What is a 404 error and why do pages go missing?

A 404 error means the server can't find the page you asked for. The server is working. It just has nothing at that web address.¹

The full name is "404 Not Found". It's a status code, a number the server sends back with every reply. Browsers turn it into a page that says something like "page not found", but the wording changes from site to site.¹

What a 404 does and doesn't tell you

It says the page is missing. It doesn't say whether it's gone for good or just out of action for now.¹

That's the catch. A 404 is a shrug from the server, not a promise. The page might return tomorrow, or never.¹ There's a more exact code for pages that are gone for good, and the status codes page covers it.

Why pages go missing

Two causes turn up again and again: mistyped addresses, and pages that were moved or deleted with no redirect left behind.¹

Wikipedia lists more, and a few are worth knowing:

• A site gets restructured, so old addresses stop working.²
• Someone deletes the page or its content.²
• A domain name's registration runs out.²
• Someone copies a link wrong into an email, a post or a document.

A link that leads to a 404 is called a broken link, or a dead link. Over time more of them build up, which is known as link rot.²

It's bigger than most people expect. Wikipedia reports that Pew Research found 38% of pages from 2013 had gone missing by 2023.²

If you're the visitor

You can't fix the site, but you can often still find what you wanted.

• Check the address bar for typos, especially if you typed it yourself.
• Cut the address back to the main site name and look around from the home page.
• Use the site's search box, if it has one.
• Search for the page title on a search engine.

Still nothing? The page has probably been removed, and only the site owner can say why.

If you're the site owner

Don't panic over every 404. Google's own help says a 404 isn't necessarily a problem if you removed a page and have nothing to replace it.³

But if the page has moved, send people to the new one. Google says to use a 301 redirect to the new location.³ The page on 301 vs 302 redirects explains what that means and when to use it.

Search engines care too. Google doesn't index addresses that return a 4xx code, and it drops ones that it had already indexed.⁴ So a page that quietly turns into a 404 stops showing up in search.

Your next steps depend on how many dead links you've got:

1. Find them. Checking your own site shows you how.
2. Decide what to do with each one. The repair options are edit, redirect or remove.
3. Make your error page useful for the people who still land on it, using this page-building guide. MDN says custom page design is a good thing in moderation.¹