A broken backlink is an incoming link pointing to an “error 404” page of a target website.
Find Broken Backlinks using Broken backlinks report
Within Ahrefs Site Explorer, we have a Broken backlinks report under the Backlinks profile section. It shows all the referring pages that link to 404 pages of a target website along with their anchor and surrounding texts.
You can sort or filter this list of backlinks based on their Anchor text, URL, DR, and more. Multiple filters can be stacked together.
Find Pages with Broken Backlinks using the Best by Links report
Another way to check for pages that are linking to 404 pages of the target website is the Best by links report, under the Pages section. Just apply the “HTTP code: 404 not found” filter.
By clicking on the Links to page dropdown, you can see all the external pages linking to that 404 page.
So that you don’t miss out some valuable “link juice”, it's recommended to restore those broken pages, or use redirects to other relevant pages of your website.
In the same way, you can find your competitors’ broken pages that have lots of backlinks and use it for your broken link building strategy. Just reach out to website owners who link to 404 pages of your competitors and offer your relevant content as a replacement.