What Are HTTP Status Codes?
A Complete List & Insights for SEO

Each time a webpage is accessed, a request is sent to the server, and the server responds with an HTTP status code that tells browsers, search engines, and user agents what to do next. These status codes aren’t technical jargon (though they might feel that way)—they directly influence user experience, search engine indexing, and overall website performance. Frequent errors or misconfigured redirects can lead to lost traffic, poor rankings, and even search engine penalties.

An HTTP status code is a server’s way of responding to a request made by a browser, search engine, or user agent. When you enter a URL, your browser sends a client request, and the server responds with a status code that tells you what happened.

Think of it as ordering food at a restaurant:

• A 200 OK is like receiving your order exactly as requested.
• A 301 Moved Permanently is when the restaurant tells you they’ve moved to a new location.
• A 404 Not Found is when they tell you the dish you wanted is no longer on the menu.
• A 500 Internal Server Error is when the kitchen has a meltdown, and no food is coming out.

These codes help search engines understand which pages to index, which have moved, and which are no longer relevant.

HTTP response status codes fall into five broad categories:

• 1xx (Informational) – The request has been received, but further action is needed.
• 2xx (Success) – The request was successfully received and processed.
• 3xx (Redirection) – The requested resource has moved, and the client should use a new URL.
• 4xx (Client Errors) – Something went wrong on the user’s end (e.g., a missing page).
• 5xx (Server Errors) – The issue is on the web server’s side.

• 100 Continue – The request was received, and the client can proceed.
• 101 Switching Protocols – The server is switching to the requested protocol.
• 102 Processing – The server is handling the request but isn’t finished yet.

• 200 OK – The request was successful.
• 201 Created – A new resource was successfully created.
• 204 No Content – The request was processed, but there’s no content to return.

• 301 Moved Permanently – The resource has been permanently moved (important for SEO).
• 302 Found – The resource is temporarily at another URL.
• 307 Temporary Redirect – Like 302 but keeps the request method intact.
• 308 Permanent Redirect – Like 301 but more strict.

• 400 Bad Request – The request is malformed or contains invalid syntax.
• 401 Unauthorized – Authentication is required.
• 403 Forbidden – The request is understood but not allowed.
• 404 Not Found – The page is missing (bad for SEO if overused).
• 429 Too Many Requests – The client has sent too many requests in a short period.

• 500 Internal Server Error – A generic error indicating a problem on the server.
• 502 Bad Gateway – The server received an invalid response from an upstream server.
• 503 Service Unavailable – The server is down, often due to maintenance.
• 504 Gateway Timeout – The server didn’t get a timely response from another server.

While this list covers the standard HTTP status codes recognized across the web, some platforms and services use proprietary or non-standard status codes for internal operations. These custom codes are not part of the official HTTP specification and may vary depending on a website’s origin server, internal configuration, or third-party integrations. Since search engines and browsers do not universally recognize them, they are not included here.

Every HTTP response code plays a role in shaping your website’s search performance. Search engines rely on these codes to determine which pages should be indexed, which should be ignored, and which might signal underlying technical issues. Properly managing these signals can improve your rankings, while misconfigured or excessive errors can negatively impact your site’s visibility.

• 200 OK – Indicates a successfully loaded page. Search engines can crawl, index, and rank it as intended.
• 301 Moved Permanently – A crucial redirect for SEO, ensuring that authority from an old URL is transferred to a new location, preserving rankings and link equity.
• 410 Gone – A clear signal to search engines that a page has been intentionally removed, allowing for faster deindexing compared to a 404.

• 404 Not Found – While occasional 404s are natural, a large number of missing pages can signal poor site maintenance, reducing user experience and impacting rankings.
• 500 Internal Server Error – Frequent 5xx errors indicate server instability, which can cause search engines to crawl your site less often and impact rankings.
• 302 Found (Temporary Redirect) – Unlike a 301, a 302 does not pass full link equity, which can lead to fragmented ranking signals if misused.

HTTP response codes play a critical role in website security and trustworthiness. Search engines, browsers, and security tools analyze these codes to assess whether a site is safe for users—or if it poses a risk. Misconfigured or misleading responses can lead to serious consequences, including search engine penalties, security warnings, and blocked access.

1. Persistent 4xx or 5xx Errors Can Signal Site Instability
   Frequent 404 Not Found or 500 Internal Server Error responses might indicate server misconfigurations, abandoned websites, or compromised pages. In some cases, a misconfigured origin server may fail to properly process requests, leading to unnecessary errors. If a site returns too many of these errors, it could be flagged as unreliable or even unsafe.
2. Malicious Sites Use Deceptive HTTP Codes
   Cybercriminals often exploit HTTP status codes to deceive users and security scanners. For example, a 200 OK response on a hacked page might falsely indicate everything is fine—while, in reality, the page is delivering phishing scams, malware, or cloaked redirects. Some attackers even manipulate request header fields to obscure malicious activity, making it harder for security tools to detect threats.
3. Suspicious Redirect Chains Raise Red Flags
   Redirects (301, 302, and 307) are common and useful, but excessive or misleading redirections can mask malicious intent. Some harmful websites use long redirect chains to funnel users toward scam pages, malware downloads, or phishing sites. When a site repeatedly returns misleading redirects or improper error codes, it raises security concerns that could lead to search engines blocking access.
4. Improper Use of 404 and 410 Affects Security Monitoring
   A properly configured 404 Not Found or 410 Gone tells search engines and security tools that a page is intentionally missing. However, some malicious sites misuse these codes—either by serving false 404 errors to hide dangerous content or failing to use them when pages should be removed. In some cases, they may even return a generic error message instead of the appropriate response code, making it harder for search engines to interpret the issue. 
5. 5xx Server Errors Can Block Security Crawlers
   Security platforms like Google Web Risk rely on web crawlers to scan pages for threats. If a site consistently returns 503 Service Unavailable or 504 Gateway Timeout, it might prevent these crawlers from accessing and verifying the site’s legitimacy. Repeated 5xx errors can raise concerns that a site is intentionally obscuring content.