A 404 error means a page cannot be found on a website. It happens when a browser or search engine tries to access a URL that does not exist or is no longer available.
You may also see it called a 404 not found error. In simple terms, the server is working, but the page being requested is missing.
Why a 404 Error Matters When You SEO Check a Website
When you SEO check a website, 404 errors are one of the most important technical issues to review. They can create a poor user experience, waste crawl budget, and break internal linking paths that help search engines understand your site.
A few 404 errors on a website are normal, especially on older sites or after content changes. The problem starts when important pages, linked pages, or previously indexed URLs return 404 errors without a good reason or without being redirected properly.
What Causes a 404 Error?
A 404 error can happen for several reasons:
- A page was deleted but no redirect was added
- A URL was changed without updating internal links
- A backlink points to an incorrect or outdated page
- A user entered the wrong URL manually
- A migration or site update removed pages by mistake
- The page slug was changed and the old version still gets requests
How 404 Errors Affect SEO
404 errors do not automatically damage a website, but they can become a problem if they affect important pages or appear at scale. When you SEO check a website, 404 errors often reveal weak site maintenance or missed technical fixes.
- Users may land on dead pages instead of useful content
- Search engines may waste time crawling missing URLs
- Broken internal links reduce site quality and navigation flow
- Backlinks pointing to 404 pages may lose their full value
- Important pages can drop out of the user journey entirely
Common 404 Error Problems Found in an SEO Check
When running an SEO check on a website, some 404 issues matter much more than others.
Broken Internal Links
If your own pages link to URLs that return 404 errors, both users and search engines hit dead ends. This is one of the clearest technical issues to fix.
Deleted Pages With No Redirect
If an old page had traffic, rankings, or backlinks, removing it without a redirect can waste valuable SEO signals.
404 Errors on Important Pages
A missing blog post is less serious than a missing service page, category page, or landing page that should still be live.
Backlinks Pointing to Missing URLs
If external sites link to a page that now returns a 404 error, you may be losing authority and referral traffic that could have been preserved with a redirect.
Sitewide Patterns of Missing Pages
If many URLs return 404 errors after a migration, redesign, or CMS update, it can point to a larger technical issue.
404 Error vs Soft 404
A 404 error means the server clearly says the page does not exist.
A soft 404 happens when a page looks like an error page or has no real content, but still returns a normal success status instead of an actual 404 response.
When you SEO check a website, both can be worth reviewing because both can waste crawl activity and create weak user experiences.
How to Check for 404 Errors on a Website
If you want to SEO check a website properly, look for missing URLs in the site’s technical audit and crawl data.
- Find internal links pointing to 404 pages
- Check whether important deleted pages should be redirected
- Review backlinks going to missing URLs
- Look for 404 spikes after migrations or URL changes
- Check whether missing pages should return a 404, a 410, or a redirect
A website SEO checker can help find 404 pages quickly and show which ones are linked internally or still receiving authority signals.
How to Fix 404 Errors
The right fix depends on the situation. If the page has a relevant replacement, add a 301 redirect. If the URL should still exist, restore the page. If the error comes from a broken internal link, update the link to the correct destination. If the page is intentionally gone and has no replacement, leaving it as a true 404 may be acceptable.
Best Practices for Handling 404 Errors
Review 404 errors regularly as part of your technical SEO process. Fix broken internal links quickly, redirect valuable old URLs where appropriate, and make sure your custom 404 page helps users find their next step instead of leaving the site entirely.
Final Thoughts
A 404 error means a requested page cannot be found. It is a common issue, but it becomes important when it affects internal links, high-value pages, or URLs with backlinks. When you SEO check a website, reviewing 404 errors helps you spot broken paths, preserve link value, and improve both technical health and user experience.