Here’s a short post but one that I think a few people might find useful: CadSoft EAGLE keyboard commands/shortcuts (strangely found under the “Assign” menu in Eagle) to show and hide the Top and Bottom layers independently. I’ve also got one to show all layers, top and bottom. Note that you can change any key a command is bound to when you set up the “assignment” in Eagle.

To set a shortcut in Eagle, choose Options → Assign…. and press the New button.

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Once in the menu, choose the key you want the assignment to bind to, along with any modifier keys (Alt, Shift, etc). I chose Alt+0 for showing the bottom layer only, Alt+1 for the top layer only, and F12 for all top and bottom layers.

Here’s the three Eagle commands for Top, Bottom, and All layers:

• Top only: display none; display 1 17 18 19 20 21 23 25 27 29 39 41 45 51;
• Bottom only: display none; display 16 17 18 19 20 22 24 26 28 30 40 42 45 52;
• All (Top and Bottom): display none; display 1 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 39 40 41 42 45 51 52;

A bit time consuming to implement, but they’ll save you tons of time once you’re actually doing a layout.