🤖 Overview

wacbot is the primary web crawler operated by the Internet Archive, a non-profit digital library headquartered in San Francisco, California. Its purpose is to systematically discover, fetch, and preserve publicly accessible web pages for inclusion in the Wayback Machine, the Archive’s permanent digital repository of web snapshots. First documented in 2011, wacbot accounts for the majority of the Internet Archive’s automated crawl traffic, which today archives over 1 billion URLs per month.

🌐 Technical Behavior

wacbot employs a distributed crawl architecture using a fleet of servers hosted within the Internet Archive’s own ASN (AS7941). Its IP range primarily falls within 207.241.224.0/20 and 208.70.28.0/24, though some crawls originate from dynamically assigned addresses. The bot sends HTTP GET requests with a default User-Agent of Mozilla/5.0 (compatible; wacbot/1.0; +https://archive.org/details/wacbot) and respects the Accept-Encoding: gzip, deflate header. It fetches pages sequentially without parallel connections by default, but may increase concurrency under explicit per-domain agreement. The bot observes a Crawl-Delay directive in robots.txt and will wait the specified number of seconds between requests. It requests robots.txt before each crawl session and caches the result for up to 24 hours.

📋 robots.txt Compliance

The Internet Archive publicly states that wacbot fully honors the Robots Exclusion Protocol. It checks the robots.txt file at the root of each domain and obeys all Disallow directives, including those with wildcards. Additionally, the bot supports the X-Robots-Tag HTTP header for per-page exclusion. Evidence from the Archive’s official documentation (https://archive.org/about/robots.txt) confirms that wacbot will cease crawling any path explicitly forbidden.

🔍 Detection Indicators

The most reliable detection method is the User-Agent string Mozilla/5.0 (compatible; wacbot/1.0; +https://archive.org/details/wacbot). Some older crawl jobs may use Mozilla/5.0 (compatible; archive.org_bot +http://www.archive.org/details/archive.org_bot) but wacbot is the modern standard. The bot’s requests always include the header From: [email protected] (or a generic contact email) and set Referer to the root URL of the site being crawled. Behavioral fingerprints include a consistent tcp timestamp offset and a minimum request interval governed by the crawl delay.

📊 Data Usage

All content retrieved by wacbot is stored as WARC (Web ARChive) files in the Internet Archive’s petabyte-scale storage system. These snapshots are made publicly accessible via the Wayback Machine interface at archive.org/web/. The data is used exclusively for preservation, historical research, and public access—the Archive does not sell crawled data, nor does it use it for AI training or advertising analytics. The Internet Archive’s mission is “universal access to all knowledge.”

⚙️ Rate Limiting Policy

wacbot is rate-limited because its crawling can generate thousands of simultaneous requests across a large distributed network, potentially overwhelming smaller websites. Administrators are encouraged to set a Crawl-Delay value in robots.txt (e.g., Crawl-Delay: 10) to enforce a pause between requests. Threshold-based blocking is justified to prevent resource exhaustion while preserving the bot’s legitimate archival function.

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