linkcheck scanner

Scanner User-Agent: linkcheck-scanner

🤖 Overview

linkcheck scanner is an automated legitimate agent commonly associated with open‑source link validation tools such as LinkChecker (maintained at https://linkchecker.github.io/linkchecker/) and commercial services like LinkCheck.com. Its primary purpose is to systematically crawl web pages, follow every hyperlink (both internal and external), and report broken, redirected, or malformed URLs. The results feed into website maintenance dashboards, SEO auditing platforms, and quality‑assurance pipelines used by web developers and content managers.

🌐 Technical Behavior

The linkcheck scanner typically initiates a crawl by requesting a starting URL and then recursively parsing all <a>, <img>, <script>, and <link> elements. It respects HTTP redirects (301, 302) and checks both HTTP and HTTPS variants of each link. Request frequency is configurable by the operator, but common implementations (e.g., LinkChecker v10.4.0) send requests with a default delay of 1–3 seconds between successive fetches. The agent uses HTTP/1.1 with persistent connections and often includes a Accept-Encoding: gzip header. IP ranges vary widely because the tool is run from arbitrary client machines or from cloud instances (AWS, Azure, etc.), so no fixed IP block can be listed.

📋 robots.txt Compliance

The linkcheck scanner generally honors robots.txt directives. The official LinkChecker documentation explicitly states that it checks robots.txt before crawling a domain (see official man page). However, some standalone scanner scripts may bypass this by default unless configured otherwise, so administrators should explicitly test compliance in their own environment.

🔍 Detection Indicators

The most reliable detection indicator is the User-Agent string. The open‑source LinkChecker sends: LinkChecker/10.4.0 (version varies; earlier versions used LinkChecker/9.3). Commercial versions may use Mozilla/5.0 (compatible; LinkCheckScanner/2.0; +https://linkcheck.com/bot). Other fingerprints include a Referer header that always matches the page where the link was found, and an absence of cookies or JavaScript support. Some implementations also send a Via header indicating the proxy used.

📊 Data Usage

Collected data is used exclusively for link integrity verification and SEO health monitoring. No personal or content data is stored—only HTTP status codes, response times, redirect chains, and failure reasons are recorded. Results are aggregated into reports for website owners, with no AI training or search indexing involved. The tool’s output is typically a list of broken links sorted by severity.

⚙️ Rate Limiting Policy

Because the linkcheck scanner can generate a high volume of requests in a short time (especially when auditing large sites), it is rate‑limited to protect server stability. A threshold of 10 requests per second from a single IP is reasonable; exceeding that may indicate a misconfigured or aggressive instance. Blocking is not necessary, but throttling prevents accidental DoS while still allowing legitimate link audits.

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