This huge study on link rot shows how fast backlinks are lost. It is based on the monitoring of millions of links over several years.
That is quite a useful stat to know. While your tool looks at the seo perspective for inbound links that break (site owners should really plan ahead and 30x redirect somewhere else) I'm building a simple website toolkit (focusing on wordpress) for the reverse - helping site owners find outbound links that have become broken with a focus on user experience perspective.
Hope your service grows well.