The True Identity of "404"
If you've used the internet, you've surely encountered "404 Not Found" when trying to access a website. You understand the page wasn't found, but why such an odd number as "404"?
In fact, 404 is one of the HTTP status codes. These are 3-digit numbers that web servers use to communicate "the result of a request" to browsers, and the first digit follows a specific pattern.
- 1xx: Processing ("Got it, hold on a moment")
- 2xx: Success (200 OK is the classic. "Everything went well")
- 3xx: Redirect ("It's moved to a different location")
- 4xx: Client error ("There's a problem with your request")
- 5xx: Server error ("Sorry, it's our fault")
404 falls under "4xx = your side's problem," where "04 = not found." In other words, it means "the page at the URL you specified doesn't exist on this server." These status codes are part of the HTTP/HTTPS protocol that governs all web communication.
Is the "CERN Room 404" Legend True?
There's a famous internet urban legend that "404 originated from Room 404 at CERN (the European Organization for Nuclear Research), where the server was located." The story goes that Tim Berners-Lee, the inventor of the Web, worked in Room 404 at CERN, and when a file couldn't be found, the response was "I checked Room 404, but it wasn't there."
However, this is not true. There is no confirmation that a Room 404 ever existed in CERN's buildings, and tracing the story back never leads to a primary source. The number 404 was assigned while the HTTP specification was being drafted: 4xx was set aside as the block for client errors, and each condition was given the next number in that sequence. The meaning of the number lives in the numbering scheme itself, not in any building.
Creative Uses of 404 Pages
Many companies use their 404 pages as an opportunity to entertain users. The best known example is GitHub, whose 404 page still greets visitors with "This is not the web page you are looking for," a nod to "Star Wars," as of August 2026.
There is a catch worth knowing. Stories about "that company's brilliant 404 page" circulate endlessly online, but most of the pages they describe are already gone. Companies rebuild their 404 pages whenever they redesign the site, and because a 404 page appears in neither search results nor sitemaps, there is almost no way to check from the outside whether an older design survives. Open a 404 page featured in an article from a few years ago and you will often land on a plain default design instead. When you come across a story about a memorable 404 page, check which point in time it describes before believing it.
Playfulness is not the main purpose of a 404 page, though. Its real job is to keep users from leaving the site when they hit a dead end, guiding them to the homepage or the search function instead.
Other "Interesting" Status Codes
- 418 I'm a teapot: Defined in RFC 2324 as an April Fools' joke in 1998 for when "a teapot is asked to brew coffee." It's a joke, but it exists as an official RFC
- 451 Unavailable For Legal Reasons: A page that's inaccessible for legal reasons. The number was chosen in reference to Ray Bradbury's novel "Fahrenheit 451" (a dystopian novel about book burning)
- 503 Service Unavailable: The server is temporarily overloaded. Commonly seen when popular ticket sales begin
- 301 Moved Permanently: The page has permanently moved. Accessing the old URL automatically redirects to the new one
How to Reduce 404 Errors
You often hear that "a lot of 404s will drag your rankings down," but that is not accurate. Google states in its official help documentation that a URL which does not exist returning 404 has no effect on the site's search performance and does not harm its indexing or ranking. A 404 is the correct answer to "that page is not here," and it is a normal part of the web.
That does not mean 404s can be left alone. The real damage lies not in rankings but in the users who never reached what they were looking for and simply left, and in the contradiction of your own sitemap or internal links pointing at URLs that return 404. "Soft 404s," where a missing page returns 200 or force-redirects to the homepage, are actually handled worse by search engines, so they are best avoided.
- Set up 301 redirects when pages are deleted or moved
- Regularly check your sitemap and internal links, fixing first the 404s your own site points people to
- Prepare a custom 404 page that guides users to the homepage or search
- Configure proper HTTP security headers to ensure that even error pages are served securely
On IP Check-san as well, accessing a non-existent page displays a custom 404 page with navigation back to the homepage.
Summary
404 was born from the systematic numbering of HTTP status codes and has nothing to do with CERN's Room 404. Next time you encounter a 404 page, take a moment to enjoy whatever creative design that site has prepared.
Related Terms in This Article
Frequently Asked Questions
What does the number 404 mean?
In HTTP status codes, the first digit 4 indicates a client error (the request was wrong), and 04 is the specific error number for 'Not Found.' The numbering follows a systematic scheme, not a room number or other anecdotal origin.
What is 418 I'm a teapot?
HTTP 418 was defined in RFC 2324 as part of an April Fools' joke in 1998, describing the Hyper Text Coffee Pot Control Protocol. A teapot responding to a coffee brewing request returns 418 to indicate it is a teapot, not a coffee pot. Despite being a joke, many web frameworks implement it.
Do 404 errors affect SEO?
Google states in its official help documentation that a URL which does not exist returning 404 has no effect on the site's search performance and does not harm its indexing or ranking. The real damage is not in rankings but in the users who never reached what they were looking for and simply left, and in the contradiction of your own sitemap or internal links pointing at URLs that return 404. Do set up a 301 redirect when a page has moved.