404 Not Found Error: What It Means and How to Fix It

A 404 Not Found error is the most common HTTP error on the web. Every site will generate them at some point — whether from a deleted page, a typo in a URL, or a broken link from another website. A handful of 404s won't hurt you. But a large number of them, especially on pages that used to rank or receive traffic, can quietly erode your SEO and frustrate your visitors.

Here's what causes 404 errors, how to find and fix them, and how to prevent them from damaging your site.

What Does a 404 Not Found Mean?

A 404 status code means the server is reachable and understood the request, but the resource at that URL doesn't exist. The server simply has nothing to serve at that path.

This is different from a 500 Internal Server Error, where the server itself is broken. With a 404, the server is working fine — it just can't find what was requested.

A 404 can appear because:

• The page was deleted or moved without a redirect.
• The URL was typed incorrectly by the visitor.
• An external site links to a URL that never existed or has since changed.
• A CMS or deployment process changed the URL structure.

Common Causes of a 404 Error

1. The Page Was Deleted or Moved

The most common cause. Someone removed a page, renamed a slug, or migrated content to a new URL structure without setting up 301 redirects. Any existing links — from Google, from other websites, from your own internal navigation — now point to nothing.

2. Typo in the URL

A visitor types yoursite.com/abuot instead of yoursite.com/about. Or a developer hardcodes a link with a missing character. The server looks for the path, finds nothing, and returns 404.

3. Broken Internal Links

Your own site links to a page that no longer exists. This commonly happens after a site redesign, a CMS migration, or when content is reorganised. Internal 404s are especially damaging because they signal poor site maintenance to search engines.

4. Incorrect Server or Rewrite Configuration

If your server isn't configured to route requests properly, valid URLs can return 404s. This is especially common with single-page applications (SPAs) or frameworks that rely on URL rewriting.

For example, a Nginx server hosting a Vue or React app needs a fallback rule:

location / {
    try_files $uri $uri/ /index.html;
}

Without this, refreshing any page other than the root will return a 404.

5. Broken Permalinks After a CMS Update

WordPress and other CMS platforms can break their permalink structure after an update or plugin conflict. Posts that worked yesterday suddenly return 404s across the entire site.

# In WordPress, try flushing permalinks:
# Go to Settings > Permalinks and click "Save Changes"
# Or regenerate .htaccess manually:
sudo cat /var/www/html/.htaccess

6. Case Sensitivity Issues

Linux servers treat URLs as case-sensitive. /About-Us and /about-us are two different paths. If a link uses the wrong case, the server returns a 404 even though the page exists at a slightly different URL.

How to Fix a 404 Not Found Error

Step 1: Find Your 404s

You can't fix what you can't see. Use Google Search Console to find pages returning 404 that Google has tried to crawl:

• Go to Indexing > Pages and filter by "Not found (404)".

You can also check your server logs directly:

# Find 404 responses in Nginx access logs
grep ' 404 ' /var/log/nginx/access.log | awk '{print $7}' | sort | uniq -c | sort -rn | head -20

This gives you the 20 most-requested URLs that returned 404s.

Step 2: Set Up 301 Redirects

For pages that were moved or renamed, add permanent redirects so the old URL points to the new one.

On Nginx:

server {
    # Single redirect
    location = /old-page/ {
        return 301 /new-page/;
    }

    # Redirect an entire directory
    location /old-blog/ {
        rewrite ^/old-blog/(.*)$ /blog/$1 permanent;
    }
}

On Apache (.htaccess):

Redirect 301 /old-page/ /new-page/
RedirectMatch 301 ^/old-blog/(.*)$ /blog/$1

Step 3: Fix Internal Links

Crawl your own site and update any links that point to pages returning 404. Tools like Screaming Frog or a simple crawl script can find these:

# Quick check for broken links using curl
curl -o /dev/null -s -w "%{http_code}" https://yoursite.com/some-page/

Step 4: Create a Custom 404 Page

A well-designed 404 page helps visitors find what they were looking for rather than bouncing. Include a search bar, links to popular pages, and a clear message that the page wasn't found.

Step 5: Fix Permalink or Rewrite Issues

If your entire site is returning 404s, the problem is almost certainly in your server configuration. Check your rewrite rules, verify your document root is correct, and restart your web server:

# Test Nginx configuration
sudo nginx -t

# Reload Nginx
sudo systemctl reload nginx

# Test Apache configuration
sudo apachectl configtest

# Reload Apache
sudo systemctl reload apache2

404 vs 410: Which Should You Use?

A 410 Gone tells search engines the resource was permanently removed on purpose. A 404 simply says it wasn't found. If you've intentionally deleted a page and want Google to de-index it faster, use a 410. If the page moved, use a 301 redirect instead of either.

How Domain Monitor Can Help

A single broken page might not seem urgent, but when critical landing pages or product pages start returning 404s, you lose traffic and revenue without realising it. If a deployment accidentally breaks your URL routing and your entire site starts throwing 404 errors, you need to know immediately — not when customers start complaining.

Domain Monitor checks your site every minute from multiple locations around the world. If your monitored URLs start returning 404 status codes (or any non-2xx response), you'll get an alert within seconds via email, SMS, or Slack. You can set up downtime alerts for your most important pages so you catch routing issues, broken deployments, or accidental deletions before they affect your SEO or your users. Combined with proper website monitoring, you can track not just whether your homepage is up, but whether your key pages are actually serving the right content.

Quick Summary

A 404 here and there is normal. But a growing number of them is a signal that something needs attention — whether it's a missing redirect, a broken deployment, or a misconfigured server.

Related Articles

• 403 Forbidden Error - What It Means and How to Fix It
• 500 Internal Server Error - Causes and How to Fix It
• Most Common Website HTTP Error Codes
• 410 Gone - What It Means and How to Fix It