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What are web Crawlers and How do they work?

January 15, 2023

Post by => OneiroAdmin


Web crawlers, spiders, or bots are automated programs that browse the internet to index and archive website content. They visit web pages, read the content, and follow links to other pages to discover new content. The information they collect is used to build and maintain search engines’ indexes, which are used to power the search results you see when you type a query into a search engine. Web crawlers can also be used for other purposes, such as monitoring website changes, scraping data, and identifying broken links.

Web crawlers are extremely important for the functioning of the internet. They are the backbone of search engines, as they are responsible for collecting and organizing the vast amount of information available on the internet. Without web crawlers, search engines could not index and provide relevant results for user queries. Additionally, web crawlers are used by other services, such as analytics platforms, to gather data and insights on web traffic and user behavior.

How does Web crawlers affect SEO?

Web crawlers also play a key role in SEO (Search Engine Optimization), which aims to increase organic traffic to websites from search engines through organic search results. Web crawlers are important for businesses with an online presence as they can help increase visibility and drive traffic to a website. By understanding how web crawlers work and optimizing for them, businesses can improve their search engine rankings and appear higher in search results. This can lead to more visibility for the business and, ultimately, more potential customers finding their website.


Web crawlers automatically visit web pages, read the content, and follow links to other pages. They start with a list of seed URLs; the initial set of URLs the crawler will visit. From there, the crawler will follow the links on each page to discover new URLs.

As the crawler visits each page, it will extract the text and other information from the page, such as the title, meta tags, and images. This information is then indexed and stored in a database, where it can be used to power search results and other online services.

Since there are thousands and millions of web pages to crawl, a specific protocol or algorithm is followed by the web crawlers to determine which pages to crawl, how often to crawl them, and how many pages to fetch from each site. These algorithms consider factors such as the page’s Relevance, the number of links pointing to the page, and the page’s update frequency.

Links and Relevance of the page.

Crawlers crawl web pages according to their importance. Depending on how many other pages link to the page, the amount of traffic the page gets, and other factors, the web crawlers decide which pages to crawl.

The main purpose behind crawling web pages based on the number of links is that web pages with a lot of links get a lot of visitors and have high-quality content; therefore, web crawlers need to index them.

Page’s update frequency

Web crawlers tend to revisit web pages that keep adding, changing or removing content; therefore, they revisit the web pages to ensure that the updated content is indexed.

Robots.txt file

The robots.txt file sets down the rules for web crawler bots. It is basically a way of communicating with web crawlers to let them know which content they can access, and which is not allowed to crawl.

Each search engine’s spider bot weighs these factors differently and behave differently as per their algorithms. Although the ultimate goal of search engine web crawlers is to download and index webpage content.

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