---
title: iOS App Extensions
description: Learn how to use app extensions with EAS Build to add custom functionality.
---

App extensions let you extend custom functionality and content beyond your app and make it available to users while they're interacting with other apps or iOS system functionality. EAS Build provides affordances for including app extensions in both bare and managed projects.

## Managed projects (experimental support)

A typical, simple managed project we have a single application target and no app extensions. You can add an app extension to your project by writing a [config plugin](/config-plugins/introduction/) (or using a library that creates an extension with its own config plugin). Config plugins let you add targets to the Xcode project that is generated during the "Prebuild" phase of a build job.

Declaring app extensions with `extra.eas.build.experimental.ios.appExtensions` in your app config makes it possible for EAS CLI to know what app extensions exist _before the build starts_ (before the Xcode project has been generated) to ensure that the required credentials are generated and validated. Config plugins are also able to modify the app config, and in most cases, if you are using a library that adds an extension then the config plugin will also add the required configuration to declare the extension in your app config. If you are writing a library, we recommend that you consider this. The following is an example of what this would look like if it were declared directly in **app.json**:

```json app.json
{
  "expo": {
    ...
    "extra": {
      "eas": {
        "build": {
          "experimental": {
            "ios": {
              "appExtensions": [
                {
                  "targetName": "myappextension",
                  "bundleIdentifier": "com.myapp.extension",
                  "entitlements": {
                    "com.apple.example": "entitlement value"
                  }
                }
              }
            ]
          }
        }
      }
    }
  }
```

## Bare projects

When you build a bare project, EAS CLI will automatically detect app extensions configured in your Xcode project and generate all necessary credentials for each target, or you can provide them in **credentials.json** For more information, see [Multi target project](/app-signing/local-credentials/#multi-target-project).
