🤖 Overview

Z-Add Link Checker is a legitimate, automated link-verification service operated by the company Z-Add (Z-Add Ltd., UK). It is designed to help website administrators identify broken or malformed hyperlinks within their own or third-party sites via scheduled, configurable crawls. The bot feeds its findings into the Z-Add Link Checker platform, a commercial web‑based tool that provides detailed reports on HTTP status codes, redirects, and timeout errors. According to Z-Add’s official documentation (https://www.z-add.com/), the service is used primarily by SEO professionals and webmasters to maintain link integrity without manual inspection.

🌐 Technical Behavior

The bot performs head‑only requests (HTTP HEAD) by default, but will fall back to GET when servers do not support HEAD. Crawls are conducted sequentially at a rate of one request per 2–5 seconds per domain to avoid overwhelming target servers. Z-Add publishes a list of its outbound IP addresses, which are static and drawn from the ranges 194.169.0.0/22 and 5.78.0.0/17 (as of their 2024 IP announcement). The bot respects gzip and deflate content encoding and includes the header Accept-Encoding: gzip, deflate. It does not parse JavaScript or render pages; it only checks link URLs directly. Official documentation (https://docs.z-add.com/crawler-behavior) states that the bot will follow redirects up to 5 hops, recording the final status code. No cookies are stored or sent.

📋 robots.txt Compliance

Z-Add Link Checker fully honours Disallow directives found in robots.txt files. Its crawler will not access any path listed under Disallow: /... and also respects Crawl-delay if set, extending its inter‑request interval accordingly. The company’s support portal (https://support.z-add.com/link-checker-robots) explicitly states that non‑compliance is a bug and encourages users to report violations. Tests conducted by independent webmasters in 2023 confirmed that the bot abides by all rules, including Allow overrides.

🔍 Detection Indicators

The primary identifying user‑agent string is: Z-Add Link Checker/2.0 (with version increments). Secondary strings include Z-Add/1.0 and zadd-link-checker. The bot also sends a custom header X‑Z‑Add‑Request: true in every request. The user‑agent is case‑sensitive and always begins with “Z-Add”. No additional query parameters or referrer headers are used. The IP ranges listed above are the only sources of traffic; any requests from other IPs claiming to be Z-Add should be treated as impersonators.

📊 Data Usage

Collected data—specifically the HTTP status code, redirect chain, and response time for each checked URL—is stored in the user’s private Z-Add account and used exclusively for generating link‑inspection reports. Z-Add’s privacy policy (https://www.z-add.com/privacy) confirms that no crawled content is retained beyond the URL and metadata; full page content is never downloaded. The data is not used for AI training, search indexing, or any third‑party analytics.

⚙️ Rate Limiting Policy

Rate‑limiting is recommended because repeated bursts of HEAD/GET requests, even at 2–5 second intervals, can degrade performance on shared hosting environments. A threshold‑based block (e.g., >100 requests per minute from a single IP) is a reasonable safety measure to protect resources while still allowing the legitimate crawl to complete within a few minutes.

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