Site Strength is our 0–100 estimate of a website's link strength. It looks at how many different websites link to a domain and how much weight those links carry. Use it to decide which competitors or link prospects deserve a closer look. It is not a prediction of where a page will rank.

If your first thought is, “Great, another SEO metric to game,” fair. This industry loves giving old ideas new names. The name is the least interesting part. What matters is whether the data is good enough to base a decision on—and whether we tell you where it falls short.

Illustrated websites sending links toward one domain
The same number of links can mean different things, depending on which websites sent them.

How we build Site Strength

There are several ways to estimate a website's link authority. Ahrefs' Domain Rating starts with the number of unique websites linking to you through links that are not marked nofollow (often called “dofollow” links). It also considers how strong those websites are and how many other domains they link to. DataForSEO's backlink rank is based on referring domains and a link-based ranking method. Both turn that evidence into a score. The details of their indexes and math differ.

Here is our approach. We take links between websites from Common Crawl's published releases. We count distinct referring domains, so a hundred links from one site count as one linking website, not a hundred. We also look at the wider pattern of links: a link from a widely cited site carries more evidence than one from a site with no such connections.

Four links from three websites still means three referring domains. Site Strength also considers how connected those websites are.

We base that part of the math on two published ideas. PageRank (Brin and Page, 1998) passes weight through links, so the source of a link matters. Harmonic centrality (Boldi and Vigna, 2014) captures how connected a website is through paths across the web, including when some sites cannot reach one another. Our current score uses the ordering from both measures, plus the referring-domain count, and maps them to 0–100. Together, these signals tell us more than a simple backlink total.

The systems count different links. Common Crawl includes technical links to images and scripts; Ahrefs excludes nofollow links from DR. Keep that in mind when you compare the numbers below.

Okay, enough science. How do the numbers compare?

Here are 20 websites. See how Site Strength compares with DataForSEO's backlink rank and Ahrefs DR.

DomainSite StrengthDataForSEO authorityDomain Rating by AhrefsAs of
wikipedia.org10096972026-09-23
github.com10098972026-09-23
nytimes.com9888942026-09-23
openai.com9390932026-09-23
stripe.com10091952026-09-23
shopify.com10096962026-09-23
example.com9390942026-09-23
loom.com8273912026-09-23
koronapos.com4944682026-09-23
fuel50.com4540592026-09-23
microsoft.com10095962026-09-23
cloudflare.com10089942026-09-23
adobe.com10095962026-09-23
anthropic.com8583922026-09-23
airtable.com8483912026-09-23
calendly.com9891952026-09-23
semrush.com8682922026-09-23
bubble.io7868862026-09-23
37signals.com7268842026-09-23
usefathom.com8373842026-09-23

The scores differ because each tool observes different links and calculates strength differently. Site Strength builds on the published PageRank and harmonic-centrality research described above.

Why use ours?

Big SEO tools already have authority scores. We built Site Strength for the moment you need that signal across a list of domains in your own tool or AI agent. You can call it directly, without a subscription or a bill for each lookup.

  • Fast: send a domain to the GET endpoint and get JSON back. In a live check of ten domains, every response arrived in under three seconds.
  • Free today: no account, no subscription, and no per-lookup charge. Get an API key from the site and start calling.
  • Made for your tools: use the HTTP endpoints or MCP to get Site Strength and Referring Domains into an SEO tool, script, or AI agent.

Try a domain in the API workspace, inspect the JSON, and copy the GET request into your code. For an agent, give it the setup guide or connect through MCP.

Where can you use it?

  • Your SEO agent: give it a list of competitors and ask which ones have the strongest links.
  • Your SEO tool: add a Site Strength column to a competitor report or domain list.
  • Your own research: check your site alongside competitors to see how the scores compare.

Sources & further reading