What Is a Backlink? Complete SEO Guide

What is a backlink

A backlink is a hyperlink on one website that points to a page on another domain. From the receiving site’s perspective it is an inbound link; from the source site’s perspective it is an outbound link. In SEO terms a backlink functions as an external reference that signals to search engines and users that the source site found the target content worth mentioning or citing.

Backlinks differ from internal links: an internal link connects pages within the same domain and helps distribute relevance and site structure, while a backlink is an off‑page signal used to evaluate a page’s authority, relevance and editorial acceptance outside its own site.

How backlinks work: crawling, indexing and ranking

Backlinks interact with three separate stages of search: crawling (discovery and fetching), indexing (what gets stored in the index) and ranking (how results are ordered). These stages are distinct: a link can help a crawler discover a URL, but discovery alone does not guarantee the page will be indexed or that the link will influence ranking.

Practical implications: search engines use signals embedded in backlinks—such as source relevance, anchor text, link placement and the source page’s indexability—alongside on‑page content and user‑experience signals to decide how to surface results. Note that Google uses the mobile version as its primary basis for crawling and indexing; since July 2024 Google crawls sites for Search with Googlebot Smartphone by default.

Also keep in mind two modern search realities: Google removed traditional cached pages in early 2024, and AI-driven features such as Search Generative Experience or AI overviews are now mainstream in many SERPs. Those features may use signals from links as part of the broader relevance and knowledge synthesis process.

Link attributes and HTML examples

There is no rel="dofollow" attribute. In SEO jargon a "dofollow" link simply means a normal link without rel=nofollow, rel=sponsored or rel=ugc. Use rel attributes to clarify link intent to search engines and site visitors:

A standard editorial link without a special rel value: example.

For paid placements, use rel="sponsored": example.

For user‑generated content, use rel="ugc": example.

For links you do not want to suggest for ranking, use rel="nofollow" as a hint. Since 2019 Google treats rel="nofollow" as a hint rather than a strict directive; the exact treatment per link is not public.

How to verify and audit backlinks from outside a publisher

You typically do not have Search Console access for third‑party sites, so use checks that work externally. The checklist below helps you confirm a backlink exists, assess its quality, and detect common problems.

Checklist (external verification)

1. Fetch the page headers to confirm the page responds and to inspect server headers (robots policies, redirects): use curl -I https://publisher.example/path. Look for HTTP status, X‑Robots‑Tag headers and redirects.

2. Fetch the HTML the server returns to a specific user agent to see the raw markup (no -I): curl -A "YourUserAgentString" -L https://publisher.example/path. Verify the link is present in the HTML source (not only injected later by JavaScript).

3. Check the rendered DOM in a browser. Open Chrome DevTools → Elements to confirm the anchor is visible to users, and use the Network tab to watch for late JavaScript insertion or lazy loading that may affect how search engines see the link.

4. Confirm the link’s attributes and placement. Is the anchor in the main content or buried in a footer, widget, or author box? Does the anchor text look natural? Does the anchor include rel attributes such as rel="sponsored" or rel="nofollow"?

5. Inspect indexation signals. From outside, the site: operator can be a quick indicator (for example, site:publisher.example "unique phrase"), but it is not definitive. A page might be known to Google yet not appear in a site: query, and the reverse can also occur. For pages you own, use the Google Search Console URL Inspection tool for authoritative indexation data; for external pages rely on public signals plus your judgment.

6. Check for blocking meta tags in the HTML (open the source and find <meta name="robots" ...>) and server headers (X‑Robots‑Tag). A page blocked from indexing is usually far less valuable as an SEO reference.

7. Measure referral traffic if you can: ask the publisher to provide a sample of analytics data or use UTM-tagged links. Referral traffic and engaged visitors are often the most practical indicators a placement has value beyond a raw link.

Common mistakes and how to avoid them

Buying links based only on third‑party scores (DR/DA/TF) without verifying editorial context, indexability and placement. Those metrics are proxies from third‑party tools and are not Google properties or direct ranking signals.

Accepting links that are inserted via client‑side JavaScript in ways that search engines don’t reliably process, or placing links in low‑visibility locations like hidden widgets. Always confirm the link exists in the HTML served to crawlers and is visible in the rendered DOM.

Failing to use appropriate rel attributes for paid placements. Google’s guidance is clear: paid or sponsored links should use rel="sponsored" or rel="nofollow"; rel="ugc" is for user‑generated links. Mislabelled paid links risk being treated as link spam.

When a backlink is genuinely useful

A backlink tends to be most useful when several of these conditions are true: the source site is topically relevant, the link appears within editorial content (not purely a list of paid links), the source page is indexable, the anchor text is natural and helpful, and the placement drives at least some referral traffic or visibility to real users.

Marketplaces and publisher networks can speed discovery of potential placements. Use them as a starting point, but apply the verification checklist above: confirm indexability, editorial context, link attributes and audience fit before relying on a purchase or outreach decision. For example, a marketplace that exposes indexation or editorial placement data lets you make evidence‑based choices; still perform your own checks.

Google linkspam policy and paid links

Google’s guidance is that links primarily intended to manipulate search rankings can be treated as link spam. Paid links should be disclosed with rel="sponsored" or rel="nofollow"; failing to use appropriate rel attributes increases the risk that Google will ignore the links, apply algorithmic adjustments, or in rare cases surface a manual action if webspam reviewers find deliberate manipulation. Distinguish between manual actions (rare, visible in Search Console for sites you own) and automatic algorithmic adjustments (common and not visible).

Troubleshooting: typical scenarios and steps

Scenario: a publisher reports they added a link but you see no referral traffic and no ranking effect. Steps: confirm the link exists in the HTML (curl without -I), confirm the page is indexable (site: checks plus look for noindex/X‑Robots‑Tag), confirm the link placement is editorial, and ask the publisher to provide a screenshot or the page URL so you can verify anchor text and rel attributes. Finally, ask whether the link was added via a widget or through the CMS in a way that might render differently to crawlers.

Scenario: a paid placement was mislabelled (no rel="sponsored"). Request a correction to include rel="sponsored" or rel="nofollow". Keep a record of communications and consider whether the editorial context still justifies the placement if the publisher cannot or will not add the rel attribute.

If you use marketplaces: treat listings as introductions, not guarantees. Verify indexability, placement and rel attributes before completing any transaction.

Further reading: Read the Technical SEO Guide — or Browse publishers for backlinks.

FAQ

Do nofollow links help SEO?

rel="nofollow" is treated by Google as a hint since 2019. That means such links may or may not be used by Google for crawling, indexing signals or ranking—Google’s exact treatment per link is not public. Nofollow links can still drive referral traffic and brand exposure, which are valuable even if the link’s ranking effect is uncertain.

How can I check whether a publisher page is indexed?

From outside the domain, use the site: operator with a unique phrase as an indication, but treat it as non‑definitive. For pages you own, use the Google Search Console URL Inspection tool for authoritative indexation status. Also inspect the page for noindex meta tags or X‑Robots‑Tag headers using curl -I and view the HTML source for <meta name="robots"> tags.

Are paid backlinks allowed in SEO?

Paid links are permitted only if they are disclosed correctly. Google’s guidance requires that paid or sponsored links use rel="sponsored" or rel="nofollow" to indicate the commercial nature of the placement. Links whose primary purpose is to manipulate rankings can be treated as link spam; the consequences include Google ignoring the links or applying algorithmic adjustments, and in some cases manual action.

Which backlink metrics should I trust?

Third‑party metrics such as Domain Authority or Domain Rating are useful proxies for initial filtering, but they are not Google metrics and do not directly determine ranking. Use them alongside direct checks—indexability, editorial placement, anchor text, referral traffic and audience relevance—to form a practical view of a link’s potential value.