> ## Documentation Index
> Fetch the complete documentation index at: https://mintlify.com/expo/expo/llms.txt
> Use this file to discover all available pages before exploring further.

# expo start

> Start a local development server for your Expo app.

The `expo start` command launches a local development server with Metro bundler, enabling you to develop your app on iOS, Android, and web platforms simultaneously.

## Usage

```bash theme={null}
npx expo start [directory] [options]
```

## Arguments

<ParamField path="directory" type="string">
  Directory of the Expo project. Defaults to the current working directory.
</ParamField>

## Options

### Platform Selection

<ParamField path="--android" type="boolean">
  Open the app on a connected Android device or emulator. Alias: `-a`
</ParamField>

<ParamField path="--ios" type="boolean">
  Open the app in an iOS simulator. Alias: `-i`
</ParamField>

<ParamField path="--web" type="boolean">
  Open the app in a web browser. Alias: `-w`
</ParamField>

### Development Client Options

<ParamField path="--dev-client" type="boolean">
  Launch the app in a custom native development build. Alias: `-d`
</ParamField>

<ParamField path="--go" type="boolean">
  Launch the app in Expo Go. Alias: `-g`
</ParamField>

### Bundler Options

<ParamField path="--clear" type="boolean">
  Clear the Metro bundler cache before starting. Alias: `-c`, `--reset-cache`
</ParamField>

<ParamField path="--max-workers" type="number">
  Maximum number of tasks to allow Metro to spawn. Useful for controlling CPU usage.
</ParamField>

<ParamField path="--no-dev" type="boolean">
  Bundle in production mode instead of development mode.
</ParamField>

<ParamField path="--minify" type="boolean">
  Minify JavaScript code. Typically used with `--no-dev` for production testing.
</ParamField>

### Network Options

<ParamField path="--host" type="string">
  Dev server hosting type. Alias: `-m`

  Options:

  * `lan` - Use the local network (default)
  * `tunnel` - Use any network by tunneling through ngrok
  * `localhost` - Connect over localhost only
</ParamField>

<ParamField path="--tunnel" type="boolean">
  Same as `--host tunnel`. Enables remote access via ngrok.
</ParamField>

<ParamField path="--lan" type="boolean">
  Same as `--host lan`. Uses your local network IP address.
</ParamField>

<ParamField path="--localhost" type="boolean">
  Same as `--host localhost`. Only accessible from the same machine.
</ParamField>

<ParamField path="--port" type="number">
  Port to start the dev server on. Defaults to 8081. Does not apply to web or tunnel. Alias: `-p`
</ParamField>

<ParamField path="--offline" type="boolean">
  Skip network requests and use anonymous manifest signatures. Useful for development without internet.
</ParamField>

### Advanced Options

<ParamField path="--scheme" type="string">
  Custom URI protocol to use when launching the app. Overrides the scheme in app.json.
</ParamField>

<ParamField path="--https" type="boolean">
  Start the dev server with HTTPS protocol. **Deprecated in favor of `--tunnel`**.
</ParamField>

<ParamField path="--private-key-path" type="string">
  Path to private key for code signing. Defaults to `private-key.pem` in the same directory as the certificate specified by expo-updates configuration in app.json.
</ParamField>

## Examples

### Basic Development

Start the development server with default settings:

```bash theme={null}
npx expo start
```

This starts Metro bundler and shows an interactive terminal UI with:

* QR code for Expo Go
* Options to open on different platforms
* Keyboard shortcuts for common actions

### Launch on Specific Platform

Open directly on iOS simulator:

```bash theme={null}
npx expo start --ios
```

Open on Android emulator:

```bash theme={null}
npx expo start --android
```

Open in web browser:

```bash theme={null}
npx expo start --web
```

### Multiple Platforms

Launch on multiple platforms simultaneously:

```bash theme={null}
npx expo start --ios --android --web
```

### Development Client

For custom development builds:

```bash theme={null}
npx expo start --dev-client
```

### Clear Cache

If you're experiencing issues, clear the bundler cache:

```bash theme={null}
npx expo start --clear
```

Or use the alias:

```bash theme={null}
npx expo start -c
```

### Production Mode

Test production bundling locally:

```bash theme={null}
npx expo start --no-dev --minify
```

### Custom Port

Run on a different port:

```bash theme={null}
npx expo start --port 8000
```

### Tunnel for Remote Access

Share your development server over the internet:

```bash theme={null}
npx expo start --tunnel
```

This is useful for:

* Testing on physical devices without being on the same network
* Sharing with team members
* Testing from different locations

### Localhost Only

Restrict access to localhost:

```bash theme={null}
npx expo start --localhost
```

### Offline Development

Work without an internet connection:

```bash theme={null}
npx expo start --offline
```

### Limit CPU Usage

Control Metro's resource consumption:

```bash theme={null}
npx expo start --max-workers 2
```

## Interactive Commands

While the dev server is running, you can press these keys:

* **a** - Open on Android
* **i** - Open on iOS
* **w** - Open on web
* **r** - Reload app
* **m** - Toggle menu
* **j** - Open debugger
* **o** - Open project in editor
* **c** - Clear cache and restart
* **?** - Show help

## Environment Variables

The `expo start` command respects several environment variables:

* `PORT` - Default port for the dev server
* `EXPO_DEVTOOLS_LISTEN_ADDRESS` - Address to bind the dev server
* `EXPO_DEBUG=1` - Enable debug logging
* `EXPO_OFFLINE=1` - Start in offline mode
* `CI=1` - Run in non-interactive CI mode
* `EXPO_NO_CACHE=1` - Disable API caches

## How It Works

When you run `expo start`:

1. **Loads Configuration** - Reads app.json or app.config.js
2. **Starts Metro Bundler** - Initializes the JavaScript bundler
3. **Creates Dev Server** - Sets up HTTP server with middleware
4. **Generates Manifest** - Creates the Expo manifest for runtime
5. **Displays UI** - Shows QR code and interactive terminal
6. **Watches Files** - Monitors for changes and triggers hot reloads

## Platform-Specific Behavior

### iOS

* Automatically detects running simulators
* Can launch new simulator if none are running
* Supports both Expo Go and development builds
* Handles code signing for development certificates

### Android

* Detects connected devices via ADB
* Can launch emulators if none are running
* Installs APK if not present
* Forwards port for device communication

### Web

* Uses Metro bundler (not Webpack)
* Supports server-side rendering
* Handles static file serving
* Includes React Native Web shims

## Troubleshooting

### Port Already in Use

If port 8081 is busy:

```bash theme={null}
npx expo start --port 8082
```

Or kill the process using the port:

```bash theme={null}
# macOS/Linux
lsof -ti:8081 | xargs kill -9

# Windows
netstat -ano | findstr :8081
taskkill /PID <PID> /F
```

### Cache Issues

Clear the cache if you see stale code:

```bash theme={null}
npx expo start --clear
```

### Network Connection Issues

If QR code doesn't work:

1. Ensure both computer and device are on same network
2. Check firewall settings
3. Try `--tunnel` mode
4. Use `--localhost` and connect via USB

### Metro Bundler Errors

If Metro fails to start:

```bash theme={null}
# Clear watchman cache (macOS)
watchman watch-del-all

# Clear Metro cache
npx expo start --clear

# Clear node_modules
rm -rf node_modules
npm install
```