Expo Docs MCP Server

--- title: Add custom native code description: Learn how to add custom native code to your Expo project. --- You can add custom native code by using one or both of the following approaches: - [Using libraries that include native code](#using-libraries-that-include-native-code) - [Writing native code](#writing-native-code) ## Using libraries that include native code Expo and React Native developers typically spend the vast majority of their time writing JavaScript code and using native APIs and components that are made available through libraries like [`expo-camera`](/versions/latest/sdk/camera/), [`react-native-safe-area-context`](/versions/latest/sdk/safe-area-context/), and `react-native` itself. These libraries allow developers to access and use device features from their JavaScript code. They may also provide access to a third-party service SDK that is implemented in native code (such as [`@sentry/react-native`](/guides/using-sentry/), which provides bindings to the Sentry native SDK for Android and iOS). If you are using the sandbox app, [Expo Go](http://expo.dev/go), [you can only access native libraries that are included in the Expo SDK](/versions/latest/sdk/third-party-overview/), or libraries that do not include any custom native code ([learn more](/workflow/using-libraries/#third-party-libraries)). [Creating a development build](/develop/development-builds/introduction/) allows you to change the native code or configuration as you would in any other native app. ### Installing libraries with custom native code in development builds When using [development builds](/develop/development-builds/introduction/), using libraries with custom native code is straightforward: - Install the library with npm, for example: `npx expo install react-native-localize` - If the library includes a [config plugin](/config-plugins/introduction/), you can specify your preferred configuration in your app config. - Create a new development build (either [locally](/guides/local-app-development/) or with [EAS](/develop/development-builds/create-a-build/)). You can now use the library in your application code. [The development overview](/workflow/overview/) provides details on key concepts for developing an app with Expo and the flow of the core development loop. ## Writing native code Use the [Expo Modules API](/modules/overview/) to write Swift and Kotlin code and add new capabilities to your app with native modules and views. While there are other tools that you can use to build native modules, we believe that using the Expo Modules API makes building and maintaining nearly all kinds of React Native modules about as easy as it can be. We think that the Expo Modules API is the best choice for most developers building native modules for their apps. It's common to encounter situations where a library doesn't quite do what you need. For example, the library might not provide access to a specific platform feature, or a third-party service might not provide bindings for React Native. If you intend to write a native module primarily in C++, you may want to explore the [Turbo Modules API](https://github.com/reactwg/react-native-new-architecture/blob/main/docs/turbo-modules.md) provided by React Native. ### Using the Expo Modules API ### Creating a local module If you intend to use your native module in a single app (you can always change your mind later), we recommend [using a "local" Expo module](/modules/get-started/#creating-the-local-expo-module) to write custom native code. Local Expo Modules function similarly to [Expo Modules](/modules/overview) used by library developers and within the Expo SDK, like `expo-camera`, but they are not published on npm. Instead, you create them directly inside your project. Creating a local module scaffolds a Swift and Kotlin module inside the `modules` directory in your project, and these modules are automatically linked to your app. ### Sharing a module with multiple apps If you intend to use your native module with multiple apps, then use `npx create-expo-module@latest,` leave out the `--local` flag, and [create a standalone module](/modules/use-standalone-expo-module-in-your-project/). You can publish your package to npm, or you can put it in a packages directory in your [monorepo](/guides/monorepos/) (if you have one) to use it in [a similar way to local modules](/modules/use-standalone-expo-module-in-your-project/). ## Considerations when using Continuous Native Generation (CNG) The following suggestions are most important when using [CNG](/workflow/continuous-native-generation/), but are good guidelines even if you don't use it. By default, Expo projects created with `create-expo-app` use CNG and do not contain **android** or **ios** native directories until you've run the `npx expo prebuild` command in your project. When using CNG, developers typically do not commit the **android** and **ios** directories to source control and do not generate them locally, since EAS Build will do it automatically during the build process. That said, it is common to generate native directories and build locally with `npx expo run` when writing custom native code, to have a fast feedback loop and full access to native debugging tools in Android Studio / Xcode. If your native code requires that you make changes to your project configuration, such as modifying the project's **AndroidManifest.xml** or **Info.plist**, [you should apply these changes through a config plugin](/modules/config-plugin-and-native-module-tutorial/) rather than by modifying the files directly in the **android** and **ios** directories. Remember that changes made directly to native project directories will be lost the next time you run prebuild when you use CNG. If you need to hook into Android lifecycle events or `AppDelegate` methods, use the APIs provided by Expo Modules for [Android](/modules/android-lifecycle-listeners/) and [iOS](/modules/appdelegate-subscribers/) to accomplish this rather than modifying the source files in your native project directories directly or using a config plugin to add the code, which does not compose well with other plugins.