Check that the React Native development environment is ready for testing. Reports status for each subsystem and suggests fixes for any issues found.
| Subsystem | What it checks | Source |
|---|
| Metro | Running? Which port? | cdp_status |
| CDP | Connected to Hermes? Which device/page? | cdp_status |
| App | Platform, RN version, Hermes enabled, screen dimensions | cdp_status |
| Capabilities | Network domain available? Fiber tree accessible? | cdp_status |
| Errors | Active error count, RedBox showing, debugger paused? | cdp_status |
| agent-device | CLI installed? Devices available? | device_list |
| Status | Suggested fix |
|---|
| Metro not found | npx expo start or npx react-native start |
| No Hermes target | Open the app on the simulator |
| CDP code 1006 | Close React Native DevTools, Flipper, or Chrome DevTools |
| hasRedBox: true | Run /rn-dev-agent:debug-screen |
| isPaused: true | Remove debugger; statements or use cdp_reload |
| fiberTree: false | Only works in __DEV__ builds with Hermes |
| agent-device not found | npm install -g agent-device |
| No devices | Boot a simulator: xcrun simctl boot "iPhone 16" |
- Before starting a feature development session
- When other commands report connection issues
- After restarting Metro or the simulator