What is internal linking in SEO?

In an online store, internal linking is everything that takes you from one page to another without leaving the site: the menu, the category page that links to each product, the breadcrumbs, the related products and the links inside a description or a guide. For the shopper it is how they get around. For a search engine it is something more: the map it uses to discover your pages and decide which ones weigh more. A product page that no link leads to exists for whoever has the URL, and for almost nobody else.

How it works

Google knows some pages because it has already visited them. The rest it discovers when it extracts a link from a known page to a new one, or when you send it a list of URLs in an XML sitemap.⁠^{[1]Google Search Central. In-depth guide to how Google Search works} Beyond discovery, links also serve as a signal for judging how relevant pages are.⁠^{[2]Google Search Central. SEO link best practices for Google}

For a store, Google spells out three things.⁠^{[3]Google Search Central. Help Google understand your ecommerce site structure}

• Importance is distributed through links. The more links a page receives within a site, the more relative importance it has compared with the others. That is why it recommends linking a best-selling product from the homepage or from other content, such as articles or newsletters.
• The hierarchy runs from the menu to the product page: links from the menu to categories, from categories to subcategories and from subcategories to all the product pages. If a category does not link directly to all its products, Googlebot may not find all of them by crawling alone. When you cannot link everything, the alternative is a sitemap or a Google Merchant Center feed.
• URL structure does not count as hierarchy. Google, in general, does not look at the folders in a URL to understand a site's structure: it analyzes the links between pages.

Its minimum rule is simple: every page you care about has to receive at least one link from another page on your site. There is no ideal number of links per page, and Google adds that if they seem like too many to you, they probably are.⁠^{[2]Google Search Central. SEO link best practices for Google}

What counts as a link

Google only reliably follows <a> elements with an href attribute. These are links it can follow and links it cannot:⁠^{[2]Google Search Central. SEO link best practices for Google}

<!-- Yes -->
<a href="https://store.example/backpacks">Backpacks</a>
<a href="/backpacks/camera">Camera backpacks</a>

<!-- No -->
<a routerLink="backpacks/camera">Camera backpacks</a>
<span href="/backpacks/camera">Camera backpacks</span>
<a onclick="go('/backpacks/camera')">Camera backpacks</a>

A link that JavaScript inserts counts if it ends up as a normal <a href>: Googlebot renders the page and looks for links again in the resulting HTML.⁠^{[4]Google Search Central. Understand JavaScript SEO basics} But Google also reminds you that not all bots can run JavaScript,⁠^{[4]Google Search Central. Understand JavaScript SEO basics} and for those, a link that is not in the source HTML does not exist.

The link text

A link's visible text tells people and Google something about the page it points to. Google wants it descriptive, reasonably short and related to the destination, with no generic phrases like "click here" or "read more," and it suggests a test: read only the link text, out of context, and see whether it makes sense. On a linked image, the link text is its alt attribute, the alt text. And it warns against the opposite excess: stuffing links with keywords is padding.⁠^{[2]Google Search Central. SEO link best practices for Google}

In a store

A fictional example: the links that lead to a camera backpack's product page on a Shopify store, and who can follow each one.

The fourth row is the one that surprises. In Shopify themes, the related products block is not filled in when the page is generated: the theme has to request it with JavaScript from the recommendations API, and Shopify recommends planning for an empty state or not showing the section, because recommendations load asynchronously.⁠^{[5]Shopify Dev Docs. Show related products on product pages} Those links help the shopper, and Google can see them when it renders, but a product reachable only from that block is not well linked: what holds it up is the category.

How to check it

1. Get from the homepage to a product page using only links, without the internal search, and count the clicks. If there is no path, Google depends on the sitemap to find it.⁠^{[3]Google Search Central. Help Google understand your ecommerce site structure}
2. Repeat the route with JavaScript turned off (in Chrome, from the developer tools). What you cannot navigate that way, a bot that does not run JavaScript cannot either.⁠^{[4]Google Search Central. Understand JavaScript SEO basics}
3. Open the source code (Ctrl+U) of a category and search for a product's name: it has to be inside an <a href>.⁠^{[2]Google Search Central. SEO link best practices for Google}
4. Read only the link texts on a product page and a category. If any does not say where it goes, rewrite it.⁠^{[2]Google Search Central. SEO link best practices for Google}
5. Cross your sitemap with the linked pages. A desktop crawler gives you the list of URLs it reaches by following links; the sitemap's product pages that do not show up in it receive no internal link.

Related concept: XML sitemap

The sitemap and internal linking serve the same purpose at first, getting the search engine to discover your URLs, which is why they get confused. The sitemap is a list; internal linking is a structure. The sitemap gives Google the addresses, but does not tell it which ones matter most or what each is about. Links do: the number of links a page receives gives it its weight within the site, and each link's text describes the destination.⁠^{[3]Google Search Central. Help Google understand your ecommerce site structure}⁠^{[2]Google Search Central. SEO link best practices for Google} Google treats the sitemap as the alternative for what you cannot link, not as a substitute for links.⁠^{[3]Google Search Central. Help Google understand your ecommerce site structure}

To go further, the reading path for this topic orders the rest of the terms, up to indexing, and the guide to what an AI crawler sees in your store checks it page by page.