> 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: About Service Plugins

## Article: About Service Plugins

## Article Link: https://dev.wix.com/docs/studio-two/code-your-site/build-a-custom-backend/service-plugins/about-service-plugins.md

## Article Content:

# About Service Plugins

A [service plugin](https://dev.wix.com/docs/overview/extensions-framework/backend-extensions/service-plugins.md) is custom backend logic that Wix calls during one of its own flows, such as checkout or booking. In Studio Two you add one from the **Code** tab through the **Wix Extension Builder**, and the plugin is part of the site project.

Studio Two uses the SDK service plugins that the **Wix Extension Builder** offers. Wix Studio and Wix Editor sites use Velo service plugins, and that set is smaller. For the full list and for what each plugin's handler must return, see [Available Service Plugins](https://dev.wix.com/docs/backend-extensions/service-plugins/available-service-plugins.md).

## Anatomy of a service plugin

A service plugin in a Studio Two project is a configuration file and a handler:

- The **handler** is the code Wix calls. It receives the current cart, booking, or other host state, and returns a response in the shape that plugin requires.
- The **configuration file** declares the plugin's ID, name, and path to the handler. For the fields, see [Service Plugin Extension Files and Code](https://dev.wix.com/docs/backend-extensions/service-plugins/service-plugin-extension-files-and-code.md).

You generate the files first, then edit the handler. For that workflow, see [Build a Service Plugin in Studio Two](https://dev.wix.com/docs/studio-two/code-your-site/build-a-custom-backend/service-plugins/build-a-service-plugin-in-studio-two.md).

## How service plugins are used

- You add the plugin from the **Code** tab through the **Wix Extension Builder**, which puts its files in your site project and registers it.
- You pick the plugin type from a fixed list, such as **Ecom Additional Fees** or **Booking Policy Provider**.
- Wix calls the handler when the matching flow runs on the site. Calling the underlying API yourself doesn't reach the handler.

## See also

- [Add a Service Plugin Extension in Studio Two](https://dev.wix.com/docs/studio-two/code-your-site/build-a-custom-backend/service-plugins/add-a-service-plugin-extension-in-studio-two.md)
- [Build a Service Plugin in Studio Two](https://dev.wix.com/docs/studio-two/code-your-site/build-a-custom-backend/service-plugins/build-a-service-plugin-in-studio-two.md)
- [Service Plugins](https://dev.wix.com/docs/overview/extensions-framework/backend-extensions/service-plugins.md)
- [Custom Business Logic](https://dev.wix.com/docs/overview/backend-services/custom-business-logic.md)
- [Available Service Plugins](https://dev.wix.com/docs/backend-extensions/service-plugins/available-service-plugins.md)
- [Service Plugin Extension Files and Code](https://dev.wix.com/docs/backend-extensions/service-plugins/service-plugin-extension-files-and-code.md)