Config Plugin

The config plugin integrates with expo prebuild and EAS Build so that flags are set at native build time.

What it does

When a native build runs, the config plugin will:

1. Read EXPO_BUILD_FLAGS from the environment (comma-separated flag names)
2. Generate the runtime buildFlags.ts module with those flags enabled
3. Add an EXBuildFlags array to Info.plist (iOS)
4. Add a <meta-data android:name="EXBuildFlags"> tag to AndroidManifest.xml (Android)

The native metadata is informational — it lets you inspect which flags a given binary was built with. A convenience API for reading these values from native code is a planned goal.

Setup

1. Add the plugin to app.json

   app.json

   {
     "expo": {
       "plugins": ["expo-build-flags"]
     }
   }

2. Set flags in your EAS build profile

   eas.json

   {
     "build": {
       "staging": {
         "env": {
           "EXPO_BUILD_FLAGS": "newCheckout,betaDashboard"
         }
       }
     }
   }

3. Build

   eas build --profile staging

   The generated buildFlags.ts will have newCheckout and betaDashboard set to true.

Skipping the CLI in EAS

If you run build-flags override in a postinstall script (as recommended in the Quick Start), you’ll want to skip it during EAS builds since the config plugin already handles generation. Use --skip-if-env:

package.json

{
  "scripts": {
    "postinstall": "build-flags override --skip-if-env EAS_BUILD"
  }
}

When EAS_BUILD is set (which EAS does automatically), the override command is a no-op. You can reference any CI var name here (not value).