ecom-catalog/getcatalogitems) function in the **.js** file that is added to your site during step 1.