What Is a Web Crawler: A Guide to Crawling

Web crawlers — also known as “crawlers,” “bots,” “web robots,” or “web spiders” — are automated programs that methodically browse the web for the sole purpose of indexing web pages and the content they contain. Search engines use bots to crawl new and updated web pages for information to add to their index so that when individuals search for a particular query, the most relevant information can be easily accessed and served.

Types of Web Crawlers

Google is most known for its web crawler Googlebot, but there is also an array of other site-specific web crawlers. By understanding the different types of crawlers, you can better adhere to them. Examples of other site-specific web crawlers include:

Baidu Spider;
Bingbot;
Yandex Bot;
Soso Spider;
Exabot;
Alexa Crawler.

How Do Web Crawlers Work?

Crawlers seek out information that is put on the World Wide Web. The internet changes daily, and web crawlers follow certain protocols, policies and algorithms to make choices on which pages to crawl, as well as which order to crawl them in. The crawler analyzes content and categorizes it into an index in order to easily retrieve that information for user-specific queries.

Relevant information is determined by algorithms specific to the crawlers, but typically include factors like the accuracy, rate, and location of keywords. Although the exact mapping of how this works is specific to the algorithms used by proprietary bots, the process typically follows as such:

- The web crawlers are given a URL (or multiple);
- Crawlers skim through a page’s content and essentially take notes on it — what it’s about, whether it’s advertorial or informational, what kind of keywords it uses — so that they can categorize it as accurately as possible;
- This data is recorded and added to a giant archive, unique to the search engine, called an index. When a user submits a query, search engine algorithms sort through the data in this index to return the most relevant results.
- After their targets are indexed, crawlers identify outbound hyperlinks, then follow them to other pages, repeating the process ad infinitum;

Why Do I Want My Website Crawled?

While many think that when you publish a post on a website it will automatically be displayed to everyone searching for it through Google or Bing, this is not the case. First, your web page needs to be indexed. In order for a web page to be indexed, it must first be crawled. Getting crawled is a necessity because it — and a number of search engine-specific algorithms — determines whether or not your website will get indexed.

Crawling vs. Scraping

Web crawling is often misconstrued with web scraping. Web scraping differs from web crawling by the way that it extracts and replicates specific information from anywhere that data exists (i.e content, pricing) while web crawling scans pages for indexing. Crawling is typically done on a larger scale while scraping is less intricate. Web scraping is commonly associated with black hat SEO techniques, though it shouldn’t necessarily be; web scraping can and is used in a number of white hat SEO strategies and by data scientists.

In most cases, the process of getting indexed is inevitable. However, there are ways that you can improve your site’s visibility in the index:

Technical SEO: A website’s technical features interact directly with search engine crawlers, so an analysis of the ways in which your article performs well and which ways your article performs poorly can help search engines to crawl and index your site more optimally. A good tool for reference is Google’s general guidelines;
Blocking Links: Although you do want bots to crawl your page, webpage administrators can exclude specific pages of their websites from crawling via their robots.txt file. This leads bots through the website by telling them which pages to crawl, and which pages to stay away from through the robots exclusion protocol (REP). Having control over which pages or subfolders are allowed or disallowed is important in preventing bots from accessing all parts of a domain. Robots.txt is utilized in order to avoid crawling occurrences such as; crawling duplicate information, indexing specific files (images, blog posts, etc.), and to keep an internal SERP from being indexed;
Sitemap Inclusion: Your sitemap acts as a literal map for bots to understand what pages are on your site. While simply putting a page in your sitemap doesn’t ensure getting indexed, it’s much more likely to be if it is.

There are some cases where bots will crawl a website but ultimately will not index it. Follow these steps to check whether your webpage is indexed or not:

Use a “site:domain.com” Query: This shows users the URLs for a domain that Google has indexed (i.e. site:pageonepower.com);
Examine the Index Status Tool: This report offers the state of indexing for all web pages that Google has visited.

Why Google has decided not to index a web page is typically a simple and quick fix. Some reasons why your website is not being indexed could include:

New Website: If you have just launched your website, there is a chance Google hasn’t gotten to it yet. There is not a set timeline determining how long it takes to get indexed; it can vary anywhere from 4 days to 4 weeks;
Bad Content: If a crawler goes through a webpage and sees things such as irrelevant content, keyword stuffing, duplicate content, etc. it will sometimes decide not to display your page as a result;
Competitive Subject: There are billions of websites active in search engines; if you are writing about a very popular topic, it will be harder to provide unique, worthwhile information that another page hasn’t already covered (especially if it has been active longer);

The best way to get a good glimpse of factors that are affecting crawlability and indexability is by taking advantage of site auditing services. Site audits build the foundation for the success of a webpage by analyzing potential factors that may be holding your website from its full potential.

What is a web crawler?

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