What is a 404 error?
A 404 error is the HTTP status 404 Not Found, returned when a server cannot find anything at the requested URL. Visitors usually see a "page not found" page; crawlers see the status code and learn that the URL has no content.
404s are a normal part of the web. Google has said repeatedly that they do not hurt a site's overall rankings. The URL itself drops out of the index, which is the correct outcome for a page that is really gone. The cost comes from what points at it: internal links that send people into dead ends, and backlinks whose value is wasted because the target no longer exists.
How it works
When Googlebot hits a 404, it removes the URL from the index after a few recrawls and gradually checks it less often, but may come back occasionally in case it returns. A 410 Gone status says the removal is deliberate and permanent; Google may drop 410s slightly faster, but in practice treats the two very similarly.
The status code is what counts, not the page design. A custom 404 page must still send a 404 status. If it returns 200 OK, search engines see a thin "page not found" page as real content, which is a soft 404.
For each 404, decide: if a relevant replacement exists, add a 301 redirect; if the content is gone for good and nothing replaces it, let it return 404 or 410; if it is a typo in your own link, fix the link.
Example
Checking the status:
$ curl -I https://example.com/old-guide/
HTTP/2 404
A useful 404 page tells the visitor the page is missing, offers a search box, and links to popular sections. It does not automatically redirect to the home page, which confuses visitors and is treated by Google as a soft 404 anyway.
In WordPress
WordPress serves the theme's 404.php template with a correct 404 status. Renamed slugs, deleted posts, and permalink changes are the main sources. Hydrogen SEO does not log 404 hits, so find them in Search Console's Pages report, the plugin's site audit (broken internal links), and server logs, then add 301s in the Redirection Manager. Hydrogen SEO sets the 404 page to noindex, follow automatically. The full workflow is in find and fix 404 errors and 301 vs 404.
Common mistakes
- Redirecting every 404 to the home page.
- Custom 404 pages that return 200.
- Ignoring 404s that have backlinks, which are the ones worth redirecting.
- Leaving broken internal links in menus and old posts.
Common questions
Do 404 errors hurt SEO?
Not the site as a whole. They matter when important pages break, when internal links lead to them, or when backlinks point at them and their value is lost.
Should I redirect all 404s?
No. Redirect only when a relevant replacement exists. A 404 or 410 is the honest response for content that is gone.