What is a Web Crawler?

Have you ever wondered how the results are listed on a search engine results page? What algorithms or techniques are involved to extract the best content from the trillions of pages and lists in the search results? Well, it’s a web crawler at work! Web crawlers search through the web for the best results and present them to you in an indexed format. 

The same technology works when you collect a user's social network information, given the user's ID. In fact, you come across applications of the web crawler in your everyday life, whether you’re booking an airplane ticket or looking for the best vegetarian restaurant in your neighborhood.

The success of the web crawler for indexing searches or extracting data has made it a popular tool for data scientists, search engine specialists, and scrapers to extract useful information from online sources.

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What is a Web Crawler?  

As the name suggests, the web crawler is a computer program or automated script that crawls through the World Wide Web in a predefined and methodical manner to collect data. The web crawler tool pulls together details about each page: titles, images, keywords, other linked pages, etc. It automatically maps the web to search documents, websites, RSS feeds, and email addresses. It then stores and indexes this data.

Also known as the spider or spider bot, the spider crawl program moves from one website to another, capturing every website. All contents are read and entries are created for a search engine index.

The website crawler gets its name from its crawling behavior as it inches through a website, one page at a time, chasing the links to other pages on the site until all the pages have been read.

Every search engine uses its own web crawler to collect data from the internet and index search results. For instance, Google Search uses the Googlebot.

Web crawlers visit new websites and sitemaps that have been submitted by their owners and periodically revisit the sites to check for updates. So, if you search for the term “web crawler” on Google, the results you get today may differ from what you got a few weeks ago. This is because a web crawler is continually at work, searching for relevant websites that define or describe a “web crawler” in the best manner, factoring in new websites, web pages, or updated content.

How Does the Web Crawler Work? 

The website crawler “crawls” through the web to find the pages of websites to visit, using several algorithms to rate the value of the content or the quality of the links in its index. These rules determine its crawling behavior: which sites to crawl, how often to re-crawl a page, how many pages on a site to be indexed, and so on. When it visits a new website, it downloads its robots.txt file—the “robots exclusion standard” protocol designed to restrict unlimited access by web crawler tools. The file contains information of sitemaps (the URLs to crawl) and the search rules (which of the pages are to be crawled and which parts to ignore).

The crawler tracks each of the links, both internal and external, adding to the next page visited. The process is repeated until the crawler lands on a page with no more links or encounters errors like 404 and 403, loading the site’s contents into a database and the search engine’s index. This is a massive database of words and phrases found on every page, which also defines where the words occur on different web pages. When the search and query function is used, it helps the end-user find the web page with the word or phrase entered.

Traditional Web Crawlers

How a traditional web crawler works

Indexing is an important function of the search engine web crawler. The algorithms interpret the links and their value in the index to give relevant search results.

When you’re searching for a given word or phrase, the search engine will consider hundreds of factors to select and present the indexed web pages to you.

Examples of factors considered are:

  • Quality of the content
  • Content matching the user query
  • The number of links that point to the content
  • The number of times it has been shared online

Major search engines have multiple web crawlers working at the same time from different servers. The process begins with the listing of web addresses from previous crawls and the sitemaps provided by website owners. As the crawlers visit websites, the links found on those sites are used to discover other pages. So now you know why website SEO administrators like to make use of backlinks! Backlinks to your website are a signal to search engines that others vouch for your content.

How Does the Web Crawler Help SEO Experts?

Higher Website Ranking

The SEO expert’s way to higher website ranking 

Search engine optimization is the process of enhancing the quality and frequency of website traffic. This is done by increasing the visibility of a website or a web page to a web search engine.

As you’ve just learned, the SEO implications of the web crawler are huge. The content on a website affects how the website is ranked in the search engine index and optimized for the end-user to see. The better the content, the higher it’s ranked in search engine results.

There are certain components that can improve a website’s ranking in search results. Good content: 

  • Uses keywords that are popular with your audience
  • Is hosted on a fast site with easy navigation
  • Is referenced by other sites as an authority

It’s essential to rank in a high position because many people performing searches don’t go past the first three results. Fewer still will go past the first page of results. If a website does not rank on the front page, it’s practically invisible. Web crawlers will look through your site to evaluate whether it deserves a spot on the first page.

Web crawlers help SEO experts in many stages of website optimization and usability testing. Here are some ways:

Keyword Research, Meta Tags, and Content Optimization

SEO experts know about the algorithms that various search engine crawlers use, including content that enables the indexing of pages with a high ranking.

Web crawlers don’t focus on the words alone, but also record where the words are found. Therefore, the SEO expert makes intelligent use of keywords to get a good ranking. Through experimentation and testing, they learn how to use relevant words in headings, metadata, and the first few sentences, and then they’ll place these keywords in optimized locations.

Handling some of these SEO strategies may require you to seek the help of someone experienced with SEO. For example, meta tags are very helpful for increasing your visibility to search engines. However, it may be difficult for you to figure it out on your own if you have no experience writing code. Meta tags are bits of code that communicate with web crawlers to easily communicate the main ideas of a web page.

Meta tags are also important because they provide the web crawler with information such as the title of your page in the search results. This title and the following description are the first contacts that you will have with the end-user. Taking control of that title and description gives you a chance to draw them in.

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Anchor Linking

By placing new backlinks, additional internal links, and URLs, the SEO professional ensures that the crawlers discover web pages from the links extracted to create the best search results.

Links should be placed in anchor text that includes important keywords in a sentence rather than general words. For example, placing a link over the words “click here” would not be as effective as placing a link on keywords that are important to your content. A good example of strong anchor text for this post would be the words “web crawler.”

Analysis of server logs also provides SEO practitioners with deep insights on how robots interact with the website, which pages they visit frequently, and how many errors are encountered when visiting the website. They can accordingly make appropriate changes for better ranking of the pages in search results.

Sitemap Submission

Placing sitemaps and submitting them to search engines furthers the cause of SEO as sitemaps contain lists of pages to be crawled. Website crawlers can easily discover content that may be hidden deep within the website and do so in a short time thus producing faster, optimized search results.

Social Media Optimization

Social media log analysis helps the SEO professional optimize the keywords, hashtags, and links for higher search results.

Directory and Individual Page submissions 

Each time new content is published, or any updates are made, page submissions made directly to the search engines via their respective interfaces are a useful SEO tool. It ensures the updates get seen by the search engines and that their databases are updated.

Automating website maintenance and optimization tasks

Links can be checked and the behavior of HTML codes can be tracked and validated using the site crawler tool. The SEO health of websites can be checked easily. Email addresses can be mined and harvested to control spamming.

What is Web Crawling Used for? 

Google first began using the web crawler to search and index content as an easy way to discover websites by keywords and phrases. The popularity and diverse applications of indexed search results were soon monetized. Search engines and IT systems created their own web crawlers programmed with different algorithms. These crawled the web, scanned content, and created a copy of the visited pages for subsequent indexing. The result is visible, as today you can find any information or data that exists on the web.

We can use crawlers to gather specific types of information from web pages, such as:

  • Indexed reviews from a food aggregator app
  • Information for academic research
  • Market research to find the most popular trends
  • Best services or locations for personal use
  • Jobs or opportunities in business

Web crawler uses in the field of business intelligence include:

  • Tracking changes in content
  • Detecting malicious websites
  • Automated price retrieval from competitor websites for pricing strategy
  • Identifying potential bestsellers for an e-commerce platform by accessing data from the competition
  • Ranking popularity of leaders or film stars
  • Access data feeds from thousands of similar brands
  • Indexing most frequently shared links on social networks
  • Access and index job listings based on employee reviews and salaries
  • Zip code-based price benchmarking and cataloging for retailers
  • Building a service review database by aggregating scattered reviews across multiple sources
  • Extracting data from news agencies and social feeds for breaking news, used for generating automated content
  • Accessing market and social data to build a financial recommendation engine
  • Discovering terrorist-related chat rooms
Are you skilled enough to help your website top the search engine ranks? Well try answering these SEO Online Test Questions and find out now!

Get Insight Into Web Crawlers with Our SEO Training Course 

A web crawler is a powerful tool not only for your personal searches, but also to generate powerful insights for businesses to remain competitive. Knowing how the web crawler works and how to leverage it for your goals gives you a head start in both your daily life and work. Whether you’re an SEO expert, a website administrator, or a data scientist, a web crawler learning curve is a useful tool in your work.

Learning to build a web crawler customized to your business requirements is a powerful career add-on to your portfolio. As web crawling and scraping involves certain protocols and best practices, it’s best learned through formal training by a certified IT expert.

So, what are you waiting for? Go ahead and register for an SEO training course that will give you a leg-up in this fast-changing technological landscape.

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Simplilearn is one of the world’s leading providers of online training for Digital Marketing, Cloud Computing, Project Management, Data Science, IT, Software Development, and many other emerging technologies.

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