A crawler, also known as a web crawler or spider, is an automated bot that systematically browses the internet to discover and index websites.
Think of a crawler like a digital librarian. It browses websites and collects information about their content, structure, and links.
The information is then stored in a massive database called an index.
This information can be used later depending on the purpose of the company that operates the crawler.
The most advanced crawler is Googlebot, which collects data and information for the Google search engine.
It helps Google understand and organise all the information on the internet so Google can show relevant results for users’ searches in the SERPs.
But search engines are not the only companies that use crawlers.
There are a number of good (and bad) crawlers that serve different functions online. The crawlability of your site also affects how often a crawler will visit your site.
What Will I Learn?
Search indexing is simply the process of organising and storing information collected by a web crawler.
Think of an index like a huge digital warehouse. It serves as a place to store the information. Whenever a search engine needs the information and data in the index, it goes in and gets it.
Here’s how the whole process works:
The reason this works so well is because it makes information collected by crawlers accessible in seconds.
When you search for something online, Google doesn’t need to scan the entire internet to provide you with relevant results.
It simply pulls the information from the index.
Cool, right?
Web crawlers are important because they help search engines discover quality content and display it in the organic search results.
This allows users to easily access information in just a few clicks!
But that’s not all…
Building an index of websites and content is only half the job.
Web crawlers continue to crawl websites they find to ensure that the search results stay relevant and up-to-date.
They also help to identify broken links and other technical issues on websites.
That’s why Google Search Console is such a great tool. It essentially shows you what your website looks like through the eyes of Google.
The bottom line is this:
Without web crawlers, search engines couldn’t provide accurate results for every search you make. They’re the backbone of quality information at your fingertips.
Web crawlers work by following a systematic process. They start with a list of URLs (called seed URLs) to visit.
From there, they visit each URL and read the content on the page. The crawlers then identify outbound links to other websites within the seed URLs.
This allows them to follow these links and discover new URLs to visit. The process is then rinsed and repeated.
Simple, right?
Internal links also play a significant role in helping a crawler navigate your own website.
They follow the internal links on your site to discover new pages, which is how they connect your entire site together.
The crawler sends data back to the search engine’s servers as it moves from page to page. This data is then processed and categorised into the search engine index.
The truth is that the entire internet is connected by billions of links.
Web crawlers use these links like highways to navigate and index millions of websites every day.
Note: All good crawlers will review your robots.txt file before entering your website.
A robots.txt file is like a set of rules that website owners can set to tell crawlers which parts of the website they’re allowed to access.
These rules can include not allowing the crawler to access the website at all.
For example, if you don’t want ChatGPT to crawl your site, you can simply disallow GPTbot from entering it.
This would stop ChatGPT from using your information in its AI index.
The five most common different types of crawlers are:
It’s worth noting that large companies own most of the big crawlers. Crawling the internet costs a lot of money and server power.
Smaller businesses generally use crawlers for simple tasks like extracting an email address for outreach or monitoring a competitor’s website changes for SEO.
Web crawlers are often called “spiders” because of how they navigate the internet.
Think of a spider’s web and how a spider moves along it. A web crawler mimics this movement online by navigating from page to page using links.
This creates a “web-like” pattern of movement across the internet.
That’s why you’ll often hear the internet referred to as the “Web”. It’s also why the www. in front of your website domain stands for “World Wide Web”.
Web crawling is about finding, crawling and indexing website URLs and content. Web scraping is just about extracting specific data from websites.
The truth is that web crawling and scraping are different processes for different purposes:
Here’s a list of common web crawlers:
Each of these crawlers does slightly different things and captures different types of information.
Googlebot is by far the most active and sophisticated crawler. Surprisingly, the second largest crawler on the internet is Ahrefsbot.
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