What is a web crawler?

A web crawler is an automated program, script, or bot that helps search engines and other programs keep up with the constantly changing content on the internet, ensuring you always have access to the latest information.

For example, when a search engine like Google or Bing delivers pages matching your query, a crawler actively gathers and indexes those pages behind the scenes. 

How do web crawlers work?

The website crawling workflow influences how quickly sites are processed and how thoroughly their content is analyzed. So, whether you want potential customers to easily find your business online or wish to stay informed of crucial developments, understanding clearly how they work can help you make the most of the internet's opportunities. Here are the steps involved:

• Seed URLs: Crawlers begin with a list of starting URLs, known as seeds, which are usually popular domains or pages you want to prioritize indexing for your site.

• HTTP requests: The bots then make HTTP requests to fetch pages at those seed URLs and discover new links to other pages on your site.

• Content download: They download each page's content, including text, images, and other files, for parsing and storage.

• Parsing: Specialized software extracts metadata from your pages and articles, such as titles and descriptions, identifies links, and analyzes the content for searchability and relevancy.

• Link discovery: Crawlers find all internal links on your pages and external links to other domains to discover the full extent of the publicly available web.

• Prioritization: Algorithms determine the importance and authority of each page based on on-page factors like keywords and phrases and off-page elements such as the number of inbound links from other highly relevant pages. Higher priority pages are added to the crawl queue sooner for indexing.

• Revisit scheduling: Crawlers are programmed to revisit pages on a set schedule, ranging from daily for frequently updated sites to annually for more static ones.

• Data storage: All extracted data is stored in massive databases that are then used to serve search results.

• Respecting robots.txt: Your website includes a robots.txt file in its root directory that crawlers will check before indexing. This document allows you to specify specific directories or page types that crawlers should avoid, letting you maintain control over what content is accessible through search.

• Handling dynamic content: JavaScript, cookies, and caching on your site make it challenging for crawlers to render dynamic pages fully. These bots try to support this content by executing JavaScript, replicating user sessions through cookies, and employing techniques like hash-based revalidation to check for updates without unnecessary prefetching.

Types of web crawlers

Different crawlers explore your pages for a wide range of reasons. By understanding the most common types, you can better optimize how your online content is accessed and discovered, boosting traffic and leads. It’s also valuable for defending yourself against malicious crawlers. Let's explore some of the most notable kinds:

• Search engine crawlers: Powerful bots like those from Google and Bing regularly scan websites to keep search results relevant by indexing fresh pages and updates in a timely manner.

• SEO crawlers: Search engine optimization (SEO) services like Ahrefs employ specialized crawlers to identify on-page technical issues and off-page link opportunities to help with optimization strategies.

• Data mining crawlers: Market researchers and analytics firms use custom bots to aggregate publicly available online data, gaining insights into trends, user behaviors, and competition.

• Price comparison crawlers: Price comparison sites use real-time crawlers to monitor price changes across e-commerce retailers, ensuring shoppers see the best deals.

• Academic crawlers: Researchers in fields like natural language processing and web structure analysis craft tailored bots to collect public data for their studies.

• News aggregator crawlers: Services that curate news headlines rely on crawlers to discover, verify, and share up-to-date information from publisher websites.

• Social media crawlers: Platforms like Facebook employ crawlers to scan social profiles for shared links to understand engagement and inform advertising.

• Malicious crawlers: Unfortunately, some crawlers are used for illegal activities, such as spreading malware, stealing credentials, or enabling Distributed Denial-of-Service (DDoS) attacks.

Challenges and considerations of web crawling

While these bots provide many benefits, their operations can also give rise to complications, impacting both crawler operators and your website. To overcome these obstacles, it's essential to understand the potential roadblocks for responsible crawling and effective online content and platform management.

Below are some common issues:

• Server load: Frequent crawling can strain your servers with numerous requests, potentially degrading performance for site visitors if left unchecked.

• Bandwidth consumption: The transmission of crawl data eats up your capacity and resources. If there are limits put in place by your web hosting company, your website performance could be throttled once you hit the thresholds.

• Privacy concerns: If crawlers collect and distribute sensitive personal information from your site, they raise issues around data protection.

• Intellectual property issues: These bots sometimes infringe on copyright by copying and sharing proprietary images, text, or code.

• Crawler traps: Complex pages on your site confuse crawlers, causing wasted processing on unintended or infinite loops.

• Duplicate content: Identical or near-identical pages on your platform or across the web present challenges for crawlers to properly distinguish.

• Crawl budget management: Due to processing limitations, ensuring essential pages on frequently updated sites are crawled efficiently can be challenging. Crawlers must prioritize domains and content types to effectively index high-value information within these constraints.

• International and legal considerations: Regulations differ globally, so crawlers need policies respecting local jurisdiction over data practices and ownership rights.

• Ethical considerations: Automated crawling activities should avoid unintended consequences like sharing copyrighted information by implementing more thoughtful technological development and oversight.

10 best practices for managing crawlers on your website

Effectively managing how automated programs discover your website requires a strategic approach to maximize the benefits of crawling while minimizing potential issues. Implementing such a strategy helps reduce bandwidth costs, enhances customer experience, and increases lead generation by improving page discoverability. Here are key approaches to consider:

1. Implement robots.txt

Place a robots.txt file in your domain's root folder to manage crawler preferences. Create a plain text file named robots.txt and specify rules using the User-agent and Disallow directives.

2. Create XML sitemaps

Many CMS platforms provide sitemap plugins. For WordPress, consider Yoast SEO, RankMath, or Google XML Sitemaps to auto-generate sitemaps for your content.

3. Use meta robots tags.

Apply tags like or to pages you don't want crawled or followed. In WordPress, these can be managed from each page/post's SEO settings.

4. Monitor crawler activity

Tools like server logs help you track bots, ensuring legitimate indexing and identifying any misuse or attacks. A CDN can also monitor and analyze access patterns.

5. Optimize crawl budget

Improve page speeds and minimize duplicate content so crawlers focus on valuable pages. Use tools like Google's PageSpeed Insights or GTmetrix for site audits to identify performance issues.

6. Implement proper HTTP status codes.

Return appropriate codes such as 4xx for unauthorized access and 5xx for errors to clearly communicate page status. Ensure your server configuration supports accurate code responses.

7. Manage duplicate content

Consolidate near-identical pages to avoid diluting relevancy. Tools like Xenu can identify redundant pages for cleanup or canonical tagging.

8. Control crawl rate

If spikes occur, robots.txt or server config allows pausing indexing temporarily to protect resources from overload. You can also adjust crawler speed settings with search engine tools.

9. Secure sensitive content

Ensure any private pages require authentication, so crawlers don't collect and distribute passwords or personal details. Also, check for forms that secure submitted information.

10. Stay updated on crawler developments.

Monitor forums to stay informed about evolving best practices and balancing crawler needs with responsible website management. 

Use Fastly to streamline crawler management and bot protection.

As we have seen, crawlers help your business share information and connect with interested audiences. However, managing them presents real considerations, such as server loads, duplicate content, and other challenges that must be addressed. With various types of crawlers, each serving unique goals, overseeing interactions demands a subtle approach.

Fastly's bot management solutions help streamline this process by protecting your websites from malicious crawlers attempting attacks or scrapings. You gain the following benefits and features by using the platform:

• Bot detection: Fastly's solutions identify and categorize different automated programs that interact with websites accurately.

• Traffic filtering: The platform distinguishes between well-known crawlers and potentially harmful bots based on attributes like source IP and behavior patterns.

• Rate limiting: Fastly allows adjusting the rate at which various crawlers and bots can access resources, helping balance legitimate needs while avoiding overloads.

• Custom rules: You can implement and tailor specific policies for different classes of crawlers based on their capabilities.

• Real-time analytics: Fastly provides insights into your website crawling activity to help you understand its impact on performance and inform rule optimization over time.

• API protection: The solution strives to secure your APIs from crawlers' unauthorized access.

• CAPTCHA integration: For questionable traffic, Fastly allows you to challenge suspicious crawlers to verify legitimate intent before further access is permitted.

• Adaptive security: Fastly's continuous learning aims to help stay updated on new crawler types and behaviors through shared intelligence in a responsible manner.

Ready to optimize your crawler interactions and online security? Schedule a Fastly demo to learn how this solution helps balance discoverability with safeguarding resources.