Are You Using Web Crawlers to Your Advantage? Essential Guide to Gain SEO Success

Are Malicious Bots Secretly Harming Your Website’s Ranking? Here’s How to Fight Back.

For any business with a website, staying visible is crucial. You might spend a lot of time creating new blog posts, updating product pages, or refining your services. The goal is to keep your site fresh and improve its ranking on search engines like Google. However, if your website has hundreds or even thousands of pages, telling search engines about every single update manually is impossible. How do you make sure your hard work actually gets seen and improves your search ranking?

This is where web crawlers come in. Think of a web crawler as a librarian for the internet. The internet is a library with billions of books (websites), and it has no central filing system. A crawler’s job is to go out, read every book, and create a massive card catalog (a search index) so that when someone asks a question, the librarian can quickly find the most relevant answers.

These crawlers, also called bots or spiders, scan your website’s map (sitemap) and pages for new updates. They then report this information back to search engines to be indexed. Without this process, your website is invisible. Many factors affect your site’s SEO ranking, such as the quality of your content, links from other sites (backlinks), and your web hosting. But none of that matters if crawlers cannot find and read your pages. Making your site easy for the right crawlers to access is the first and most vital step to online success. This is especially true for topics related to “Your Money or Your Life” (YMYL), where search engines prioritize content from trustworthy and authoritative sources.

How Does a Web Crawler Actually Work?

A crawler’s work is a constant, four-step cycle. Understanding this process helps you see your website from a search engine’s perspective and optimize it correctly.

Step 1 Discovery: Finding Your Pages

A crawler doesn’t magically know your website exists. It needs a starting point. It discovers new pages and sites in a few key ways:

• Known URLs: The process begins with a list of web pages that are already known and trusted. These are established sites with a history of quality.
• Backlinks: When a known website links to your website, it creates a pathway. The crawler follows this link, discovering your page as a new destination. This is why getting links from reputable sites is so powerful.
• Sitemaps: You can create a file called an XML sitemap, which is a list of every important page on your website. Submitting this map directly to search engines (like through Google Search Console) is like handing the librarian a table of contents for your site.

Step 2 Crawling: Reading the Content

Once a crawler discovers a URL, it visits the page and downloads its content. This isn’t just the text you see. It includes the underlying HTML code, CSS style sheets, and JavaScript files. The crawler essentially saves a copy of everything that makes up your page. It also looks for new links on that page to add to its list of places to visit next.

Step 3 Rendering: Seeing What a User Sees

Modern websites are complex. Much of the content you see might be loaded by JavaScript after the initial page loads. In the past, crawlers only read the raw HTML and would miss this dynamic content. Today, major crawlers like Googlebot are much smarter. They can render the page, which means they execute the JavaScript and CSS to see the page just as a human user would in their browser. This is a critical step. If your important text or links only appear after a complex script runs, you need to ensure crawlers can render it properly.

Step 4 Indexing: Storing the Information

After a page is crawled and rendered, the information needs to be processed and stored. This is called indexing. The crawler extracts key information from the page:

• The page title and main headings.
• The text content and keywords it contains.
• Images and videos.
• Links on the page.

This processed information is then stored in a gigantic, highly organized database called the search index. When a user types a query into a search engine, the algorithm doesn’t search the entire live internet. It searches this pre-built index, which is why results appear in milliseconds.

Controlling Crawlers with robots.txt

As a website owner, you have a degree of control over this process. On your server, you can use a file named robots.txt. This file gives crawlers instructions about which parts of your site they should or should not visit. For example, you might block crawlers from accessing private login pages, internal search results, or duplicate content.

It is important to understand that robots.txt is a guide, not a wall. Reputable crawlers will follow its rules, but malicious bots will ignore it completely. Furthermore, blocking a page with robots.txt only prevents it from being crawled. If another site links to that page, it might still appear in search results (without a description). To truly keep a page out of the index, you must use a noindex tag in the page’s HTML.

The Different Kinds of Web Crawlers

As you build a list of bots to monitor, it helps to group them into types. Understanding who built a crawler tells you a lot about its purpose.

Search Engine Crawlers

These are the most important bots, built by companies like Google, Microsoft (Bing), and Yandex. Their sole purpose is to index the web for public search engines. Their activity is a sign of your site’s health and visibility.

Commercial Crawlers

These bots are part of paid SEO tools like Ahrefs, Semrush, and Moz. Companies use these tools to audit their own sites, analyze competitors, and find backlinks. These crawlers gather data to sell back to you as insights.

In-house Crawlers

Large corporations like Amazon or eBay often build their own crawlers. These are designed for specific internal tasks, such as monitoring prices on competitor sites or auditing their own massive inventories.

Open-Source Crawlers

These are crawlers built from freely available frameworks like Scrapy and Nutch. Developers and researchers use them to build custom crawlers for data mining, academic research, or other specialized projects.

The 14 Most Common Search Engine Crawlers

There isn’t one bot that powers every search engine. Each one has its own crawler with a unique purpose. Here are the most common ones you will see in your server logs.

Googlebot

The most famous and active crawler in the world. Googlebot is responsible for indexing content for Google Search. It has two main versions: Googlebot Desktop and Googlebot Smartphone, reflecting the shift to mobile-first indexing. It visits most sites every few seconds and stores backups in Google Cache, which allows you to see older versions of pages.

Full User Agent String of Googlebot:

Mozilla/5.0 (compatible; Googlebot/2.1; +http://www.google.com/bot.html)

Bingbot

Created by Microsoft, Bingbot crawls the web for the Bing search engine. As Bing powers search for other platforms like DuckDuckGo and Yahoo, Bingbot’s reach is wider than many realize. You can monitor its activity and submit sitemaps through Bing Webmaster Tools.

Full User Agent String of Bingbot: 

Desktop:

Mozilla/5.0 AppleWebKit/537.36 (KHTML, like Gecko; compatible; bingbot/2.0; +https://www.bing.com/bingbot.htm) Chrome/W.X.Y.Z Safari/537.36

Mobile:

 Mozilla/5.0 (Linux; Android 6.0.1; Nexus 5X Build/MMB29P) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/W.X.Y.Z Mobile Safari/537.36 (compatible; bingbot/2.0; +https://www.bing.com/bingbot.htm)

“W.X.Y.Z” will be substituted with the latest Microsoft Edge version Bing is using, for eg. “100.0.4896.127″

Yandex Bot

This is the primary crawler for Yandex, Russia’s largest search engine. If you want to reach the Russian market or audiences using Cyrillic languages, allowing Yandex Bot to crawl your site is essential.

Full User Agent String of Yandex Bot: 

Mozilla/5.0 (compatible; YandexBot/3.0; +http://yandex.com/bots)

Apple Bot

This crawler powers results for Apple’s ecosystem, including Siri Suggestions and Spotlight Search on iPhones and Macs. It considers factors like user engagement and location to provide personalized recommendations. Its influence is growing as more people use Apple’s built-in search features.

Full User Agent String of Apple Bot: 

Mozilla/5.0 (Device; OS_version) AppleWebKit/WebKit_version (KHTML, like Gecko)
Version/Safari_version Safari/WebKit_version (Applebot/Applebot_version)

DuckDuckBot

The web crawler for DuckDuckGo, a search engine focused on user privacy. While DuckDuckGo gets many of its results from Bing, its own bot helps it refine and supplement its index.

Full User Agent String of DuckDuckBot: 

DuckDuckBot/1.0; (+http://duckduckgo.com/duckduckbot.html)

Baidu Spider

Baidu is the dominant search engine in China. Because Google is blocked there, Baidu Spider is the only crawler that matters if you want to reach the massive Chinese market. If you do not do business in China, you might consider blocking this bot, as its traffic can be irrelevant and add load to your server.

Full User Agent String of Baidu Spider: 

Mozilla/5.0 (compatible; Baiduspider/2.0; +http://www.baidu.com/search/spider.html)

Sogou Spider

Another important crawler for the Chinese market. Sogou is a major search engine in China, and its bot, Sogou Spider, indexes billions of Chinese-language pages. The same logic applies here: if you don’t target China, you may want to block it.

Full User Agent String of Sogou Spider: 

Sogou Pic Spider/3.0( http://www.sogou.com/docs/help/webmasters.htm#07)
Sogou head spider/3.0( http://www.sogou.com/docs/help/webmasters.htm#07)
Sogou web spider/4.0(+http://www.sogou.com/docs/help/webmasters.htm#07)
Sogou Orion spider/3.0( http://www.sogou.com/docs/help/webmasters.htm#07)
Sogou-Test-Spider/4.0 (compatible; MSIE 5.5; Windows 98)

Facebook External Hit

This bot, also known as the Facebook Crawler, activates whenever a link is shared on Facebook, Instagram, or WhatsApp. It quickly crawls the shared URL to pull the title, description, and thumbnail image to generate a preview. If this bot is blocked or the page loads too slowly, the link preview will fail.

Full User Agent String of Facebook External Hit: 

facebot
facebookexternalhit/1.0 (+http://www.facebook.com/externalhit_uatext.php)
facebookexternalhit/1.1 (+http://www.facebook.com/externalhit_uatext.php)

Exabot

This is the crawler for Exalead, a French software company that provides enterprise search platforms. You are less likely to see this bot unless you are in a specific industry that uses its services.

Full User Agent String of Exabot: 

Mozilla/5.0 (compatible; Konqueror/3.5; Linux) KHTML/3.5.5 (like Gecko) (Exabot-Thumbnails)
Mozilla/5.0 (compatible; Exabot/3.0; +http://www.exabot.com/go/robot)

Swiftbot

Swiftbot is different. It is the crawler for Swiftype, a service that provides custom on-site search engines. This bot only crawls the websites of Swiftype’s customers to power their internal search bars. It does not crawl the general web.

Full User Agent String of Swiftbot: 

Mozilla/5.0 (compatible; Swiftbot/1.0; UID/54e1c2ebd3b687d3c8000018; +http://swiftype.com/swiftbot)

Slurp Bot

This is the crawler for Yahoo. While Yahoo Search is now largely powered by Bing, Slurp Bot still crawls pages to support other Yahoo properties like Yahoo News and Yahoo Finance, helping to create a personalized experience for users.

Full User Agent String of Slurp Bot: 

Mozilla/5.0 (compatible; Yahoo! Slurp; http://help.yahoo.com/help/us/ysearch/slurp)

CCBot

Run by the non-profit Common Crawl, CCBot’s mission is to crawl the internet and provide a copy of its data for free to the public. Researchers, developers, and AI companies use this massive dataset for projects. In fact, the GPT-3 language model was trained in part on data from Common Crawl.

Full User Agent String of CCBot: 

CCBot/2.0 (https://commoncrawl.org/faq/)
CCBot/2.0
CCBot/2.0 (http://commoncrawl.org/faq/)

GoogleOther

A newer crawler from Google, launched in 2023. It uses the same technology as the main Googlebot but is used by internal Google teams for research and development. Its creation helps reduce the workload on Googlebot, allowing it to focus on indexing for search results.

Full User Agent String of GoogleOther: 

GoogleOther

Google-InspectionTool

This is another specialized Google crawler. It is used when you use a testing tool within Google Search Console, such as the URL Inspection tool or the Rich Results Test. When you test a live URL, this is the bot that fetches the page on demand.

Full User Agent String of Google-InspectionTool: 

Mozilla/5.0 (Linux; Android 6.0.1; Nexus 5X Build/MMB29P) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/W.X.Y.Z Mobile Safari/537.36 (compatible; Google-InspectionTool/1.0)
Mozilla/5.0 (compatible; Google-InspectionTool/1.0)

The 8 Key Commercial Crawlers for SEO

These crawlers belong to the powerful SEO tools that professionals use to analyze and improve websites. Seeing them in your logs means an SEO professional is likely analyzing your site.

AhrefsBot

The crawler for Ahrefs, an SEO platform known for having one of the world’s largest backlink indexes. It crawls billions of pages daily to discover who links to whom, providing essential data for competitive analysis. It is considered the second most active crawler after Googlebot.

SemrushBot

This bot powers Semrush, a comprehensive SEO toolkit. It collects data for a wide range of features, including site audits, backlink analysis, keyword research, and its content writing assistant.

Rogerbot

The crawler for Moz, one of the original SEO software companies. Rogerbot gathers data for Moz Pro campaigns, specifically for site audits. The information it collects also helps power Moz’s proprietary “Domain Authority” score.

Screaming Frog

This is a popular desktop-based crawler used by technical SEOs. Instead of crawling the whole web, you use Screaming Frog to run a deep crawl of your own site. It’s excellent for finding technical problems like broken links, redirect chains, and duplicate content.

Lumar (formerly DeepCrawl)

Lumar is an enterprise-level crawler designed for large, complex websites. It helps businesses manage their technical health and site architecture, boasting some of the fastest crawling speeds on the market.

Majestic

The crawler for Majestic, another SEO tool that specializes in backlink analysis. It provides unique metrics like “Trust Flow” and “Citation Flow,” which help SEOs evaluate the quality and influence of a site’s backlink profile.

cognitiveSEO

This bot powers the cognitiveSEO platform, which focuses on providing a full set of data and recommendations to improve a site’s ranking. It crawls a site and provides a customized audit with actionable improvement steps.

OnCrawl

An SEO crawler and log analyzer aimed at enterprise clients. OnCrawl provides highly technical insights by combining crawl data with server log file analysis, allowing SEOs to see exactly how bots interact with their site.

Protecting Your Site from Malicious Crawlers

Not all bots are good. Some are designed for harmful purposes and can hurt your website’s performance and security. Understanding how to identify and block these bad bots is just as important as welcoming good ones.

Types of Malicious Bots

• Content Scrapers: These bots steal your content and republish it on other websites. This can lead to duplicate content problems, where search engines may have trouble deciding which version is the original, potentially harming your rankings.
• Spambots: These bots crawl websites looking for email addresses to add to spam lists. They may also fill out contact forms with spammy comments or advertisements, creating a nuisance for you to clean up.
• Aggressive Crawlers: Some bots, even legitimate ones, are poorly configured. They may crawl your site too frequently or too quickly, overwhelming your server. This can slow down your website for real users and even cause it to crash.
• Vulnerability Scanners: These are bots specifically designed to probe your website for security weaknesses, such as outdated software or plugins. Hackers use them to find an entry point to attack your site.

How to Block Malicious Bots

Identifying and blocking bad bots requires more than just a robots.txt file, which they will ignore.

Step 1: Analyze Your Server Logs

The first step is to look at your website’s server logs. Each log entry shows the IP address, user agent (the bot’s name), and the page requested. Look for suspicious patterns, such as a bot that claims to be Googlebot but uses an IP address that doesn’t belong to Google.

Step 2: Block by IP or User Agent

If you identify a malicious bot, you can block it at the server level. This can be done by editing your site’s .htaccess file to deny access to specific IP addresses or user agents. This is a more forceful method than robots.txt.

Step 3: Use a Web Application Firewall (WAF)

The most effective modern solution is to use a WAF from a service like Cloudflare or Sucuri. A WAF sits between your website and the internet, automatically analyzing incoming traffic. It uses sophisticated rules and behavioral analysis to identify and block malicious bots in real time before they can even reach your site.

Web crawlers are the invisible engines that power the search engines we use every day. They are the bridge between your content and your potential customers. By understanding how they work, you can move from being a passive website owner to an active manager of your online presence.

Making sure your site is easy for good bots to crawl while protecting it from bad ones is a fundamental part of a successful digital strategy. By maintaining a clean site structure, using tools like sitemaps and robots.txt correctly, and investing in security, you make it easier for search engines to find, understand, and rank your content. This ensures that all the hard work you put into your website translates into real-world visibility and success.