Our Methodology

• Ahrefs Domain Rating (free public endpoint): Ahrefs' real, measured Domain Rating, from their freeapi.ahrefs.com/v3/public/domain-rating-freeendpoint. This requires only a free Ahrefs account API key, no paid subscription. When available, this is the actual DR shown (marked with a "Real" badge) and the base signal DA is derived from (see section 2).
• Moz DA, PA and Spam Score: Moz's own metrics from its official Data API, used only when a Moz API connection is configured and has lookups left. Before each request we check Moz's own zero-cost quota endpoint and only spend rows it confirms are available. Moz values are labeled Moz; everything else falls back to the DR-derived estimate below. At the moment the site has no Moz API connection, so DA, PA and Spam Score are labeled Estimated.
• Open PageRank: a free API providing a 0-10, PageRank-style authority score per domain. Used as the fallback signal behind DA and PA whenever real Ahrefs/Moz data isn't available for a domain (not covered, no key configured, or monthly cap reached).
• RDAP: the modern, standardized successor to WHOIS, used to determine domain registration/creation date where available.
• Wayback Machine (Internet Archive): used only when the registry publishes no registration date (some ccTLDs, such as .so and .pk, have no RDAP service). The age is then labeled "First archived" with the capture date, since it shows when the site first appeared online, not when the domain was registered.
• Live TLS/SSL check: a direct connection to the domain to verify a valid HTTPS certificate.
• Public DNS blocklists: Spamhaus DBL, queried directly through Spamhaus's own name servers, no API key required. If Spamhaus gives no usable answer (for example its documented "query blocked" response), we show "Check unavailable" instead of claiming the domain is clean.
• DNS resolution: confirms the domain actually resolves (is "live") at check time.

Ahrefs' DR endpoint and Open PageRank both work on free keys within their free limits. Moz data appears only when a Moz API connection is available (see section 2 for exactly how the fallback works).

When a Moz API connection is available and has lookups left, DA (and PA) is Moz's own measured score, labeled Moz. Any domain that gets Moz data is cached for 30 days, so lookups go toward covering more distinct domains rather than repeat checks of the same one.

For every other domain, DA is derived from real Ahrefs DR using a calibrated DR→DA curve (src/lib/daFromDr.ts): DA and DR are both 0-100 logarithmic backlink-strength scores that track each other closely in practice (DA trails DR through the low and mid range and the two converge near the top of the scale), so we interpolate between anchor points calibrated against publicly observable DA/DR pairs for real sites, then apply the same small age/HTTPS/live adjustments used elsewhere. If no real DR is available either, we fall back further to an Open PageRank-based estimate, or a smaller age-and-technical-signal-only score if Open PageRank has no data.

PA comes from the same Moz call as DA, so it's real whenever DA is (marked with the same "Real" badge). Outside the Moz budget, Open PageRank only scores at the domain level (it does not provide a distinct signal per URL), so PA falls back to a disclosed approximation: a small, deterministic adjustment from the domain's (real-DR-derived or estimated) DA, intended to reflect the homepage specifically.

When a domain is covered by Ahrefs' free public DR endpoint, the DR shown is Ahrefs' real, measured Domain Rating (an "Ahrefs" badge marks this in the UI and CSV export). We do not modify that value using HTTPS, availability, age, or another local signal. We never estimate DR. If Ahrefs has no Domain Rating for a domain, or the lookup fails, we show N/A instead of a number.

When Moz data is available, Spam Score is Moz's percentage metric and is labeled Moz. Moz treats 1-30% as low, 31-60% as medium, and 61-100% as high. A high result is a reason to investigate, not proof that a site is spam.

When Moz is unavailable, our Estimated fallback combines these risk points:

• Domain age under 1 year: +6. Under 2 years: +3. Under 3 years: +1.
• Each public DNS blocklist hit: +4, capped at +8 total.
• Missing or invalid HTTPS: +2.
• Domain not currently resolving: +3.
• Statistically higher-risk TLD (e.g. .xyz, .top, .click, .work): +2.

The fallback's 0-17 raw points are normalized to the 0-100 display scale. It is never presented as Moz Spam Score. Lower is safer, but this remains a heuristic risk signal.

Results are cached for up to 12 hours per domain (24 hours for Ahrefs DR, 30 days for Moz DA/PA) to keep the tool fast and to stay within API quotas. Re-checking the same domain within that window returns the same cached result.

Domain Rating by Ahrefs, used under their Domain Rating license. Domain Authority and Page Authority by Moz.

"Domain Authority" is a registered trademark of Moz, Inc. DAPA Checker is an independent tool, not affiliated with, endorsed by, or connected to Moz. Our use of "DA" refers to the general, industry-standard concept of domain-level search authority, calculated with our own methodology described above.