What Is Web Crawling?


    Web crawling refers to the process of browsing and indexing web pages to help users find relevant information. Without it, SEO would be obsolete, and people would have a tough time finding the content they need.
    But what is web crawling exactly? Let’s find out.

    Defining a Crawler

    To answer the main question, what is web crawling, it’s easy to understand it as a web spider, which is an internet bot that uses computer algorithms to search through the web. It’s a computer program that systematically indexes web pages to help search engines learn more about them. It’s like creating a library of all online content.
    When a search engine “understands” what a website is about, it can determine if it’s relevant to a particular search query.
    Without web crawlers, search engines wouldn’t have an insight into any website. It would be as if they didn’t exist at all. Therefore, they wouldn’t show up in SERPs.
    Search engines wouldn’t know where to start looking to give us the answers we seek. After all, there are trillions of web pages out there. You can find more information about web crawlers.

    How Does a Crawler Work?

    Crawlers primarily examine links on a web page that lead them to other pages. They then explore those pages and their URLs, too, before crawling the other pages they lead to, and so on.
    They also look at the entire website copy, as well as meta tags, such as meta title and meta description. Collecting that information helps search engines organize the pages for keywords.
    Because of a colossal number of web pages, this whole process would go on and on without specific indexing rules.
    The two most important rules that web crawlers use include:


    Revisiting policy
    What makes a website relevant? High-quality content that addresses users’ pain points, helping them find the right answers they need.
    When a website features such content that provides excellent user experiences, it gets more visitors.
    So, crawlers look at the number of visitors, the time spent on every page, bounce rates, and many other factors. They also look at other pages citing a particular page.
    If there’s a lot of them, and the page attracts plenty of visitors, they deem it relevant, credible, and authoritative. It’s how search engines rank websites and recommend them for proper search queries.

    Revisiting Policy

    Web spiders use a revisiting policy to ensure the web index contains up-to-date information.
    That’s crucial for all updated content and relocated pages. If there’s any change, crawlers will update the index.

    What If a Page Doesn’t Link to Other URLs?

    Let’s say you’ve just launched your website and, for some reason, don’t want to link to other sites. Does that mean the internet bots can’t crawl and index it?
    Not exactly.
    You can put in a crawling request by submitting your site to search engines.
    That way, the bots will index your site, and search engine algorithms will look for keywords to properly sort your pages.
    But you should seriously consider linking to external pages, as it’s vital for effective SEO.
    Spider bots can find and crawl your site, but they can’t determine its relevance, credibility, and authority without links.

    Different Types of Crawlers

    Web crawlers can do much more than simply index sites. They can also help with other types of data mining.
    So, apart from search engine crawlers, you have:
    Image crawlers
    They crawl images using relevant keywords so that search engines can easily retrieve them.
    Video crawlers
    Similar to image crawlers, video crawlers index video content. If you embed videos on your site, you can help with their indexing by adding metadata.
    Social media crawlers
    Twitter and Pinterest are some examples of social platforms that allow content crawling. However, they allow it only if it doesn’t violate privacy, such as extracting personal data.
    News crawlers
    These spider bots sift through all the news available online. They extract URLs, articles, authors’ names, publishing time and language, lead paragraphs, and headlines.
    There are also email crawlers, but they’re illegal. They can find email addresses, but that’s in direct violation of privacy.

    Examples of Crawler Use

    You may have heard about Googlebot, which is the most popular search engine crawler. It actually features two bots: Googlebot Desktop and Googlebot Mobile.
    However, since Google isn’t the only search engine, it’s quite logical that there are other spider bots out there.
    The most common examples are:
    Baidu Spider
    Yahoo! Slurp
    Yandex Bot
    Sogou Spider
    Facebook External Hit
    There are also numerous open-source crawlers that you can use to mine data, such as JSpider, PHP-Crawler, Nutch, and Scrapy.


    Web crawling is crucial for the visibility of online content. It plays a big part in search engine optimization, so you shouldn’t block crawlers.
    Allowing them to crawl and index your site will help you rank higher in SERPs and drive more organic traffic.