Some modern web crawlers can process JavaScript and follow links embedded in it, but not all of them do.
A web crawler is an automated program or bot that systematically searches websites and indexes the content on them. Primarily used to index pages for search engines, web crawlers are also used for coupon and comparison shopping apps, and SEO and RSS aggregation, among other tasks. Web crawlers access sites via the internet and gather information about each page, including titles, images, keywords, and links within the page. This data is used by search engines to build an index of web pages, allowing the engine to return faster and more accurate search results for users. Web crawlers may also be used to scrape or pull content from websites, monitor changes on web pages, test websites, and mine them for data. Web crawlers are also known as web spiders since they crawl pages on the World Wide Web.
How do web crawlers work?
Web crawlers start by crawling a set of known pages and following hyperlinks to new pages. Before crawling a site, web crawlers review the site’s robots.txt file, which outlines the rules the website owner has established for bots about which pages can be crawled and which links can be followed.
Because crawlers can’t index every page on the internet, they follow certain rules to prioritize some pages over others. Crawlers may be instructed to give more weight to pages that have more external links to other pages, to sites with a higher number of page views, and to sites that have greater brand authority. Search engines assume that pages with lots of visitors and links are more likely to offer authoritative information and high-quality content that users are looking for. Crawlers also use algorithms to rate the value of content or the quality of links on the page.
As web crawlers explore websites, they copy each site’s meta tags, which provide metadata information about the site and the keywords on it. This data helps search engines determine how a page will show up in search results.
How do web crawlers impact SEO?
Search engine optimization is the practice of making a website more visible to the users who are searching for the type of content, products, or services on the site. Sites that can’t be crawled easily will have lower rankings on search engine results pages (SERPs). Sites that can’t be crawled at all will not appear in the results pages. To improve search engine rankings, SEO teams eliminate errors on websites like missing page titles, duplicate content, and broken links that make sites more difficult to crawl and index.
What are types of web crawlers?
There are four basic types of web crawlers.
- Focused web crawlers search, index, and download web content concerning specific topics. Rather than exploring every hyperlink on a page as a standard web crawler would, a focused web crawler only follows links perceived to be relevant.
- Incremental crawlers revisit websites to refresh an index and update URLs.
- Parallel crawlers run multiple crawling processes at the same time to maximize the download rate.
- Distributed crawlers use multiple crawlers to simultaneously index different sites.
What are examples of web crawlers?
Most search engines use their own web crawlers that operate based on specific algorithms. Companies may also deploy their own web crawler software on-premises or in the cloud. Some of the most common crawlers include:
- Googlebot, the crawler for Google’s search engine
- Bingbot, Microsoft’s search engine crawler
- Amazonbot, the Amazon web crawler
- DuckDuckBot, the crawler for the search engine DuckDuckGo
- YandexBot, the crawler for the Yandex search engine
- Baiduspider, the web crawler for the Chinese search engine Baidu
- Slurp, the web crawler for Yahoo
- Coupon apps, like Honey
What is web crawling vs. web scraping?
Web crawling is the task of finding and indexing web pages. Web scraping uses bots to extract data found on web pages, often without permission. Web scrapers often use AI to find specific data on a page, copying it for use in analytics software. Use cases for web scrapers include ecommerce companies tracking their competitors’ price points, government agencies performing labor research, or enterprises performing market research. Common web scraping tools include Bright Data, Scrape.do, Diffbot, and Scrapy, an open source and collaborative framework for web scraping.
How do web crawlers affect bot management?
Bot management is the practice of identifying and managing bot traffic on websites and online applications. While bots like web crawlers are beneficial, many bots are malicious in nature and should be blocked from accessing websites and applications. When implementing bot management technology, it’s important to choose solutions that can carefully and accurately distinguish between good bots and bad bots. Solutions that indiscriminately block productivity may inadvertently block web crawlers, reducing the website’s search engine rankings.
Often, companies prefer some web crawlers over others; for example, they may want to be indexed by Googlebot and Bingbot but not some smaller search engines. Or they may be fine with search engine web crawlers but not those used by coupon and comparison shopping apps. Some bot management solutions allow companies to take different actions on individual web crawlers based on their own goals so they don’t simply have to accept all web crawlers that want to index their site.
Frequently Asked Questions (FAQ)
Web crawlers visit websites regularly, with the frequency depending on various factors like the website’s update frequency and its importance.
Yes, you can use a robots.txt file to instruct web crawlers on which parts of your site to crawl and which to ignore. You can also set preferences in some more sophisticated bot management solutions to take different actions on different web crawlers, like allowing some lesser-known web crawlers to only access your site during overnight hours, for example.
You can use search engine-specific tools like Google Search Console to check if your website has been indexed.
Web crawlers can read image and video metadata but may not interpret their content as comprehensively as text.
In most cases, web crawlers cannot access content behind login walls or password-protected areas.
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