SEOtoolsAPI metrics
How Gravity Score works
Gravity Score measures a host’s link-based authority using its connections to a trusted reference network and the support it receives from other hosts. The result is an integer from 0 to 100, available as gravity_score in the Domain Data API.
This page explains the model’s principles and how to interpret its output. Trust-source identities, exact weights, thresholds and computation parameters remain private to limit manipulation.
A score for a host
The scoring model represents the web as a directed graph. A node represents a host, and a link relationship points from a linking host to a linked host. Direction matters: receiving a link and linking out are different relationships.
Gravity Score describes the normalized requested hostname. It does not automatically combine every subdomain into a single company-wide score. For example, example.com and news.example.com can have different scores because their observed link relationships differ. The API applies its documented hostname normalization before looking up the score.
This scope differs from domain age, which uses the registrable domain, and from homepage Page Authority, which describes a particular page. Read the input and normalization rules when comparing results across hosts.
From page links to host relationships
The model uses observed external link relationships. Page-level links are considered in the context of their source and target hosts, so many links between the same two hosts do not represent the same breadth of support as links from many different hosts. A large number of repeated links does not produce a proportional increase in authority.
Link attributes affect whether an ordinary graph relationship can carry authority. Links marked nofollow, ugc or sponsored are not treated as ordinary followed recommendations. A relationship can contain a mixture of link types; the existence of a backlink alone does not establish that it contributes to Gravity Score.
Trusted reference evidence provides an additional basis for evaluating authority. It is assessed under the model’s source policies rather than inferred from the total number of backlinks. The reference set and its selection rules are not published.
Trust, distance and supporting hosts
Authority is anchored in trusted reference evidence and can propagate through eligible host relationships. Connections nearer that evidence carry more significance than increasingly remote connections. This makes the structure of the link network relevant, alongside the number of links it contains.
Support from qualifying referring hosts also affects the result. Additional support has diminishing returns, so increasing the amount of similar evidence produces progressively smaller gains. Link volume cannot be interpreted as a fixed number of score points.
These effects work together. A host with fewer but stronger connections can score above a host with a much larger backlink total. Two hosts with similar totals can differ because their referrers occupy different positions in the observed network or because different relationships qualify to carry authority.
The model produces a bounded value that is rounded to an integer. Rounding reduces the distinction between nearby results, especially at the lower end of the scale. Equal scores do not imply identical link profiles.
Limiting authority from spam signals
Spam signals can prevent a linking host from passing authority through its outgoing relationships. A host can therefore have visible backlinks without all of those referrers contributing to its Gravity Score.
Being limited as a source of authority is separate from receiving a score. A host can still have a Gravity Score based on its incoming evidence even when its own outgoing links do not pass authority. Gravity Score and Spam Score answer different questions and are returned as separate fields.
These controls reduce the influence of some low-quality link patterns, but a score does not certify that a site is safe, accurate or free of spam. It is a link-based metric, not a security assessment or a review of the site’s content.
What the number means
A higher value indicates stronger authority under the Gravity model. The scale is not a probability, a percentage of trustworthy pages, a percentile or a prediction of a search-engine ranking. A score of 40 does not mean twice the authority of a score of 20.
| Value | Interpretation |
|---|---|
| 1 to 100 | A positive stored result on the Gravity scale. Interpret it alongside the host’s link profile and the available data. |
| 0 | A stored zero. This can reflect insufficient qualifying connections, a result rounded to zero or a host that has not yet been processed. The value alone does not distinguish these cases. |
null | No usable stored score is available to the API. This is different from a known zero. |
There are no universal score bands that establish whether a host is good or bad. Compare hosts with a similar purpose and scope, retain the observation date, and review the underlying link evidence before making a decision. Small changes can reflect rounding or updates elsewhere in the network.
Coverage and background updates
Gravity Score depends on the relationships present in the available data. Unobserved links cannot contribute. Missing crawl coverage, recently added or removed links, and differences between hosts can affect the result. A low score does not prove that a host has no valuable links elsewhere on the web.
Scores are computed in background cycles and saved for retrieval. An API request reads the stored result; it does not rebuild the authority graph or recalculate Gravity Score on demand. Newly observed evidence may take a later computation cycle to affect a score.
The host’s own backlinks do not need to change for its score to change. Updates to referring hosts, their qualifying relationships or the model’s reference evidence can affect the authority that reaches it. During a background update, different hosts can reflect different stages of the refresh.
Backlink summary counts and individual backlink listings describe related data with their own scopes and update behavior. They are not a complete export of the scoring model’s inputs. Their totals should not be used to reconstruct a Gravity Score or assume that every listed link contributes authority.
Using Gravity Score through the API
Request GET /api/v1/domain-data?domain=example.com with your API key. The response includes gravity_score alongside Domain Authority, homepage Page Authority, Spam Score, domain age and backlink counts. The scale field is 100 for all four scores.
Preserve null as unavailable and 0 as zero in your application. Do not replace missing scores with zero, infer a processing status from a zero, or treat the score as a count of backlinks. The same numeric scale does not make the four metrics interchangeable.
See the Domain Data reference for authentication, hostname normalization, response fields and request accounting. You can also try Domain Data in the public demo.