Google's search engine web crawlers are not what you think

Posted on
March 15, 2023
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The purpose of a (not-so-creepy) web crawler

Behind the scenes of SEO lies a crucial character: Spiderman!

No, just kidding.

It's actually web crawlers.

Web crawlers, also known as spiders or bots, are responsible for crawling the word wide web, indexing web pages, and gathering information for search engines, like Google and Bing. Crawlers serve as the foundation of search engines by systematically discovering and indexing web pages.

Crawlers analyze website content, extracting relevant information such as text, links, images and image alt tags, and metadata (think meta descriptions, meta titles, and even image title tags). This data is then used to build an index, which powers search engine result pages (SERPs).

Web crawlers revisit previously indexed pages to identify updates, new content, and changes. This process helps search engines maintain up-to-date search results.

Let's dissect the anatomy of a web crawler and explore its purpose, function, and significance in search engine optimization.

How Google's search engine crawlers work

Web crawlers follow a structured process to systematically explore and index web pages.

Here's a simplified breakdown of their functioning:

Seed URLs

Crawlers begin with a set of seed URLs, which can be popular websites, sitemaps, or user-generated queries. Seed URLs are the initial set of URLs that serve as the starting point for web crawlers. These URLs can be selected from various sources such as popular websites, sitemaps, or user-generated queries. They represent the entry points into the web that the crawler will begin exploring.

URL discovery

After obtaining the seed URLs, the crawler starts extracting links found on those pages. It parses the HTML code of each page and identifies the hyperlinks present within the content. These extracted links are then added to a queue for further exploration and retrieval.

Page retrieval

Once the crawler has a URL in its queue, it sends HTTP requests to the respective web servers hosting the web pages.

HTTP requests ask for the content of the URLs, and site servers respond by providing the HTML codes of your web pages. The crawler retrieves this content, which includes text (think meta descriptions, page titles, and header tags), images (think image alt text tags), scripts, and other resources associated with the page.

Parsing and extraction

After retrieving a web page, the crawler parses the HTML code to extract relevant information. It looks for specific elements such as headings, paragraphs, titles, metadata, and other structural components. The crawler extracts this content to be used for indexing and understanding the page's context.

Link extraction

During the parsing process, the crawler also identifies and extracts links present on the page. It looks for anchor tags (<a>) in the HTML code and collects the URLs they point to. These extracted links are added to the crawler's queue for future exploration, allowing the crawler to navigate and discover new pages.

Politeness and crawl rate

To ensure fair and responsible crawling, crawlers follow certain rules known as politeness guidelines. These guidelines prevent the crawler from overwhelming web servers and respect the preferences of website owners.

One common way to enforce politeness is by respecting the website's robots.txt file, which may contain directives specifying which parts of a site are allowed or disallowed for crawling. Additionally, crawl rate limits may be set to avoid excessive requests to a single server or domain, ensuring a balanced and controlled exploration of the web.

SEO implications of web crawlers

Understanding web crawlers is vital for effective SEO strategies. Consider the following:


Ensuring that your website is accessible and crawlable by search engine bots is fundamental. Properly structured HTML, well-labeled content, and optimized metadata enhance indexability.

Internal linking

Web crawlers rely on links to discover and navigate through web pages. Thoughtful internal linking structures, including sitemaps and logical navigation, help search engine bots crawl your site efficiently.

Crawl budget

Search engines allocate a "crawl budget" to each website, determining the frequency and depth of crawls. Optimizing your website's performance, reducing duplicate content, and prioritizing important pages can help maximize your overall crawling budget.

XML sitemaps

Providing XML sitemaps to search engines offers a structured map of your website, assisting crawlers in finding and indexing your pages more effectively.

Search engine crawler tips

To ensure that web crawlers can explore your website comprehensively and efficiently, consider the following best practices:


The robots.txt file is a text file - read by search crawlers - that is placed in the root directory of a website. It serves as a guide for Google's crawlers, instructing them on what should/should not be included in their scans.

Website managers can specify certain orders in the robots.txt file to control the behavior of search engine crawlers and prevent them from accessing sensitive or irrelevant information.


Website accessibility refers giving all users, and especially those with certain disabilities, the ability to easily consume your website content. In the context of search engine crawlers, accessibility plays a role in improving the performance and user experience of your website.

Fast loading times are crucial for search engine crawlers since they need to quickly retrieve and process site ages efficiently. By eliminating website pressures such as loading times, website owners can help to streamline the crawler's indexing and ranking process. This eventually makes it easier for crawler to better understand key information across your site.


Canonicalization is the process of specifying the preferred version of duplicate or similar content on a website. Duplicate content can occur when multiple URLs lead to the same or very similar content, which can confuse search engine crawlers. To address this, website owners can implement canonical tags in the HTML code of their pages.

These tags indicate the canonical or preferred version of the content, helping search engine crawlers understand which URL to consider for indexing and ranking purposes. Canonicalization helps consolidate the authority and relevance of the content and prevents potential issues related to duplicate content.

Mobile-friendly design

With the rise of mobile usage, search engines have shifted towards a mobile-first indexing approach. This means that the mobile version of a website is given priority in crawling and indexing, as it is considered the primary version for ranking purposes.

Having a responsive website design is crucial to ensure effective crawling and indexing by search engines. A good design layout enables the website to adapt and provide an optimal user experience across different devices and screen sizes. It includes elements such as responsive layouts, easily readable text, logical navigation, and optimized media files.

A mobile-friendly website increases its chances of being effectively crawled, indexed, and displayed in search engine results pages for mobile users.

Web crawlers are your best friend

Understanding the anatomy of a search crawler is crucial for anyone involved in SEO. By dissecting the components and functions of these web robots, we gain valuable insights into how search engines discover, analyze, and index web content. The crawler's ability to navigate through websites, follow links, and gather information plays a vital role in determining your search engine rankings.

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