No authority score is a metric Google itself publishes or uses; each one (Moz's Domain Authority, Ahrefs' Domain Rating, Semrush's Authority Score) is a proprietary formula built by a different SEO tool vendor, trained mostly on the quantity and quality of a site's backlinks. That makes these scores useful as a directional comparison — is Site A probably stronger than Site B — but risky to treat as a target in themselves, since chasing a higher score doesn't reliably cause higher rankings, and the underlying formulas change without notice. The more reliable use of an authority score is competitive triage: quickly sorting a list of potential link targets or competitors by rough strength before doing deeper keyword-level analysis.
Example
An SEO team uses Authority Score to shortlist 40 potential guest-post targets down to the dozen worth manually reviewing for topical relevance.
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