An app extension enables you to add your app's functionality to Shopify user interfaces. This guide introduces app extensions and how they work.
## How it works
An app extension surfaces the functionality of your app where and when users need it most. App extensions are useful for apps that require quick, frequent actions from users.
For example, your app’s actions can appear as dropdown items in Shopify admin for orders, products, customers, and other resources. You can produce interfaces that easily mimic the Shopify look-and-feel, and make your app seamlessly appear in Shopify Point of Sale (POS).
### Without an app extension
Without an app extension, users interact directly with your app. Your app relays information to Shopify that gets surfaced back to the users through your app:
### With an app extension
With an app extension, users interact with Shopify. Shopify relays information to your app that gets surfaced back to the users through your app extension in Shopify:
> Note:
> An app extension isn’t an app. It's a mechanism that lets an app add features to certain defined parts of several Shopify user interfaces. Apps that use extensions must adhere to the same [authentication requirements](/docs/apps/build/authentication-authorization) and [rate limits](/docs/api/usage/rate-limits) as apps that don’t use extensions.
## Creating app extensions
You can create app extensions using [Shopify CLI](/docs/apps/build/cli-for-apps) or the [Partner Dashboard](https://partners.shopify.com/current/apps). The tool that you use to create an app extension depends on the type of extension that you're building. To learn which tool to use to create each extension type, refer to the [list of extension types](/docs/apps/build/app-extensions/list-of-app-extensions).
For information about building and previewing app extensions, refer to the documentation for your extension type.
### Extension-only apps
Extension-only apps are apps that don't have embedded app pages. Because they're made up entirely of extensions, you can host extension-only apps on Shopify.
> Note:
> Extension-only apps can only be installed with [custom distribution](https://shopify.dev/docs/apps/launch/distribution/select-distribution-method).
[Learn about extension-only apps that don't require a web server](/docs/apps/build/app-extensions/build-extension-only-app).
## Configuring app extensions
When you [generate an app extension](/docs/api/shopify-cli/app/app-generate-extension), a TOML configuration file named `shopify.extension.toml` is automatically generated in your app's extension directory. The TOML file is located in the [`extensions/` directory](/docs/apps/build/cli-for-apps/app-structure#directory-structure) of your app project.
For information about the properties that you can configure in the TOML file, refer to [Configuring app extensions](/docs/apps/build/app-extensions/configure-app-extensions).
## Versioning and deployment
Your app configuration and all extensions, including extensions created in the Partner Dashboard, are versioned together as a single [app version](/docs/apps/launch/deployment/app-versions).
When you run the [`deploy` command](/docs/api/shopify-cli/app/app-deploy) using [Shopify CLI](/docs/api/shopify-cli), an app version is created and released. You can revert to a previous app version at any time. You can also create an app version from the Partner Dashboard.
Releasing an app version replaces the current active version that's served to stores that have your app installed. It might take several minutes for app users to be upgraded to the new version.
[Learn how to deploy extensions](/docs/apps/launch/deployment/deploy-app-versions).
## Reviews and approvals
Some app extensions need to be reviewed and approved before they're released to users.
If an app extension needs to be reviewed, then you can't release the related app version until you [submit it for review](/docs/apps/launch/deployment/deploy-app-versions#submit-an-app-version-for-review) and it's been approved.
To learn whether your extension type needs to be reviewed, refer to the [list of extension types](/docs/apps/build/app-extensions/list-of-app-extensions).
## Removing app extensions
If you no longer want users to use an app extension, or you want to temporarily disable an app extension, then you can remove it.
[Learn how to remove an app extension from your app](/docs/apps/build/app-extensions/remove-app-extension).
## Developer tools and resources
## Next steps
- Consult the [list of app extensions](/docs/apps/build/app-extensions/list-of-app-extensions) to determine which app extensions are versioned, which app extensions require reviews and approvals, where you manage the app extensions in Shopify, and more.
