Chrome: Manually checking your bookmarks file is an extremely low priority for most people, but it's irritating to find out the link you need is dead. Bookmark Sentry scans your bookmarks and displays the dead links and dupes for easy deletion.
Bookmark Sentry is a simple Chrome extension that sits in the background, scanning your bookmarks file at intervals you specify. Bookmark Sentry scans your bookmarks file and finds problems (such as connection errors, 404 errors, and more) as well as duplicates within your bookmark structure. From the Bookmark Sentry report screen you can delete the files or click on the link to verify the link is dead before deletion.
Bookmarks Sentry is a free extension and works wherever Google Chrome does. Firefox users who want similar functionality should check out previously reviewed Incredible Bookmarks.