a link gap is the set of domains that link to your competitors and not to you. that is the whole definition, and the reason it is worth a page is that the arithmetic behind it decides how useful the output is. a gap is a set difference over a link graph, so the answer changes with how many competitors you put in, which index you compute it over, and whether you count domains or pages. this post is the definition and the math. if you want to run one, the walkthrough is how to run a backlink gap analysis for free.
a link gap is the set difference between the domains linking to your competitors and the domains linking to you. every entry is a site that has already proven it will link to something in your category.
the set difference, worked out
two competitors, a handful of linking domains, and the whole computation written out. no scoring, no weighting, just sets:
you linked-by { alpha.com, beta.org }
competitor A linked-by { alpha.com, gamma.net, delta.io }
competitor B linked-by { gamma.net, delta.io, epsilon.co }
union of competitors' linkers
{ alpha.com, gamma.net, delta.io, epsilon.co }
minus your own linkers
{ alpha.com, gamma.net, delta.io, epsilon.co } - { alpha.com, beta.org }
link gap
gamma.net links to A and B <- 2 competitors, sort to top
delta.io links to A and B <- 2 competitors
epsilon.co links to B only <- 1 competitor
beta.org is yours alone and never appears: a gap is about
what you are MISSING, not what makes you different.the last line is the part people miss. a domain that links only to you never appears in a gap, because a gap describes what you are missing. that sounds obvious written down and it surprises people constantly, usually when a gap report comes back without their best link in it.
why a gap list beats a prospect list
the ordinary way to find link targets is to search for sites in your subject and pitch them. the problem is that you learn nothing about whether they link out at all. plenty of excellent sites simply do not.
a gap list inverts that. every entry is there because it already linked to a company like yours, so the question is no longer "does this site ever link out" but "why did they pick that company and not me". that is a far better question to open an email with, and it is the entire practical advantage of the technique.
how many competitors changes the answer
this is the setting that matters most and the one people leave on the default:
- one competitor gives a list padded with links nobody can replicate: their investors, their parent company, their founder's personal blog, the conference they sponsored.
- three or four competitors lets you count how many of them each domain links to. a domain linking to three rivals and none to you links to the category as a habit. those sort to the top and they are the ones worth writing to first.
- too many competitors and the intersection thins out until only the giant general-purpose sites survive, which are the least reachable entries on any list.
domains, not pages
a gap should be computed over referring domains rather than individual backlinks. one site linking to a competitor forty times is one relationship and one outreach email, not forty opportunities. counting pages inflates the list and buries the domains that matter under whichever site happens to have the most templated links. the distinction is worth being precise about, and referring domain vs backlink covers where the two counts come apart.
why two tools give different gaps
the set difference is not the variable. every tool computes it the same way, because there is only one way to compute it. what differs is the input: each tool runs the math over its own crawl, and no crawler sees the whole web. a domain missing from a tool's index cannot appear in that tool's gap, however real the link is.
the practical response is to treat the overlap between two tools as high confidence and the difference as coverage rather than error. for what sits behind each vendor's index, where ahrefs and moz get their backlink data goes through the crawlers one at a time.
our own gaps are computed over the open common crawl hyperlink graph, 121.1 million domains and 3.90 billion domain-level links in the current release. the advantage is not that it is bigger, because it is not always. it is that the input is public, so the gap is reproducible by anyone willing to process the dataset rather than being a number you have to take on trust.
what to do with the list
- sort by competitor count first, authority second. a domain linking to three rivals is a warmer target than a stronger domain linking to one.
- open the page that carries the link. a roundup, a comparison table and a passing mention need three different emails.
- drop what you cannot win. investor pages, parent companies, and anything paid. a gap list is a starting set, not a quota.
put your domain and up to three competitors into the free backlink gap analysis. the first 5 gaps come back for an email, sorted by how many of your competitors each domain links to, with no account to create.
faq
What is a link gap?
A link gap is the set of domains that link to your competitors but not to you. It is a set-difference over a link graph: take the domains linking to one or more competitors, subtract the domains already linking to you, and what remains is the gap. Each entry is a site that has already demonstrated it will link to something in your category, which is what separates a gap list from a generic prospect list.
What is the difference between a link gap and a backlink gap analysis?
The link gap is the result; the backlink gap analysis is the process that produces it. Analysts use the terms interchangeably in practice, along with link intersect and competitor link gap, and they all describe the same set-difference computation over the same kind of data.
How many competitors should I compare against?
Three to four is the practical sweet spot. One competitor produces a list padded with sites that link to that specific company for reasons you cannot replicate, such as being an investor or a parent company. Three or more lets you sort by how many competitors each domain links to, and a domain linking to three of your rivals and none to you is linking to the category as a habit rather than doing anyone a favour.
Why do link gap tools disagree with each other?
Because each one computes the same set difference over a different index. No crawler sees the whole web, so the inputs differ before any math happens. Treat the overlap between two tools as high confidence and the difference as each tool's crawl coverage rather than as one of them being wrong.
Is a link gap analysis free anywhere?
CrawlGraph returns your first 5 gaps for an email with no account to create, and the full ranked list is included in a paid plan. It runs on Common Crawl's open hyperlink graph, which is public data, so the analysis is reproducible from the raw dataset by anyone willing to process it themselves.
writes the queries we run internally. ships one tactical post a week.
plus one when a new common crawl release lands. that is all.