How to Run a Backlink Gap Analysis in Semrush

Disclaimer: This post contains affiliate links in which I receive commissions. The opinions are my own.

Every site that links to two of your competitors and not to you has already shown it will link to a page like yours. That makes it the warmest cold-outreach list you can build, and a backlink gap analysis builds it in about twenty minutes.

I run this on my own site and recommend it to agencies because it replaces the worst part of link building, which is guessing who to email. Here’s the exact process in Semrush.

Table of contents

Open Table of contents

• Step 1: Pick the right competitors
• Step 2: Run the Backlink Gap tool
• Step 3: Cut the list down to what’s winnable
• Step 4: Check that your page deserves the link
• Step 5: Write the outreach
  • A prompt to speed up the sorting
• Step 6: Track what happened
• FAQ
  • How many competitors should I compare against?
  • Is a domain that links to only one competitor worth emailing?
  • Does a gap analysis work for a brand-new site?
  • How long until I see results?

Step 1: Pick the right competitors

The list is only as good as the sites you compare against. Use search competitors, not the brands you admire. A search competitor is whatever ranks on page one for the keywords you want to rank for.

1. Take your five most important target keywords.
2. Search each one and note the domains that show up repeatedly.
3. Drop giants that can’t be compared with you (Wikipedia, Forbes, big marketplaces). Their links come from a brand you don’t have.
4. Keep three or four domains of roughly your size or a little bigger.

If you already did the competitor mapping from my Semrush competitor research guide, reuse that list.

Step 2: Run the Backlink Gap tool

In Semrush, open the Backlink Gap tool under the Link Building toolkit. Enter your domain in the first field and your competitors in the rest, then run the comparison.

Semrush returns every referring domain that links to at least one of the competitors, with a count of how many of the sites each domain links to. Then sort and filter:

• Sort by the number of competitors linked. A domain that links to three of your four rivals is a far better prospect than one that linked to a single rival once.
• Filter for domains that don’t link to you. This is the gap itself.
• Sort by Authority Score as a tiebreaker, not as the main sort. A relevant site with a modest score beats an irrelevant one with a high score.

Export the result to a spreadsheet. A typical run gives you a few thousand rows. You will use maybe 50 of them.

Step 3: Cut the list down to what’s winnable

Most of that export is noise. Delete these on sight:

1. Directories and link farms. Anything where the “link” is a paid listing.
2. Forum and comment profiles. Easy to get, worthless, and sometimes a penalty risk.
3. Press releases and syndicated copies. The competitor didn’t earn that link, and you can’t either.
4. Sites with no recent content. If the last post is from 2021, nobody is reading your email.

What remains falls into four buckets. I sort them in this order because the first bucket converts best:

Bucket	What it looks like	What to pitch
Resource pages	“Best tools for X” lists that link to rivals	Your page, with one sentence on what it adds
Roundups and reviews	A blogger who reviewed two competitors	A comparison or review request
Guest-post sites	Competitor bylines on the same blog	A specific post idea
Broken or dead links	Pages linking to a competitor URL that now 404s	Your page as the replacement

For the last bucket, my broken-link guide shows how to check a URL before you pitch.

Step 4: Check that your page deserves the link

The gap tells you who links to your rivals. It doesn’t tell you why. Open three or four of the linking pages and look at what the link points to. Usually it’s one of three things: a tool, a data study, or a clear step-by-step guide.

If you have nothing comparable, the right move is to build that asset first and then pitch. Emailing a resource-page owner with a thinner page than the one they already link to gets ignored every time. I’d rather send 20 pitches for a page I’m proud of than 200 for one I’m not.

Step 5: Write the outreach

Keep every email to four sentences:

1. Say which page of theirs you’re writing about, by name.
2. Say what your page covers that the page they already link to doesn’t.
3. Give the URL.
4. Stop. No flattery paragraph, no “hope you’re well.”

Send from a real address on your own domain. Follow up once, five to seven days later, and then let it go. The reply rate on cold link requests is low, usually in the single digits, which is exactly why you start with a list of 50 and not 10.

A prompt to speed up the sorting

If you don’t want to read 50 pages, paste your shortlist into Claude or ChatGPT:

Here is a list of URLs that link to my competitors but not to me, plus a one-line description of my page. For each URL, tell me which of these buckets it fits: resource page, roundup or review, guest post, broken link, or skip. Then write a four-sentence outreach email for each one that isn’t skip. Do not invent facts about the site; if you can’t tell what a page is about from the URL, mark it “check manually.”

Read the “check manually” rows yourself, and open a sample of the others. These models will confidently describe pages they haven’t seen.

Step 6: Track what happened

Log each pitch in the same spreadsheet: date sent, reply, link won or not. After two or three rounds you’ll see which bucket works for your niche, and you can drop the rest. Re-run the Backlink Gap tool every quarter, because competitors keep earning new links and the list refreshes itself.

Semrush is the tool I use here. If you’re deciding between it and Ahrefs, I compared them in Ahrefs vs Semrush, and my Semrush review covers what the plans include. Either one can do a gap analysis; the process above doesn’t change.

FAQ

How many competitors should I compare against?

Three or four. Fewer gives you a thin list, and more gives you thousands of rows where each domain links to only one rival, which is the weakest signal in the data.

Is a domain that links to only one competitor worth emailing?

Occasionally, if it’s highly relevant, such as a niche blog in your exact topic. As a rule, start with domains that link to two or more.

Does a gap analysis work for a brand-new site?

It works, but you’ll win fewer links until you have pages worth linking to. Build one strong resource first, then run the analysis.

How long until I see results?

Links from outreach arrive over weeks, and ranking movement lags behind that. I’d judge the first round by links won, not rankings.

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This guide is part of alejandrorioja.com — written by Alejandro Rioja, who now builds AI agent systems for founders.