Backlink index

A backlink index is a large database built by a tool crawling the web and recording which pages link to which others. You enter your own or a competitor's domain and see who links to it, which pages attract links, the text used in the links and how strong the linking sites look. Ahrefs and SEMrush are listed as tools with a backlink index. No index covers every link, so results differ between tools.

Links from other sites are one of the signals search engines use to judge how trustworthy a page is. Seeing a competitor's links shows you where to look for coverage, partnerships or directories that could link to you too. It also helps you spot harmful or spammy links. The feature matters if search traffic is important and you compete for competitive terms. It matters less for a local business with little competition, or for one whose customers come mainly from referrals and outbound work.

• How large is the index, and how often is it refreshed.
• Can you see new and lost links over time, not only a snapshot.
• Is the data limited by plan, for example in rows per report or reports per day.
• Run the same competitor domain in two tools and compare how many links each one finds.