Tips and Tricks to Deal with Cloudflare Error 520

You’re running a script, scraping a website, or just browsing—and suddenly, Error 520 appears. No explanation. No hint. Just a wall in your workflow. Frustrating? Absolutely. Confusing? Even more so. But once you understand what’s really happening, you can tackle it—and sometimes even prevent it—from happening again.

The Definition of Error Code 520

Every web request is a conversation between your browser (or automation tool) and a server. Most of the time, it’s seamless. But when the origin server responds in a way Cloudflare can’t understand, you get 520.
It’s essentially a shrug from the server: “I received your request, but I can’t tell you what went wrong.”
Unlike standard HTTP 5xx errors, 520 is unique to Cloudflare. You won’t find it in the official IANA list. It’s often confused with:

• 521: Connection couldn’t be established.
• 524: Server timed out.
• 520: Server responded, but the response was invalid, empty, or unexpected.

Why Does Error 520 Occur

The culprit is usually the origin server. Common triggers include:

• Crashed or misconfigured server.
• Firewalls or security plugins blocking Cloudflare IPs.
• Headers or cookies exceeding Cloudflare limits (16 KB individually, 32 KB collectively).
• Malformed or empty responses without proper HTTP codes.
• Incorrect HTTP/2 setup.
• TCP timeouts too short, causing Cloudflare to treat responses as empty.

From a user perspective, it all looks the same: a 520 error screen. Yet oddly, some pages might work while others fail. Logging in, submitting a form, or loading a dynamic component could trigger it.

Simple Fixes That Work

Some 520 errors require server access—but you can often troubleshoot as a user or developer first:

• Retry the connection. Refresh your browser or script. Servers sometimes just need a moment.
• Clear cookies. Oversized request headers can trigger 520. Incognito mode or programmatic cookie management helps.
• Avoid blacklisted IPs. Using proxies? Rotate IP addresses, tweak browser fingerprints, and disable conflicting tools.

If these fail, server-side fixes are next:

• Temporarily set Cloudflare DNS to “DNS only” to bypass the CDN.
• Check server logs for crashes or anomalies.
• Whitelist all Cloudflare IPs in firewall rules.
• Ensure HTTP/2 is properly configured.
• Trim headers to fall within Cloudflare’s limits.

When none of these work, contact your hosting provider with logs, affected IPs, and the Cloudflare Ray ID.

Stopping 520 Errors Automatically

Automation makes error 520 more visible. But you can mitigate downtime with preemptive strategies. Implement rate limiting and automatic retries in your scripts. Here’s an example using Python’s requests library:

import time
import requests

urls = ['https://example.com/page1', 'https://example.com/page2']
max_retries = 3
retry_delay = 10
rate_limit_delay = 5

for url in urls:
    success = False
    for attempt in range(max_retries):
        try:
            response = requests.get(url)
            print(f"{url}: {response.status_code}")
            if 200 <= response.status_code < 300:
                success = True
                break
            else:
                print(f"HTTP error {response.status_code} for {url}")
        except requests.RequestException as e:
            print(f"Attempt {attempt+1} failed: {e}")
        if attempt < max_retries - 1:
            print(f"Retrying in {retry_delay} seconds...")
            time.sleep(retry_delay)
    if not success:
        print(f"All retries failed for {url}")
    time.sleep(rate_limit_delay)

Other tips for administrators:

• Keep server software updated.
• Monitor resource usage.
• Regularly check firewall rules and Cloudflare IP whitelists.
• Ensure DNS records are consistent.
• Increase timeout values to prevent empty responses.
• Manage header and cookie sizes.

Conclusion

Error 520 is frustrating because it’s vague and unpredictable. But knowledge is power. Users can retry, manage cookies, or rotate IPs. Administrators can maintain servers, monitor traffic, and preemptively configure settings.