Most websites are visited by far more than just human users. An invisible crowd of crawlers, spiders, and bots constantly travels through web pages, collecting data for search engines, SEO platforms, social media sites, and now generative AI systems.
Understanding who these bots are and how they behave helps developers maintain visibility, monitor performance, and guard their resources.
What Are Web Crawlers
A crawler is a program that automatically visits pages, follows links, and collects data. It can serve different goals: indexing websites for search results, analyzing site performance, training AI models, or checking compliance. Each crawler identifies itself in your server logs with a distinctive user agent name.
Major Search Engine Crawlers
Googlebot
Used by Google Search to index pages across the web. Google runs multiple versions for desktop and mobile, ensuring it captures mobile-first content accurately.
Bingbot
Operated by Microsoft, Bingbot indexes web content for Bing and also powers search features for platforms such as Yahoo and DuckDuckGo in some regions.
YandexBot
Used by Yandex from Russia, this bot scans sites both in local and international domains. It obeys robots.txt rules and focuses on content likely to interest its regional users.
Baidu Spider
Baidu operates the main crawler for the Chinese market. Developers targeting visibility in China often allow it to access localized pages or simplified Chinese versions of their sites.
Social Media Platform Crawlers
Facebook External Hit
Used by Facebook to fetch link previews when URLs are shared. It requests meta tags like og:title, og:description, and og:image.
Twitterbot
Checks page metadata for Twitter Card previews when users post links on X (formerly Twitter).
LinkedIn Bot
Retrieves Open Graph and meta content to display thumbnails and summaries when URLs are shared on LinkedIn posts and messages.
SEO and Marketing Crawlers
AhrefsBot
The active crawler from Ahrefs used for backlink, keyword, and ranking data. It’s one of the most frequent non-search engine visitors many websites see.
SemrushBot
Used by Semrush for competitive analysis and visibility reporting. It gathers structured data, backlinks, and on-page keywords.
Moz’s RogerBot
Responsible for crawling websites to supply Moz’s link and domain authority metrics.
AI and Generative Model Crawlers
GPTBot (OpenAI)
OpenAI’s GPTBot collects publicly available text and code from the internet to train and improve GPT models like ChatGPT. OpenAI provides documentation on how to block or allow it using robots.txt.
Common Crawl
Though not tied to one company, Common Crawl plays a major role in AI development. It creates open datasets of web content that organizations, including AI research groups, use for training large language models.
Anthropic’s ClaudeBot
Anthropic uses this crawler to gather text for research on large language models. Like GPTBot, it follows robots.txt instructions.
PerplexityBot
Used by Perplexity AI to index public sites for real-time question answering and reference search. It collects factual and structured data rather than personal or restricted content.
Applebot for AI
Apple’s crawler now supports data collection for Apple’s private AI models, beyond its earlier role in powering Siri and Spotlight search results.
Security, Monitoring, and Infrastructure Bots
UptimeRobot and StatusCake
These bots continuously check server responsiveness and uptime, often every few minutes. They help alert teams when websites go down.
DuckDuckBot
Used by DuckDuckGo to index the web while respecting user privacy and minimizing tracking.
Cloudflare and Similar Services
These bots appear during cache checks, firewall tests, or CDN diagnostics. They are generally safe and follow tight access rules.
Recognizing and Managing Bots
Each of these crawlers declares a unique user agent string, such as “GPTBot/1.0” or “Googlebot/2.1.” You can view them in your web server logs. To control their access, use a robots.txt file to specify which parts of your site they may visit. For AI bots, you may choose to restrict requests if you do not want your content included in datasets for model training.
Closing Thoughts
The web today is explored as much by machines as by humans. Search engines keep information discoverable. SEO platforms analyze performance. Generative AI crawlers harvest data to make language models smarter. Recognizing which bots interact with your website empowers you to manage your presence, bandwidth, and privacy effectively.
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