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Why am I seeing 504 or 403 errors in my Prerender.io render history?

Whitelist Prerender.io's IP ranges and user agents in your firewall so AI crawlers receive fully rendered pages.

TL;DR

504 (Gateway Timeout) and 403 (Forbidden) errors in your CDN Analytics or Prerender.io render history almost always mean your firewall is blocking or rate-limiting Prerender.io's requests. Whitelist Prerender.io's IP ranges and user agents in your firewall to fix it. Most setups take 15 to 30 minutes once you have firewall access.

 

Why this Matters

When your firewall blocks or rate-limits Prerender.io's requests, AI crawlers and search engines do not receive the fully rendered version of your pages. Instead they may receive a partial page, an unrendered JavaScript shell, or an error response. Your content may not be indexed accurately, and AI citations and search rankings can suffer.

ℹ️ Not sure which firewall layer is doing the blocking, or how to add a whitelist rule in your specific stack? Ask Nexus, your AI integration assistant, inside your Prerender.io dashboard. Describe your firewall or CDN setup and Nexus will walk you through the right place to add the rules.

How to confirm a firewall block is the cause

Before changing firewall rules, confirm the symptom matches:

  • Open your Prerender.io dashboard and go to Render History or CDN Analytics.
  • Look for repeated 504 or 403 status codes on render attempts.
  • Cross-check whether the affected URLs work normally in your browser. If your browser loads the page fine but Prerender.io is hitting 504 or 403, the issue is almost always firewall-related.

If you see other status codes (200 but partial content, or 5xx from your origin), the cause is different. See What should I do if my pages are not being cached properly? instead.

Step 1: whitelist Prerender.io's IP ranges in your firewall.

Add Prerender.io's full IP range list to your firewall's allow list, so requests from Prerender.io are not blocked or rate-limited.

The current list is published at https://ipranges.prerender.io/ipranges-all.txt. The list is updated as Prerender.io's infrastructure changes, so import it programmatically if your firewall supports it, or schedule a periodic re-import if it does not.

⚠️ Rate-limiting and DDoS-protection rules are the most common cause of 504s, even when no hard block is configured. If your firewall has volume-based limits, exempt Prerender.io's IP ranges from those rules too, not just from the block list. A typical render workload can look like a burst of traffic from a small set of IPs, which is exactly what generic DDoS protection targets.

How you do this depends on your firewall or CDN. Cloudflare, AWS WAF, Akamai, Imperva, and similar products all expose an allow list, but the exact menu names differ. If you are not sure where the allow list lives, check your firewall's documentation or ask your IT or DevOps team.

 

Step 2: whitelist Prerender.io's user agents in your firewall.

Some firewalls block requests by user agent as well as by IP. Add Prerender.io's user agents to the allow list so requests are not rejected by bot-detection rules.

The current list of supported user agents is at Prerender.io crawlers. Match exactly, including casing.

If your firewall has a "known bot" category, check whether Prerender.io's user agents are classified as "good bot" or "unknown bot" and adjust if needed. Some products default to blocking anything that is not on their built-in known-bot list.

 

Step 3: verify your integration is working.

After saving the firewall changes, give them a few minutes to propagate, then re-check your render history.

→ See Verify your Prerender.io integration for the full verification procedure.

✅ Your firewall is correctly configured when new entries in your render history return 200 status codes within 2 to 5 minutes of crawler requests, and the 504 or 403 entries stop appearing for the affected URLs.

If 504 or 403 errors persist after both whitelists are in place, the rules may be applied at a different firewall layer than the one you updated. Common gotchas: a separate WAF in front of your CDN, a regional load balancer with its own access rules, or an origin-server firewall that the CDN passes through to.

 

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💬 Still need help? If 504 or 403 errors persist after whitelisting Prerender.io's IP ranges and user agents, our support team can help.

When you contact us, please include:

  • The affected URLs.
  • Screenshots or logs of the 504 or 403 errors from your render history.
  • Your firewall or CDN provider (Cloudflare, AWS WAF, Akamai, etc.).
  • The whitelist rules you have already applied.

→ Contact us at support@prerender.io

 

 

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