Cloudflare Error 521: Meaning & Fix
A 521 Web Server Is Down error message signals that Cloudflare reached the IP address of your origin web server but the web server refused the connection or is offline. While the origin web server downtime must be resolved on the server itself, rotating proxies and well‑timed scraper requests can sidestep Cloudflare IP addresses-based blocks that sometimes appear as 521 errors.
What causes the Cloudflare error 522?
Some of the most common causes of a 521 “Web Server Is Down” error message are the origin web server being offline or refusing connections, or a firewall that blocks a range of Cloudflare IP addresses. Aggressive security or rate‑limit rules (sometimes triggered by rapid scraping from a single IP) can alsao make the web server drop Cloudflare’s handshake, resulting in this error.
How proxies help with the web server down error
Avoid rate limits with rotating proxies
If you’re sending too many requests from a single IP, Cloudflare may flag this activity as suspicious and return a 521 error message page. Rotating proxies help by distributing requests across a pool of IP addresses, reducing the load per IP and lowering the chances of triggering rate limits, automated blocks, and web server down error message
Focus on quality and reliability
Using low-quality or overused IPs can increase the chances of triggering common error codes like 521. Best proxy providers offer ethically-sourced IPs, smart rotation, and geographic flexibility, all of which can help maintain stable connections and reduce the likelihood of Cloudflare blocking your traffic.
Imitate organic user behavior
By using Cloudflare IP addresses from real devices, residential proxies make your scraping traffic look more like that of a genuine user. This helps circumvent Cloudflare's bot detection systems, which are often triggered by unnatural request patterns. Learn more about proxy error codes and how to address such cases on our blog.
All-in-one solution to avoid web server down
Oxylabs’ Web Scraper API is specifically designed to handle most common error message codes like Cloudflare 521 by managing proxy rotation, retries, headers, and everything else for you. Forget about interruptions and extract large volumes of public data from even the most complex targets hassle-free.
ML-driven proxy management
Built-in proxy support with AI features for proxy rotation and evaluation. The system selects proxies that work best for the target and gives the highest success rate with the lowest response time.
Dynamic browser fingerprinting
AI-powered browser fingerprinting and response recognition help you to perform large-scale web scraping operations with almost zero IP blocks and CAPTCHAs.
JavaScript rendering
Oxylabs infrastructure automatically runs headless browsers with custom settings on your behalf to extract public data from web pages that require JS rendering.
Automatic retries
If your web scraping request encounters an issue, Web Scraper API will opt for a different set of client device parameters and resend the HTTP request.
Headless Browser
JavaScript-based page rendering with a single line of code. You can set up custom browser instructions and enable the browser to execute mouse clicks and other web interactions.