If you’ve spent any time browsing the web, you’ve seen it. That cold, unhelpful message staring back at you: 404 – Not Found. It’s the most recognisable error code on the internet, and for good reason [it’s also the most common]. For webmasters and site owners, a 404 isn’t just a minor inconvenience for visitors. Left unchecked, it can quietly erode your search engine rankings, damage user trust, and cost you real traffic over time.
Let’s break down exactly what a 404 is, why it happens, what you can do to prevent it, and why error codes in general are such a nightmare for SEO.
What Is a 404 Error?
A 404 error is an HTTP status code returned by a web server when it cannot find the page being requested. The communication is simple: the browser asked for something, the server understood the request, looked around, and came back empty-handed. The resource doesn’t exist at that address (at least not anymore, or not yet, or never did).
The code itself is part of the 4xx family of HTTP status codes, which are all client-side errors. In other words, the server is telling you the problem originates from the request being made, not from the server itself having a meltdown [that’s the 5xx family’s job].
Why Does It Happen?
404s are almost always caused by one of a handful of situations, and most of them are entirely avoidable.
Moved or deleted pages are the number one culprit. Someone redesigns a site, restructures the URL hierarchy, migrates to a new CMS, or simply deletes old content (and nobody sets up proper redirects). All the old URLs that existed before? Now they’re ghosts pointing to nothing.
Typographical errors in links are a close second. A human typed a URL wrong, either in a menu, a blog post, an email campaign, or an external backlink. One misplaced character is all it takes.
Changed domain structure is another frequent offender. Moving from HTTP to HTTPS, switching from www to non-www, or reorganising category paths can invalidate hundreds of URLs simultaneously if the transition isn’t handled carefully.
Broken external links are outside your direct control but still affect your site’s reputation. Another site links to you, you later change that URL, and now their link leads to a 404 on your end. You’ve lost the referral traffic and potentially the link equity.
Expired or removed content (seasonal promotions, discontinued products, outdated articles) can leave behind dead-end URLs that search engines have already indexed.
The SEO Catastrophe Nobody Talks About Enough
Error codes are a genuine SEO mess, and 404s sit at the top of the pile. Here’s why they hurt so badly.
When search engine crawlers visit your site and repeatedly hit 404s, they interpret those pages as gone. If those pages had accumulated backlinks, social shares, or ranking authority over time, all of that value evaporates. The link equity that those URLs had built up doesn’t automatically transfer somewhere useful (it just dies at the broken endpoint).
Beyond lost equity, crawl budget becomes a real concern for larger sites. Search engines allocate a limited amount of crawl time to any given domain. Every time a crawler wastes a visit on a dead URL, that’s a slot it didn’t use to discover or re-index something valuable. On a site with hundreds of 404s, you’re essentially paying a crawl tax for your own negligence.
Then there’s the user experience dimension, which Google increasingly factors into its ranking signals. If a visitor arrives from a search result and lands on a 404 page, they bounce. That tells Google the result wasn’t satisfying. Do that enough times across enough users, and your rankings for those terms will eventually slide.
Soft 404s are an even sneakier problem. These occur when a server returns a 200 OK status (meaning “everything’s fine”) but the actual page content just says something like “page not found” or is essentially empty. Search engines hate these because they’re deceptive (the server claims success while delivering nothing of value). Google specifically calls these out in Search Console, and they can be just as damaging as hard 404s.
What Webmasters Can Do About It
The good news is that 404s are very much a solvable problem. The key is being proactive rather than reactive.
Set up 301 redirects for every moved or deleted page. A 301 is a permanent redirect that tells search engines and browsers that a resource has moved, and to go to the new location instead. Done correctly, a 301 passes the majority of the original page’s link equity to the destination. If you’re on Apache, this is handled in your .htaccess file. If you’re on Nginx, you’ll configure it in your server block. WordPress users have redirect plugins that make this straightforward. The rule is simple: before you move or delete anything, plan your redirects first.
Audit your site regularly with a crawl tool. Tools like Screaming Frog, Sitebulb, or even Google Search Console’s Coverage report will surface broken internal links and crawl errors. Make this part of your monthly or quarterly maintenance routine, not something you only look at when traffic drops.
Monitor Google Search Console. Search Console will tell you exactly which URLs Google has attempted to crawl and failed. The Pages report under Indexing is your first line of defence. If GSC is flagging 404s, those are the ones that matter most from an SEO perspective [they’re URLs Google knows about and is actively trying to reach].
Create a helpful custom 404 page. Even with the best redirect strategy in the world, some 404s will slip through. When they do, don’t just serve the server’s default blank error screen. A custom 404 page that includes your site’s navigation, a search box, and links to popular or related content can salvage a visit that would otherwise result in an immediate bounce. It won’t fix the SEO problem, but it softens the user experience hit considerably.
Implement a redirect map before any site migration. If you’re relaunching a site, switching platforms, or doing a major URL restructure, build a complete mapping of old URLs to new URLs before anything goes live. This is non-negotiable. A migration without a redirect map is one of the fastest ways to nuke years of accumulated SEO value in a single afternoon.
Fix broken outbound links too. Internal 404s are the priority, but broken outbound links hurt your credibility. Periodically check that the external sites and resources you link to are still live.
A Final Word
The 404 is called the king of errors for a reason (it’s everywhere, it’s persistent, and most webmasters dramatically underestimate how much it costs them over time). Treating error monitoring as an ongoing practice rather than a one-time fix is one of the simplest high-return habits you can build into your site management routine.
If you want to go deeper on how error handling, redirect structures, and technical fundamentals connect to your broader SEO strategy across every major search engine (not just Google0, it’s worth checking out SEO Fundamentals by Stephen Driver from PCGuys. The book covers everything from .htaccess redirect configuration to sitemap structure, robots.txt optimisation, hreflang, Core Web Vitals, and ranking strategies for Bing, Yandex, Baidu, DuckDuckGo, YaCy, Snipesearch, and more. It’s built on over two decades of real-world deployment experience (not recycled blog theory) and is designed to walk you through every critical technical and content SEO checkbox in one systematic sweep. If you’re serious about cleaning up your site’s technical foundation and improving visibility across the full search ecosystem within a realistic timeframe, it’s a solid investment.
