For usage documentation please visit https://doc.babylonjs.com/how_to/debug_layer.
To install using npm :
npm install --save-dev @babylonjs/core @babylonjs/inspector
Afterwards it can be imported to your project using:
import "@babylonjs/core/Debug/debugLayer";
import "@babylonjs/inspector";
The first line will ensure you can access the property debugLayer of the scene while the second will ensure the inspector can be used within your scene.
This is a great example where code splitting or conditional loading could be used to ensure you are not delivering the inspector if not part of your final app.
For more information you can have a look at our ES6 dedicated documentation.