---
title: "521 Web Server Is Down"
canonical: "https://lemwatch.com/http-status-codes/521"
category: "server-error"
last_verified: "2026-08-11"
source: "https://lemwatch.com"
---

# HTTP 521 Web Server Is Down

**Summary** — The origin web server has refused or is not responding to Cloudflare's connection.

## What it means

HTTP 521 is a Cloudflare-specific error code indicating that the origin web server refused the connection from Cloudflare. This means Cloudflare can't reach your server at all.

## Common causes

- Origin server is completely down
- Origin firewall blocking Cloudflare IPs
- Origin server crashed
- Port not open on origin server

## How to fix

- Check if your origin server is running
- Whitelist Cloudflare IP ranges in your firewall
- Verify the correct origin IP in Cloudflare settings
- Check that your web server is listening on the correct port

## SEO impact

Critical. Your entire site is unreachable through Cloudflare. Search engines will see an error page.

## Monitoring tip

LemWatch monitors through CDN layers like Cloudflare and can distinguish between CDN errors and origin server issues.

**Related:** [502](https://lemwatch.com/http-status-codes/502.md), [523](https://lemwatch.com/http-status-codes/523.md), [524](https://lemwatch.com/http-status-codes/524.md)

_Canonical HTML page: https://lemwatch.com/http-status-codes/521_