http.app
Zero Data Retention

HTTP 404 NOT FOUND

Nothing at this URL, or the server will not say whether there is. 404 belongs to the 4xx client error class and is defined in RFC 9110.

Zero retention: your headers never leave this browser. Verify it yourself in DevTools.

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About HTTP 404

What Does HTTP 404 Not Found Mean?

Nothing at this URL, or the server will not say whether there is. The code is registered with IANA and defined in RFC 9110.

Client error: the request has a problem, so it cannot be fulfilled as sent. Every code from 400 to 499 shares that general meaning, so a client that does not recognise 404 must treat it like 400.

When Do You See a 404 Response?

404 Not Found means the server has nothing at that URL, or will not admit that it does. Typical causes are typos, deleted pages, renamed routes, broken links from other sites, missing files after a deploy, and case-sensitive paths. Single-page applications often get 404s on refresh when the server is not configured to fall back to index.html. Search engines drop 404 URLs from their index over time, which is usually what you want for dead pages.

How Do You Fix a 404?

Check the exact URL, including case and trailing slash. If content moved, add a 301 or 308 from the old URL rather than leaving a 404. Serve a helpful error page that still returns status 404, not 200, to avoid soft 404s in search results. For content that is gone for good, 410 states that more strongly. A 404 is cacheable by default, so add Cache-Control if it may change soon.

What Does a 404 Response Look Like?

HTTP/1.1 404 Not Found
Content-Type: text/html; charset=utf-8
Cache-Control: max-age=60

404 is cacheable by default under RFC 9110: a browser or CDN may store it and reuse it even without explicit freshness headers, using a heuristic lifetime. Send Cache-Control to say exactly how long.

To inspect a real one without sending it anywhere:

  1. Copy the response headers from your browser Network tab, or from curl -i.
  2. Paste them into the Header decoder to see every header explained.
  3. Check caching in the Cache lane.

Which Status Codes Are Related to 404?

  • 410 Gone: Removed on purpose and not coming back. Search engines drop it faster than a 404.
  • 301 Moved Permanently: The resource has a new permanent URL. Search engines move ranking to it. Clients may change POST to GET.
  • 403 Forbidden: The server knows who you are and refuses anyway. Logging in again will not help.
  • 405 Method Not Allowed: The URL exists but not for this method. Must send an Allow header.

Browse every code on the HTTP status codes page.

What Other Lanes Are in the Reference Section?

  • HTTP status codes: Every IANA-registered status code, with a page per code.
  • MIME types: File extensions to Content-Type, searchable both ways, plus a Content-Type parser.
  • HTTP methods: GET, POST, PUT, PATCH, DELETE and the rest: safe, idempotent, cacheable.

Elsewhere in 2http: Header decoder, Cookie decoder, Cache-Control decoder, CORS checker, User-agent parser, and all eleven lanes on the 2http home page. Part of the 2suite.io privacy-first ecosystem.

Frequently Asked Questions

What is a soft 404?

A page that tells visitors nothing was found but returns status 200. Search engines flag these as errors because the status contradicts the content. Return a real 404 instead.

Should deleted pages return 404 or 410?

Both are fine. 410 signals the removal is intentional and permanent, and search engines may drop the URL slightly faster. 404 is the safer choice when unsure.

Is HTTP 404 an error?

Yes. 404 is a client error response: the problem is in the request, so repeating it unchanged will usually fail again.

Is a 404 response cacheable by default?

Yes. RFC 9110 lists 404 as heuristically cacheable, so caches may store it without explicit headers. Use Cache-Control to control how long.

How Can You Verify That Nothing Leaves This Browser?

You do not have to take our word that your headers stay here. Developer tools show every request a page makes, so you can watch this page work and confirm that nothing is sent. The check takes under a minute.

  1. Open your browser developer tools with F12, or Cmd+Option+I on a Mac, and select the Network tab.
  2. Reload the page and let it finish. You will see the page's own files, its web fonts, and one anonymous page-view request. Nothing has been typed yet, so none of them can contain your headers.
  3. Click the clear icon in the Network tab so that the log is empty.
  4. Paste real headers into any lane and read the result.
  5. Look at the Network tab again. It is still empty. For extra proof, turn on offline mode after the page loads and every lane keeps working.

Only two things can add a line to that log, and neither carries your headers. Submitting the feedback form sends the vote and comment you typed. Typing characters in a script the page has not displayed yet, such as Cyrillic or Greek, can make the browser fetch the matching font file, and that request names only the font.

2http never sends a request on your behalf: the request builder writes code for you to run, and the meta inspector reads source you paste instead of fetching a URL. The production site also sends a Content-Security-Policy header that tells your browser to refuse connections to anywhere except this site and the anonymous analytics endpoint.

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