Troubleshooting

Every failure says so, either in Metro's output or in the DevTools console.

React Native DevTools was not found

[devtools] React Native DevTools was not found, so no tab is served.

The helper could not resolve @react-native/debugger-frontend from your project. A monorepo that hoists oddly is the usual cause, and frontendPath is the way out.

Ask your project for the path. The package's entry point exports it as a string, so this prints it:

node -p "require('@react-native/debugger-frontend')"

Run that from your app's directory, and hand the result over:

module.exports = withReactNativeDevtoolsTab(getDefaultConfig(__dirname), {
  frontendPath:
    "/your/app/node_modules/@react-native/debugger-frontend/dist/third-party/front_end",
});

Note how deep it sits. It is the directory the files are actually in, several levels below the package root, not the package root itself. ls it and you should see rn_fusebox.html, which is the page DevTools opens. If the node -p fails too, the package is genuinely not installed where your app can see it, and the fix is the install rather than this option.

Could not point the debugger shortcut at the tab

[devtools] could not point the debugger shortcut at the tab.

The frontend was found but @react-native/dev-middleware was not, so DevTools opens on its own route with no tab script in it. Two copies of that package in one install is the usual reason.

The app never installed its devtools dispatcher

[devtools] the app never installed its devtools dispatcher

Printed in the DevTools console after ten seconds of asking. The panel is up and the app is not answering, so either the app's bundle never pulled this package in, or it did so behind a __DEV__ guard in a build where that is false.

Nothing printed at all

Metro was not restarted after the config changed.