What do HTTP status codes mean? This complete guide explains 2xx, 3xx, 4xx, and 5xx status codes, how they affect SEO, and how to check them on any URL for free.
Every time your browser loads a webpage, the server responds with an HTTP status code. Most of the time everything works and you never notice. But when something goes wrong — or when the wrong code is silently returned — your SEO can suffer without any obvious sign on screen.
What Are HTTP Status Codes?
HTTP status codes are three-digit numbers that web servers send in response to browser requests. They're grouped into five classes based on their first digit:
- 1xx — Informational: Request received, continuing process
- 2xx — Success: The request was received, understood, and accepted
- 3xx — Redirection: Further action needs to be taken to complete the request
- 4xx — Client Error: The request contains bad syntax or cannot be fulfilled
- 5xx — Server Error: The server failed to fulfill an apparently valid request
The Most Important Status Codes
200 OK
The standard successful response. The server found the page and returned it normally. This is what you want for all your live, indexable content.
301 Moved Permanently
The page has permanently moved to a new URL. Search engines transfer ranking signals from the old URL to the new one. Use this for all permanent redirects.
302 Found (Temporary Redirect)
The page has temporarily moved. Search engines keep the original URL in their index. Use only for genuinely temporary redirects — using a 302 when you mean 301 is a common and costly SEO mistake.
304 Not Modified
The page hasn't changed since the browser last requested it — so the server doesn't resend the full content. The browser loads the cached version. This is good for performance.
400 Bad Request
The server couldn't understand the request due to invalid syntax. Often caused by malformed URLs or corrupted request data.
401 Unauthorized
Access requires authentication. The user needs to log in before accessing this resource.
403 Forbidden
The server understood the request but refuses to authorize it. Different from 401 — authentication won't help here. Often caused by file permission issues or IP blocks.
404 Not Found
The server can't find the requested page. This is the most common error users encounter. From an SEO perspective, 404 pages waste crawl budget and lose any link equity pointing to that URL. Broken pages should be redirected with a 301 to the most relevant live page.
410 Gone
Like 404, but permanent. The page existed and has been deliberately removed with no replacement. This signals to Google to remove the URL from its index faster than a 404.
500 Internal Server Error
The server encountered an unexpected condition that prevented it from fulfilling the request. If Google's crawler hits 500 errors, it stops crawling those pages — a serious crawlability problem.
503 Service Unavailable
The server is temporarily unable to handle the request — typically due to maintenance or overload. If your server returns 503 with a Retry-After header during scheduled maintenance, Google will come back and try again without penalizing you.
Why HTTP Status Codes Matter for SEO
- 404 errors waste Google's crawl budget — the limited number of pages Google crawls per site visit. Too many 404s and Google crawls fewer of your important pages.
- Soft 404s are pages that return a 200 status code but display a "page not found" type message. Google detects these and treats them as 404s — but they're harder to find and fix.
- 5xx errors tell Google your site has reliability problems. A server that frequently returns 500 errors may see reduced crawl frequency and ranking drops.
- 302 instead of 301 means ranking signals aren't fully transferred during page moves — your new URL builds authority slowly while the old one stays in the index.
How to Check HTTP Status Codes
A free HTTP headers checker lets you see exactly what status code any URL returns, along with all the response headers from the server. This is how you verify that your redirects are working correctly, diagnose 404 errors, and confirm your pages are returning 200 OK.
Check HTTP Response Headers Free →
Quick Checklist for a Healthy Site
- All live pages return 200 OK
- All moved or deleted pages return 301 (not 302) to a relevant destination
- No pages return 404 without a redirect to a relevant live URL
- No pages return 500 or 503 during normal operation
- No soft 404s — pages that look like errors but return 200
- Check your top 50 pages monthly using an HTTP headers tool
Running a regular HTTP status check across your key URLs catches these problems before they compound into ranking drops — especially after site migrations, redesigns, or CMS updates.