expo config

The expo config command displays your project’s resolved Expo configuration, showing how app.json, app.config.js, and environment variables combine into the final configuration used by Expo.

Usage

npx expo config [directory] [options]

Arguments

Options

--type

string

Type of configuration to show. Alias: -tOptions:

public - Public configuration exposed to JavaScript code
prebuild - Configuration used during prebuild
introspect - Full configuration with all fields (default)

--full

boolean

Include all project config data, including defaults and computed values.

--json

boolean

Output configuration in JSON format. Useful for scripting and automation.

What It Shows

The expo config command displays:

Configuration from app.json or app.config.js
Applied config plugins and their modifications
Environment-specific values
Computed default values
Platform-specific settings

Examples

View Full Configuration

Show the complete resolved configuration:

npx expo config

Output example:

{
  "name": "My App",
  "slug": "my-app",
  "version": "1.0.0",
  "orientation": "portrait",
  "icon": "./assets/icon.png",
  "splash": {
    "image": "./assets/splash.png",
    "resizeMode": "contain",
    "backgroundColor": "#ffffff"
  },
  "ios": {
    "bundleIdentifier": "com.mycompany.myapp",
    "buildNumber": "1"
  },
  "android": {
    "package": "com.mycompany.myapp",
    "versionCode": 1
  }
}

JSON Output

Get machine-readable JSON:

npx expo config --json

Perfect for:

CI/CD scripts
Parsing with jq or other tools
Automation workflows

Public Configuration

Show only configuration exposed to your JavaScript code:

npx expo config --type public

This is the configuration available via:

import Constants from 'expo-constants';
console.log(Constants.expoConfig);

Prebuild Configuration

Show configuration used during expo prebuild:

npx expo config --type prebuild

Includes native configuration and config plugin results.

Full Details

Show all configuration including defaults:

npx expo config --full

This displays:

Explicit configuration from your config file
Default values applied by Expo
Computed values based on other settings
All plugin modifications

Specific Project Directory

View config for a specific project:

npx expo config ./my-app

Configuration Types

Introspect (Default)

Shows the complete configuration after:

Reading app.json or app.config.js
Applying config plugins
Merging environment variables
Computing dynamic values

Public

Shows only values exposed to JavaScript runtime:

Available in expo-constants
Embedded in app bundles
Accessible at runtime
Excludes secrets and build-time values

Prebuild

Shows configuration used when generating native projects:

Native identifiers (bundle ID, package name)
Config plugin results
Platform-specific settings
Build-time configuration

Common Use Cases

Debugging Configuration Issues

Check what config is actually being used:

npx expo config --full

Look for:

Unexpected default values
Missing configuration
Plugin modifications
Environment variable substitution

Verifying Environment Variables

Check if environment variables are applied:

EXPO_PUBLIC_API_URL=https://api.example.com npx expo config --json | grep API_URL

CI/CD Validation

Validate configuration in CI:

npx expo config --json > config-output.json

Parse and validate specific fields:

npx expo config --json | jq '.ios.bundleIdentifier'

Comparing Environments

Compare development and production configs:

ENV=development npx expo config --json > dev-config.json
ENV=production npx expo config --json > prod-config.json
diff dev-config.json prod-config.json

Checking Plugin Effects

See what config plugins have modified:

npx expo config --type prebuild

Look for fields modified by plugins like:

Permissions and entitlements
App capabilities
Build settings
Manifest entries

Configuration Files

app.json

Static JSON configuration:

{
  "expo": {
    "name": "My App",
    "slug": "my-app",
    "version": "1.0.0",
    "ios": {
      "bundleIdentifier": "com.mycompany.myapp"
    },
    "android": {
      "package": "com.mycompany.myapp"
    }
  }
}

app.config.js

Dynamic JavaScript configuration:

export default {
  name: "My App",
  slug: "my-app",
  version: process.env.APP_VERSION || "1.0.0",
  ios: {
    bundleIdentifier: "com.mycompany.myapp"
  },
  android: {
    package: "com.mycompany.myapp"
  },
  extra: {
    apiUrl: process.env.API_URL
  }
};

app.config.ts

TypeScript configuration with type checking:

import { ExpoConfig } from 'expo/config';

const config: ExpoConfig = {
  name: "My App",
  slug: "my-app",
  version: "1.0.0",
  ios: {
    bundleIdentifier: "com.mycompany.myapp"
  },
  android: {
    package: "com.mycompany.myapp"
  }
};

export default config;

Environment Variables

Build-Time Variables

Available during configuration:

export default {
  name: process.env.APP_NAME,
  extra: {
    apiUrl: process.env.API_URL
  }
};

Check resolved values:

APP_NAME="My App" API_URL="https://api.example.com" npx expo config

Public Variables

Variables prefixed with EXPO_PUBLIC_ are available at runtime:

// app.config.js
export default {
  extra: {
    apiUrl: process.env.EXPO_PUBLIC_API_URL
  }
};

Access in code:

import Constants from 'expo-constants';
const apiUrl = Constants.expoConfig.extra.apiUrl;

Parsing Output

With jq

Extract specific fields:

# Get app name
npx expo config --json | jq -r '.name'

# Get iOS bundle identifier
npx expo config --json | jq -r '.ios.bundleIdentifier'

# Get all environment variables
npx expo config --json | jq '.extra'

With grep

Search for specific values:

npx expo config | grep bundleIdentifier
npx expo config | grep -A 5 "ios"

In Scripts

Use in shell scripts:

#!/bin/bash
CONFIG=$(npx expo config --json)
NAME=$(echo $CONFIG | jq -r '.name')
VERSION=$(echo $CONFIG | jq -r '.version')

echo "Building $NAME v$VERSION"

Troubleshooting

Config File Not Found

If expo config can’t find your config:

Error: No app.json or app.config.js found

Solutions:

Ensure you’re in the project directory
Create app.json or app.config.js
Specify directory: npx expo config ./path/to/project

Invalid Configuration

If config is malformed:

Error: Invalid Expo config

Check:

JSON syntax in app.json
JavaScript syntax in app.config.js
Required fields (name, slug)
Type errors in app.config.ts

Environment Variables Not Applied

If environment variables aren’t showing:

# Ensure variables are set before command
API_URL=https://api.example.com npx expo config

For .env files, they’re loaded automatically when running Expo commands.

Plugin Errors

If config plugins fail:

Error: Config plugin failed

Check:

Plugin is installed: npm install plugin-name
Plugin syntax in app.json
Plugin compatibility with Expo SDK version

Configuration Schema

The configuration follows a strict schema. To see all available fields:

Expo Config Reference
TypeScript types: expo/config package
JSON schema: Available via Expo API

Best Practices

Version Control

Commit your configuration:

git add app.json app.config.js
git commit -m "Update app configuration"

Environment-Specific Configs

Use environment variables for differences:

const IS_PROD = process.env.ENV === 'production';

export default {
  name: IS_PROD ? 'My App' : 'My App (Dev)',
  slug: 'my-app',
  extra: {
    apiUrl: IS_PROD 
      ? 'https://api.example.com'
      : 'https://dev.api.example.com'
  }
};

Validate in CI

Add validation to your CI pipeline:

- name: Validate config
  run: |
    npx expo config --json > /dev/null || exit 1

Document Custom Fields

Add comments to explain custom configuration:

export default {
  name: "My App",
  // Custom field for internal tools
  extra: {
    internalId: "app-123",
    featureFlags: {
      newFeature: true
    }
  }
};

Overview

Commands

Configuration

​Usage

​Arguments

​Options

​What It Shows

​Examples

​View Full Configuration

​JSON Output

​Public Configuration

​Prebuild Configuration

​Full Details

​Specific Project Directory

​Configuration Types

​Introspect (Default)

​Public

​Prebuild

​Common Use Cases

​Debugging Configuration Issues

​Verifying Environment Variables

​CI/CD Validation

​Comparing Environments

​Checking Plugin Effects

​Configuration Files

​app.json

​app.config.js

​app.config.ts

​Environment Variables

​Build-Time Variables

​Public Variables

​Parsing Output

​With jq

​With grep

​In Scripts

​Troubleshooting

​Config File Not Found

​Invalid Configuration

​Environment Variables Not Applied

​Plugin Errors

​Configuration Schema

​Best Practices

​Version Control

​Environment-Specific Configs

​Validate in CI

​Document Custom Fields