When developing or debugging Pluto, it can be very useful to check the browser developer tools. This is how you do it:
Now that you have the panel open, you need to open the Console tab in this panel. It should look like this:
To make sure you found it, check for the message "Pluto.jl, by..."
If something goes wrong, you will probably see a message in red, which is not supposed to happen. Take a screenshot!