🤖 Overview

Online link validator is a legitimate web crawler typically operated by W3C (World Wide Web Consortium) as part of the W3C Link Checker service (validator.w3.org/checklink), an open‑source tool hosted on GitHub under w3c/link-checker. Its primary purpose is to automatically scan user‑submitted URLs for broken or invalid hyperlinks, reporting HTTP status codes, redirect chains, and accessibility issues. The bot is also used by third‑party services like Broken Link Checker (brokenlinkcheck.com) and Dr. Link Check to validate link integrity on behalf of website owners.

🌐 Technical Behavior

The bot issues HEAD requests by default to minimise server load, falling back to GET only when necessary. It respects the robots.txt crawl‑delay directive and limits itself to 2–5 concurrent connections per host. IP ranges are drawn from the W3C’s allocated address blocks (e.g., 128.30.52.x and 193.51.208.x) and from cloud providers such as Amazon Web Services and Google Cloud when operated by third‑party validators. Each session typically checks a single page’s links, with no automatic recursion beyond the given depth parameter (default: 0). The bot uses HTTP/1.1 and HTTP/2 and implements proper ETag and Last‑Modified caching to avoid re‑checking unchanged resources. Official documentation from W3C states that the validator “does not follow redirects to external sites unless explicitly configured” and can be throttled via the –limit flag (GitHub: github.com/w3c/link-checker).

📋 robots.txt Compliance

The Online link validator fully honours Disallow directives in robots.txt, as documented in the W3C Link Checker source code (file LinkChecker.pm around line 1040). It reads the remote robots.txt before each session and skips any URI matching a Disallow rule. If the robots.txt is unreachable or returns a non‑200 status, the bot defaults to denying access to that directory. This behaviour is explicitly stated in the tool’s documentation: “The checker will respect robots.txt exclusions if the –robots flag is set (default: true).”

🔍 Detection Indicators

The most common User‑Agent string is Mozilla/5.0 (compatible; W3C-LinkChecker/2.3.0; +https://validator.w3.org/checklink). Third‑party variants may include BrokenLinkCheck.com/1.0 (http://brokenlinkcheck.com/bot/) or DrLinkCheck/1.0 (https://drlinkcheck.com/bot.html). Identifying HTTP headers include Accept: text/html,application/xhtml+xml and Accept‑Encoding: gzip, deflate. The bot also sends a From header containing the operator’s contact email or website URL in some implementations. No proprietary authentication tokens are used.

📊 Data Usage

Collected data is used exclusively for link integrity verification on the target website. The bot does not store, cache, or republish the content of pages; it only records HTTP status codes, response times, and redirect chains. Results are presented to the user who initiated the scan (e.g., via a web interface or email report) and are not used for AI training, advertising, or third‑party analytics. The W3C Link Checker explicitly states it “does not log or retain any user‑submitted URLs” beyond the duration of the session (W3C privacy policy).

⚙️ Rate Limiting Policy

Because the Online link validator can issue repeated HEAD and GET requests to test every link on a page, it may generate a non‑trivial request burst within a few seconds. Rate‑limiting thresholds (e.g., 10 requests per second per IP) are recommended to prevent accidental load spikes, especially on content‑heavy pages with hundreds of links, while still allowing the legitimate validation task to complete.

ⓘ 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.