Chrome: Bookmark Sentry, a free Chrome extension, takes the hard work out of checking your bookmark file for bad links and duplicates. Install it, forget about it, and get scheduled reports on the state of your bookmarks file.
It’s that simple. Once you install the extension, open the options to toggle some basic settings to your liking (like the frequency of the scan, how long you want it to wait for a response, and whether you want it to look for bad links and/or duplicates).
Once it finishes scanning you’ll get a report indicating the status of the links (why they are marked as missing or duped) and the ability to selectively or mass delete them. The only caveat we’d share is that it will tell you links behind any sort of security are unavailable. If you bookmark pages that you use for work, behind your corporate firewall for example, if the scanner runs when you’re not authenticated then it won’t be able to reach them. Other than that, it works like a charm.
Bookmark Sentry is free, Google Chrome only.
Update: Do NOT install this extension. It’s bundling ads into your browser.