A broken link is a hyperlink that no longer points to a working destination — typically returning a 404 (not found), 410 (gone), 500 (server error), or DNS-resolution failure. Broken links degrade user experience and SEO.
Broken links accumulate naturally: third-party sites move content, internal pages get renamed without redirects, products get discontinued. A typical mid-size site (5000 pages) accrues hundreds of broken links per quarter without active monitoring.
Link checkers crawl the site, follow every `<a href>`, and verify the destination returns a 2xx or 3xx status within an acceptable time. Soft 404s (pages that return 200 OK but display 'not found' content) are detected by analysing the response body.
Google explicitly considers broken outbound links a quality signal — too many and the page is downranked. Broken internal links also waste crawl budget, leak PageRank into dead ends, and frustrate users into bouncing. Regular monitoring is cheap insurance.
See it in the product: Broken link checker.