A hundred links from five sites is weaker than fifty links from forty sites. The free Backlink Source Diversity Comparator puts your link profile next to a competitor's and measures how widely each one is really spread.
Paste both backlink exports, one link per line as URL | anchor. The tool counts unique domains and TLDs, measures how much of each profile the top one and top five domains control, scores diversity from 0 to 100, and lists the exact gap domains that link to your rival but not to you.
Diversity is the quiet ranking factor behind resilient sites. Compare profiles quarterly and close the gaps before a competitor widens them.