Web crawlers collect information throughout billions of webpages and categorize it in a search index. It begins with a directory of web addresses from the previous crawls and site maps provided by the web owners. Crawlers use links on those websites to find other pages as they visit. Computer programs decide how regularly to visit and how many pages they should take from each site then decides which sites to crawl.
Before we dig deep, let us understand first some basic terms.
Search Engine Optimization or SEO – the system of increasing the number and quality of the traffic to your website through organic search engine results.
Web crawler – Also known as a web spider or web robot. It is a computer program used by the search engine to index the web content of other websites the duplicate webpages so they can be processed afterward by the search engine.
Web crawling – is the process by which data is gathered from the web in order to index and assist a search engine. The objective is to gather as fast and effectively as many useful and potential web pages with the link structure that connects them.
How does it work?
1) Find URLs – Building a clear site map and constructing an easily maneuverable are good ways to inspire search engines to crawl your website.
2) Discover list of seeds – search engines provide its web crawlers a record of web addresses to find out. The web crawler searches for each URL on the list, which is identified as seeds, and classifies all of the links on each page, and includes them to the URLs to visit.
3) Index Update – the web crawlers try to understand what a page is about by noting key signals such as keywords, content, and the originality of the content. As per Google, “The software pays special attention to new sites, changes to existing sites, and dead links.”
4) Frequency of crawl – Web crawler is doing its job and crawling the internet 24/7. According to Google, “Computer programs determine which sites to crawl, how often and how many pages to fetch from each site.”
5) Block web crawler – You can prevent web crawlers from indexing your website if you choose to by using robots.txt file which is like telling the web crawler “no entry”. Web crawlers will not crawl if they find a status code in your HTTP header transmitting that the page does not exist.
