Click the "Links" button on the upper content-spanning toolbar to display the menu, and then select "Validate Links".
CommonSpot will scan the page checking for the reachability of links other than jumps internal to the page, and images, and will report on what it finds.
CommonSpot can only tell you whether a page was found, or not. It cannot tell you whether the intended page was found!
CommonSpot will not even try to follow secure links (those that start https://), although it will check them for syntax correctness.
CommonSpot will not even try to follow mailto links, but it will check them for syntax correctness if they don't include the optional pre-loading of the subject text.