When You Need The XLabs App
You need the XLabs app when a lab or challenge runs locally on your machine. The app connects the browser to local Docker-based lab environments.
Theory quiz labs do not require the XLabs app.
If a lab only asks you to read scenarios and take quizzes, you can complete it without local setup. If a lab opens a terminal environment, local execution usually needs Docker and the XLabs app.
Docker Desktop Requirement
For local terminal labs, Docker Desktop must be installed and running before starting the lab.
Having the docker command installed is not enough. The Docker daemon must also be available.
A quick check is to run docker run --rm hello-world from your terminal. If that works, Docker is running and reachable from your machine.
Local And Cloud Execution
Local execution runs the environment on your machine. Cloud execution starts a hosted environment when available.
Use local execution when your XLabs app and Docker setup are working. Use cloud execution when you cannot run Docker locally or are using a locked-down device.
Before Starting A Terminal Lab
Before starting a terminal-heavy lab, check that Docker Desktop is running and the XLabs app is open.
If you started XLabs before Docker was ready, restart XLabs after Docker becomes available. This prevents the browser from trying to connect to an agent that cannot create lab containers yet.