Since version 188.8.131.52, you can (manually) check whether a link is alive. To do this, click the small magnifier icon on the right side of the link as it is listed in the Links page. After a few seconds (or less), an icon appears. A green tick means the link is valid. A red sign means the link is broken.
Note: the links checker effectively tries to connect to the given link from the server. As such, a link that works for you might not work for the server, and vice-versa. This will require the server to be equipped with the CURL library. Check with your admin if this is the case.