Internal Links

What are Internal Links?

Internal links are hyperlinks that point at (target) the same domain as the domain that the link exists on (source). In layman's terms, an internal link is one that points to another page on the same website.

Code Sample

<a href="http://www.same-domain.com/" title="Keyword Text">Keyword Text</a>

Optimal Format

Use descriptive keywords in anchor text that give a sense of the topic or keywords the source page is trying to target.

Why are Internal Links Important?

Internal links are useful for three main reasons:

• They allow users to navigate a website.
• They help establish information hierarchy for the given website.
• They help spread link equity (ranking power) around websites.

What is an Internal Link? And how is it different to an External Link?

Internal links are links that go from one page on a domain to a different page on the same domain. They may be used in the main navigation menu or on the content of the page. Alternatively external links point to another domain, this includes links from a page on your site to another site, and links pointing from other sites to your site, also called backlinks.

SEO Best Practice

Internal links are most useful for establishing site architecture and spreading link equity (URLs are also essential). For this reason, this section is about building an SEO-friendly site architecture with internal links.

On an individual page, search engines need to see content in order to list pages in their massive keyword–based indices. They also need to have access to a crawlable link structure—a structure that lets spiders browse the pathways of a website—in order to find all of the pages on a website. Hundreds of thousands of sites make the critical mistake of hiding or burying their main link navigation in ways that search engines cannot access. This hinders their ability to get pages listed in the search engines' indices. 

In the example below, Google's spider has reached page "A" without internal links it won't be able to locate the other pages.
Great content, good keyword targeting, and smart marketing don't make any difference at all if the spiders can't reach those pages in the first place. The same problem will be faced by human visitors.

Structural Internal Links & Site Architecture 

The optimal structure for setting up your website's structure internal links would look similar to a pyramid (where the page on the top is homepage):

This structure has the minimum amount of links possible between the homepage and any given page. Crawl depth is a number indicates a pages distance from the home page. A higher crawl depth could affect a pages crawlability. Important, revenue driving pages should have a lower drawl depth while maintaining a clear and organized site architecture. This is helpful because it allows link equity (ranking power) to flow throughout the entire site, thus increasing the ranking potential for each page. This structure is common on many high-performing websites in the form of category and subcategory systems.

You can use Moz Pro Site Crawl to identify crawl depth for pages on your site.

Structural Links & Contextual Links

No matter how well you plan your site architecture no website maintains a perfect cascading chandelier-like structure. Internal links can be both structural and contextual, and these two types of links work together to allow users to navigate a website and help spread link equity.

Implementing Internal Links on Your Site

Internally linking to a URL located at http://www.example.com/mammals... with the anchor text "cats" is a good example of a contextual internal link. Below is the format for a correctly formatted internal link. Imagine this link is on the domain jonwye.com.

In the above illustration, the "a" tag indicates the start of a link. Link tags can contain images, text, or other objects, all of which provide a "clickable" area on the page that users can engage to move to another page. This is the original concept of the Internet: "hyperlinks." The link referral location tells the browser—and the search engines—where the link points. In this example, the URL http://www.jonwye.com is referenced. Next, the visible portion of the link for visitors, called "anchor text" in the SEO world, describes the page the link is pointing at. In this example, the page pointed to is about custom belts made by a man named Jon Wye, so the link uses the anchor text "Jon Wye's Custom Designed Belts." The </a> tag closes the link, so that elements later on in the page will not have the link attribute applied to them.

This is the most basic format of a link—and it is eminently understandable to the search engines. The search engine spiders know that they should add this link to the engine's link graph of the web, use it to calculate query-independent variables, and follow it to index the contents of the referenced page.

Below are some common reasons why pages might not be reachable, and thus, may not be indexed.

Links in Submission-Required Forms

Forms can include elements as basic as a drop–down menu or elements as complex as a full–blown survey. In either case, search spiders will not attempt to "submit" forms and thus, any content or links that would be accessible via a form are invisible to the engines.

Links Only Accessible Through Internal Search Boxes

Spiders will not attempt to perform searches to find content, and thus, it's estimated that millions of pages are hidden behind completely inaccessible internal search box walls.

Links in Un-Parseable Javascript

Links built using Javascript may either be uncrawlable or devalued in weight depending on their implementation. For this reason, it is recommended that standard HTML links should be used instead of Javascript based links on any page where search engine referred traffic is important.

Links in Flash, Java, or Other Plug-Ins

Any links embedded inside Flash, Java applets, and other plug-ins are usually inaccessible to search engines.

Links Pointing to Pages Blocked by the Meta Robots Tag or Robots.txt

The Meta Robots tag and the robots.txt file both allow a site owner to restrict spider access to a page.

Links on pages with Hundreds or Thousands of Links

The search engines all have a rough crawl limit of 150 links per page before they may stop spidering additional pages linked to from the original page. This limit is somewhat flexible, and particularly important pages may have upwards of 200 or even 250 links followed, but in general practice, it's wise to limit the number of links on any given page to 150 or risk losing the ability to have additional pages crawled.

Links in Frames or I-Frames

Technically, links in both frames and I-Frames are crawlable, but both present structural issues for the engines in terms of organization and following. Only advanced users with a good technical understanding of how search engines index and follow links in frames should use these elements in combination with internal linking.

By avoiding these pitfalls, a webmaster can have clean, spiderable HTML links that will allow the spiders easy access to their content pages. Links can have additional attributes applied to them, but the engines ignore nearly all of these, with the important exception of the rel="nofollow" tag.

Want to get a quick glimpse into your site's indexation? Use a tool like Moz Pro, Link Explorer, or Screaming Frog to run a site crawl. Then, compare the number of pages the crawl turned up to the number of pages listed when you run a site:search on Google.

Rel="nofollow" can be used with the following syntax:

<pre><a href="/" rel="nofollow">nofollow this link</a></pre>

In this example, by adding the rel="nofollow" attribute to the link tag, the webmaster is telling the search engines that they do not want this link to be interpreted as a normal, juice passing, "editorial vote." Nofollow came about as a method to help stop automated blog comment, guestbook, and link injection spam, but has morphed over time into a way of telling the engines to discount any link value that would ordinarily be passed. Links tagged with nofollow are interpreted slightly differently by each of the engines.

Frequently Asked Questions

What is internal linking vs external linking?

Very simply, internal linking occurs when a site links to other URLs on the same site, whereas external linking occurs when a site links to URLs on a different site. Put another way, internal links are when you link to your own pages, while external links point to pages on other domains.

Why are internal links important?

Internal links are important because they can help Google understand and rank your website better. By giving Google links to follow along with descriptive anchor text, you can indicate to Google which pages of your site are important, as well as what they are about. Internal links are also good for user experience and may improve engagement.

How many internal links are too many?

While there is no definite answer as to how many internal links on a page are too many, Google has indicated they can crawl 100s of links per page. Practically speaking, lots of links isn't always good for user experience, and limiting the number of links per page to a reasonable number (typically around 100 or less) can provide additional SEO benefits.

How do you find internal linking opportunities?

One of the best ways to find internal linking opportunities is to find pages on your site that rank for related topics and make sure they link with descriptive anchor text. 

Keep learning

• The Beginner's Guide to Link Building - Everything you need to get started on one of the most important things you can do for your SEO.
• The Professional's Guide to Link Building & Link Earning Tactics - Paddy Moogan shares his vast wealth of knowledge on advanced link building and link earning tactics used by professional SEOs.
• External Links
• Anchor Text
• Link Equity
• Webmaster Guidelines - Google's Official Guidelines for Webmasters.
• Text Links and PageRank - Former Head of the Webspam Team at Google, Matt Cutts', thoughts on hyperlinks in relation to SEO and Google.

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