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Web Crawlers: What are they and How Do They Work?

This is how the Google bot crawls the entire internet.

To understand how the internet works, we must first understand programs called web crawlers. If you are visualizing a spider in your head, from the various times you might have heard this word before, then you are correct. Another name for web crawlers is indeed spiders.

“Where there is a web, there is a spider” (Jhala, 2017)

The internet being the biggest web of all, there is not one but several spiders. Every search engine in the world employs crawler bots to help find whatever information you are looking for. It is hard to imagine the amount of information web crawlers go through, to create comprehensive indexes that can make the searching of any information on the internet easier and faster for all of us. Let us first understand the two main processes that crawlers are involved in before we go any deeper.


Crawling and Indexing:

Web crawling is eerily similar to what one imagines when they hear the word “crawling”. An army of spider bots is employed by search engines such as Google to crawl through web pages, containing both those that have been crawled in the past as well as those that have been newly added to the topography of the digital medium. Outbound links are the main highways that these crawlers use to visit different websites from the already crawled pages. Then they will crawl through the page they were sent to by following the said links. Obviously, simply visiting these pages accomplishes nothing. The second half of this act is indexing. An index is a list of information that can be accessed to find the exact information one is looking for in a larger repository of data.

Hold on! What’s that? – Indexing

Every book you had in school had an index in the beginning that told you the page number you could directly flip to if you were interested in reading about just one topic in the book. In the same manner, the crawler bot goes on compiling the information it finds on webpages. It then encodes this information to make it more compact for easier storage. These indexes are stored on servers maintained by Google, when you type in a word or a string of words in the Google search console, they spring into action. So, they are working pretty much non-stop.


Ranking or Weighing

Next comes the process of sorting through these stored webpages to figure out which pages are the most relevant to your search terms. Google and other prominent search engines such as AltaVista and Yahoo use highly sophisticated software to sort through these indexes and rank the top webpages based on their traffic and original content among other things. These algorithms constantly keep updating the rankings as the relevance of a webpage goes up and down with time.

Writopedia Fact File: To get some idea as to how complicated this process really is, let us examine the quantity of data web crawlers index. In 2008 there were about 1 trillion web pages on the internet according to Google which in 2013 had grown to 30 trillion. This year, it has again grown to 130 trillion web pages hosted on over 1 billion websites. These are massive amounts of data that web crawlers must index for the World Wide Web to be of optimum use. Additionally, they must also ensure that any overload is avoided as far as the servers indexing the data are concerned, so they encode all this information into much smaller and easily traceable bits of information.


The Sacred Robots.txt File

Does this mean web crawlers know everything that happens on the internet? No. There is a protocol that was decided upon in the early stages of the internet called robots.txt. It enables you to direct web crawlers away from content you do not want them to index. This could be for several reasons including privacy, or the fact that the page in concern is constantly changing information. in that you regularly update it and do not want any outdated versions to be stored in the indexes. Using robots.txt and sitemaps, web crawlers can be guided to navigate specific parts of your website, especially by preventing them from indexing any information you do not want found anywhere but on your website. The only precaution you must take is to ensure there are no inbound links to your page anywhere else, especially if you do not want these web pages to be discovered by the crawlers. This is because crawlers are “bound by code” to follow any outbound links on the web pages that it crawls, especially if they are not regulated by the robots.txt file.


Summoning the Crawler

Crawlers do not merely require outbound and inbound links to travel between web pages, they can actually be summoned to visit your website. Google Search Console, which was formerly known as the Google Webmasters Tool, comes in handy while summoning a spider bot. The Google Search Console, if used in the right way, can allow you to look at your website from the eyes of Googlebot, which is the crawler that the search engine uses for the purpose of indexing web pages. In other words, this can allow you to understand the various aspects that might need changing on your website so that you can ensure they are properly indexed. On the other hand, you can also work on improving the loading speed of your pages so that you are judged well in the eyes of Google as far as quality and worthiness of your website are concerned. You can even increase your crawl rate according to the rate at which you update content on your website.


Customizing your Own Crawler

Looking at this from your angle, can you use crawlers to find specific information on the internet?

Why, yes you can!

Crawlers are not very difficult to create as long as you know what you are looking for. Just like Google employs web crawlers to catalogue all the accessible information on the internet, you can employ crawlers to find information specifically about, say, rockets. It is essentially a Google search you are doing, but choosing for yourself what you want to prioritize and what you don’t. When you input a search query on Google, the search engine gets to decide which links to show first based on its own sorting filters that partially use your own browsing history and preferences saved in your Google account. But when you create your own crawlers, you don’t need to worry about any sort of bias that could be in-built into Google’s code or the generalized search optimization that Google is bound to apply to your query. Instead, you can choose to find web pages that will have the most reliable content concerning the creation of a rocket, such as PhD dissertation papers done by doctoral candidates at MIT and Stanford and within these web pages you can further differentiate between those that contain completely original content and those that are based on other research.

Food for Thought: If web pages are ranked as per certain parameters such as quality of content, types of keywords used, and so on, what do you think the raw pages indexed by the crawlers (stripped of all their glorious ranks and segregated without bias) are valued or weighed by? Find the answer

Imagine the applications of this knowledge. Crawlers designed to find the most specific information and do it as quickly as search engines do it, through indexing. All you would need is some coding skills and an idea of exactly what to look for and how to look for it. You could potentially create crawlers so sophisticated that you could disrupt entire fields of business. Ironically enough, Search Engine Optimization is one of them.