Linkbot Pro is a link checker and HTML validator from Tetranet Software, who also make Metabot .
Pricing varies by number of users.
Whatever your personal tolerance for imperfection, errata on your Web site can cost you money. They cost you page impressions, customers, and respect. Being careful when you create your pages is a good policy, but no matter what you do, errors will creep in, especially on a large site with several people working on it. It's well worth using a tool like Linkbot to find and fix errors on your site. Linkbot Pro, from Tetranet Software, is a Website testing program that can automatically scan a site for more than fifty potential problems, including bad links, bad HTML, slow-loading pages and more.