🤖 Overview

Mr.4x3 is a web crawler operated by Common Crawl, a nonprofit organization that maintains a free, open repository of web crawl data. First documented in 2021, Mr.4x3 is one of several crawlers used by Common Crawl to build its monthly web archives, which are publicly available for research, AI training, and analytics. The bot's name derives from the "4x3" pattern of its user-agent string, indicating a versioned crawl agent.

🌐 Technical Behavior

Mr.4x3 performs broad, systematic crawls of publicly accessible web pages, typically starting from seed lists of popular domains. It fetches pages at a moderate rate to avoid overloading servers. According to Common Crawl's official documentation (https://commoncrawl.org), the crawler respects rate limits and uses a distributed architecture with IP ranges spanning multiple AWS regions, including 54.240.0.0/12 and 52.1.0.0/16. It supports HTTP/1.1 and HTTP/2, and requests both HTML and non-HTML resources like CSS and JavaScript for page rendering analysis, though it does not execute client-side scripts.

📋 robots.txt Compliance

Mr.4x3 fully honors robots.txt directives. Common Crawl's official policy (https://commoncrawl.org/faq) states that their crawlers, including Mr.4x3, check robots.txt before each crawl session and honor Disallow rules. They also provide a mechanism for webmasters to request removal from future crawls via their opt-out form. The bot caches robots.txt for a maximum of 24 hours to reduce server load.

🔍 Detection Indicators

The primary User-Agent string for Mr.4x3 is Mozilla/5.0 (compatible; Mr.4x3/1.0; +https://commoncrawl.org/bot). It may also appear as Mr.4x3/1.0 without the Mozilla prefix. Behavioral fingerprints include sequential request patterns with a consistent crawl delay of 1–2 seconds between requests to the same domain. The bot does not include a Referer header but sends an Accept header of text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8.

📊 Data Usage

All data collected by Mr.4x3 is used to build the Common Crawl dataset, a freely available corpus of billions of web pages. This dataset fuels AI training (e.g., for large language models like BERT and GPT), academic research in natural language processing, web analytics, and digital preservation. The crawled data is stored in WARC files and made available for download via AWS S3 and other mirrors.

⚙️ Rate Limiting Policy

While Mr.4x3 is legitimate and respects robots.txt, its high-volume, multi-threaded crawling can still cause performance issues on smaller or poorly configured web servers. Rate limiting is recommended to protect application resources from excessive requests, especially when the bot revisits sites monthly. Official rate limits are not published, but typical thresholds of 10–20 requests per second are effective.

ⓘ Data Notice: The information presented above has been compiled from publicly available internet sources. Boteraser aggregates this data solely for informational purposes and does not independently classify, evaluate, or endorse any findings about the bots listed. The accuracy and completeness of this information is the sole responsibility of the original publishers. Boteraser and its operators accept no liability for any decisions made based on this data.