We're building Rankfield to give AI agents all the data they need to do SEO. Site Strength and Referring Domains are available today. The rest is in the works.
Site Strength is our 0–100 score for a website's link strength. If you've used Ahrefs' Domain Rating, Semrush's Authority Score, or Moz's Domain Authority, you'll recognize the idea: a score that helps you compare websites. Our version focuses on the links pointing to a domain and the websites behind those links.
Referring Domains tells you how many different websites link to a domain. Fifty links from one website count as one referring domain. Fifty websites linking once each count as fifty.
Our main focus is making this data easy for agents to get and use. You can get an API key without creating an account, call two simple GET endpoints, or connect through MCP. Both metrics are free to use today, with no per-lookup charge. We think setting up a data source should take less effort than writing the prompt that uses it.
But where does the data come from?
For these first two metrics, we use Common Crawl's published web data. It records links between websites. We count the distinct websites linking to a domain for Referring Domains, then use that count and the wider pattern of links to calculate Site Strength.
The math draws on PageRank (Brin and Page, 1998) and harmonic centrality (Boldi and Vigna, 2014). PageRank considers where links come from and passes weight through them. Harmonic centrality measures how easily other websites can reach a domain through chains of links. Together, they help us look beyond a raw link count.
We've written longer explanations of how Site Strength works and what goes into Referring Domains. Those cover the methods and what each result includes.
How does Site Strength compare?
Here are five domains with Site Strength, DataForSEO authority, and Ahrefs Domain Rating side by side.
| Domain | Site Strength | DataForSEO authority | Domain Rating by Ahrefs | As of |
|---|---|---|---|---|
| github.com | 100 | 98 | 97 | 2026-09-23 |
| openai.com | 93 | 90 | 93 | 2026-09-23 |
| loom.com | 82 | 73 | 91 | 2026-09-23 |
| 37signals.com | 72 | 68 | 84 | 2026-09-23 |
| fuel50.com | 45 | 40 | 59 | 2026-09-23 |
The numbers differ because each tool uses its own data and methodology. Our method builds on the published research above. You can see all 20 examples in the Site Strength article.
Why should I use Rankfield?
Because getting SEO data into an agent should be easy and affordable. A competitor report can involve dozens of lookups. We want you to be able to run them, change your prompt, and try again without paying for every request.
That is why we offer accountless keys, free access to both metrics, and JSON responses your agent can use directly. HTTP works for agents that can call APIs; MCP gives compatible assistants a ready-made connection.
Try it yourself. Enter your website below, get a key, and copy the prompt into Claude, ChatGPT, or your SEO agent. It asks for both metrics and the referring websites in one report.
Your first SEO lookup
Pick a domain. Your API key is included when you copy.
Check openai.com with Rankfield. Report Site Strength, Referring Domains, and the linking websites returned by the API.
No account needed. Get your key, then copy the prompt.
This preview connects to localhost. For Claude or ChatGPT in the cloud, use the live prompt widget.
Your agent needs HTTP access or a connected MCP tool to run the lookup. If you need to connect it first, follow the agent setup instructions.
Will you offer more SEO data?
Yes. Site Strength and Referring Domains are the starting point. We're working on keyword trends, including week-over-week (WoW), month-over-month (MoM), and year-over-year (YoY) changes.
That will let your agent look at whether interest in a keyword is growing, falling, or following a seasonal pattern. These metrics are in development; we'll share them here as they become available.
The goal stays the same: more SEO work your agent can do with a simple request. Start with your first lookup.