Last Updated on Aug 6, 2026 by Nurul Afsar
Every time a browser, app, or search engine bot requests a page on your website, your server sends back a three digit number called an HTTP status code. Most visitors never see these codes, but they tell browsers, crawlers, and developers exactly what happened with that request: whether it succeeded, got redirected, failed because of something the visitor did, or failed because of something on the server. For anyone running an online store, understanding these codes is not just a technical detail. It affects how Google crawls and indexes your site, how customers experience checkout and product pages, and how quickly problems get diagnosed when something breaks.
This guide organizes every standard HTTP status code by its numeric category, explains what each one means in plain language, and points out which codes matter most for ecommerce sites and SEO.
What Are HTTP Status Codes?
An HTTP status code is a standardized response a web server sends alongside every request a browser or crawler makes. The code itself is a number between 100 and 599, and the first digit tells you which broad category the response falls into. Codes are defined by the official HTTP semantics standard, RFC 9110, and maintained by the Internet Assigned Numbers Authority.
Status codes are grouped into five categories based on their first digit:
| Range | Category | What It Means |
|---|---|---|
| 1xx | Informational | The request was received and processing is continuing. |
| 2xx | Success | The request was received, understood, and accepted. |
| 3xx | Redirection | Further action is needed to complete the request, usually a redirect to another URL. |
| 4xx | Client Error | The request contains something the server could not process, and the fault is on the client side. |
| 5xx | Server Error | The server failed to fulfill a valid request due to a problem on its own end. |
1xx: Informational Responses
These codes are sent before the final response and are rarely seen directly by users or SEO tools, but they play a role in how modern connections are negotiated.
| Code | Name | Meaning |
|---|---|---|
| 100 | Continue | The server has received the request headers and the client should proceed to send the request body. |
| 101 | Switching Protocols | The server agrees to switch protocols as requested by the client, such as upgrading to WebSocket. |
| 102 | Processing | The server has received the request and is processing it, but no response is available yet. Used in WebDAV. |
| 103 | Early Hints | Used to return some response headers before the final response, allowing browsers to preload resources. |
2xx: Success Codes
These are the codes you want to see. They confirm a request was received, understood, and completed successfully.
| Code | Name | Meaning |
|---|---|---|
| 200 | OK | The request succeeded. This is the standard response for a successful page load or API call. |
| 201 | Created | The request succeeded and a new resource was created, commonly used after a POST request such as creating an account. |
| 202 | Accepted | The request was accepted for processing, but the processing has not been completed yet. |
| 203 | Non Authoritative Information | The request succeeded, but the returned metadata is from a source other than the origin server. |
| 204 | No Content | The request succeeded, but there is no content to return, often used after a delete action. |
| 205 | Reset Content | The request succeeded and asks the client to reset the document view, such as clearing a form. |
| 206 | Partial Content | The server is delivering only part of the resource due to a range header, commonly used for video streaming and large file downloads. |
3xx: Redirection Codes
Redirection codes tell a browser or crawler that a resource has moved somewhere else. These are among the most important codes for SEO because the wrong redirect type can waste crawl budget, dilute ranking signals, or send both users and search engines to the wrong place.
| Code | Name | Meaning |
|---|---|---|
| 300 | Multiple Choices | The request has more than one possible response and the client should choose one. |
| 301 | Moved Permanently | The resource has permanently moved to a new URL. Search engines transfer ranking signals to the new URL over time. |
| 302 | Found | The resource has temporarily moved to a different URL. The original URL is expected to be used again in the future. |
| 303 | See Other | The response can be found at a different URL using a GET request, commonly used after form submissions. |
| 304 | Not Modified | The resource has not changed since the last request, so the client can use its cached version. |
| 307 | Temporary Redirect | Similar to 302, but guarantees the request method and body will not change on the redirected request. |
| 308 | Permanent Redirect | Similar to 301, but guarantees the request method and body will not change on the redirected request. |
If you want a deeper breakdown of when to use a permanent versus a temporary redirect and how each affects rankings, see our guides on the 301 redirect and the 302 status code.
4xx: Client Error Codes
A 4xx code means the server believes the problem is with the request itself, whether that is a broken link, missing authentication, or a malformed submission. For ecommerce sites, this category directly affects checkout completion, form submissions, and API integrations.
| Code | Name | Meaning |
|---|---|---|
| 400 | Bad Request | The server could not understand the request due to invalid syntax, malformed data, or missing required information. |
| 401 | Unauthorized | The request requires valid authentication credentials that were not provided or were incorrect. |
| 402 | Payment Required | Reserved for future use, occasionally used by APIs to indicate a payment is required to continue. |
| 403 | Forbidden | The server understood the request but refuses to authorize it, often due to permission restrictions. |
| 404 | Not Found | The server cannot find the requested resource. One of the most common codes on any website. |
| 405 | Method Not Allowed | The request method is known but not supported by the target resource, such as using POST on a GET only endpoint. |
| 406 | Not Acceptable | The server cannot produce a response matching the list of acceptable formats defined in the request headers. |
| 407 | Proxy Authentication Required | The client must authenticate with a proxy before the request can proceed. |
| 408 | Request Timeout | The server timed out waiting for the request, often due to a slow or interrupted connection. |
| 409 | Conflict | The request conflicts with the current state of the resource, such as two updates competing for the same record. |
| 410 | Gone | The resource is no longer available and has been permanently removed, with no forwarding address. |
| 411 | Length Required | The server requires a Content Length header that was not supplied. |
| 412 | Precondition Failed | A condition set in the request headers was not met by the server. |
| 413 | Payload Too Large | The request body is larger than the server is willing or able to process, often seen with large file uploads. |
| 414 | URI Too Long | The requested URL is longer than the server can interpret. |
| 415 | Unsupported Media Type | The request format is not supported by the server, such as sending XML when only JSON is accepted. |
| 416 | Range Not Satisfiable | The requested byte range cannot be fulfilled for the resource. |
| 417 | Expectation Failed | The expectation given in the request Expect header could not be met by the server. |
| 418 | I’m a teapot | A joke code from an April Fools RFC, occasionally implemented by servers as an easter egg. Not used in production systems. |
| 421 | Misdirected Request | The request was directed at a server that is not able to produce a response. |
| 422 | Unprocessable Content | The server understands the request and its syntax is correct, but it cannot act on the instructions contained within it, commonly seen on checkout and API form validation failures. |
| 423 | Locked | The resource being accessed is locked, used in WebDAV. |
| 424 | Failed Dependency | The request failed because it depended on another request that failed, used in WebDAV. |
| 425 | Too Early | The server is unwilling to risk processing a request that might be replayed. |
| 426 | Upgrade Required | The server refuses to process the request using the current protocol and requires an upgrade. |
| 428 | Precondition Required | The server requires the request to be conditional, typically to prevent lost update conflicts. |
| 429 | Too Many Requests | The client has sent too many requests in a given amount of time, commonly triggered by rate limiting on APIs. |
| 431 | Request Header Fields Too Large | The server refuses to process the request because its header fields are too large. |
| 451 | Unavailable For Legal Reasons | The resource is unavailable due to a legal demand, such as government mandated content removal. |
Two of the most common 4xx codes ecommerce teams run into are covered in more depth here: what a 400 status code means and how to fix it, and what a 422 status code means and how to fix it.
5xx: Server Error Codes
A 5xx code means the server itself failed to complete a valid request. These are the most urgent codes to monitor because they usually indicate the site, or part of it, is down for every visitor, not just one.
| Code | Name | Meaning |
|---|---|---|
| 500 | Internal Server Error | A generic error indicating something went wrong on the server, without a more specific message available. |
| 501 | Not Implemented | The server does not support the functionality required to fulfill the request. |
| 502 | Bad Gateway | The server, acting as a gateway or proxy, received an invalid response from an upstream server. |
| 503 | Service Unavailable | The server is temporarily unable to handle the request, often due to maintenance or overload. |
| 504 | Gateway Timeout | The server, acting as a gateway or proxy, did not receive a timely response from an upstream server. |
| 505 | HTTP Version Not Supported | The server does not support the HTTP protocol version used in the request. |
| 506 | Variant Also Negotiates | A server configuration error where content negotiation results in a circular reference. |
| 507 | Insufficient Storage | The server cannot store the representation needed to complete the request, used in WebDAV. |
| 508 | Loop Detected | The server detected an infinite loop while processing the request, used in WebDAV. |
| 510 | Not Extended | Further extensions to the request are required for the server to fulfill it. |
| 511 | Network Authentication Required | The client needs to authenticate to gain network access, commonly seen on public WiFi login pages. |
The most frequent server error by far is a 500. For a full walkthrough of common causes and fixes, see how to fix 500 internal server errors.
Why HTTP Status Codes Matter for Ecommerce SEO
Search engines rely on status codes to decide how to treat every URL they crawl. A store with frequent, unresolved errors sends the wrong signals at scale:
- Unresolved 404s on product or category pages waste crawl budget and can quietly remove pages from the index.
- Using a 302 where a 301 belongs can delay or prevent ranking signals from transferring to a new URL after a rebrand, platform migration, or product retirement.
- Frequent 5xx errors during traffic spikes, such as a sale or promotion, can cause Googlebot to slow its crawl rate on your entire site.
- 422 and 400 errors on checkout, account creation, or newsletter forms directly cost conversions, even when the rest of the site is healthy.
- 429 errors on product feeds or app integrations can silently break inventory sync, pricing updates, or marketplace listings.
How to Monitor and Fix Status Code Issues on Your Store
Most status code problems fall into a few recurring patterns: broken internal links, incorrect redirect types left over from a migration, server resource limits being hit during traffic spikes, or form validation errors that were never surfaced to the user in plain language. Google Search Console, server log analysis, and a Semrush or Screaming Frog crawl are the fastest ways to catch these issues before they affect rankings or revenue.
If your store is dealing with recurring server errors, checkout failures, or a redirect cleanup after a platform change, Numinix can audit your site’s status code health as part of our ecommerce SEO services, diagnose infrastructure level causes through our speed optimization services, or handle ongoing monitoring through our security and support services.
Frequently Asked Questions
What is the most common HTTP status code?
200 OK is by far the most common, since it is returned for every successful page load. Among error codes, 404 Not Found and 500 Internal Server Error are the two most frequently encountered on live websites.
Is a 404 error bad for SEO?
An occasional 404 on a page that genuinely no longer exists is normal and expected. The problem is unresolved 404s on pages that still receive internal links or backlinks, since those waste crawl budget and lose any ranking value the page had built up.
What is the difference between a 301 and a 302 redirect?
A 301 tells search engines a page has moved permanently and passes ranking signals to the new URL. A 302 signals a temporary move, and search engines generally keep the original URL indexed rather than transferring signals to the new one.
Why do I see different status codes for the same error?
Different platforms, servers, and applications sometimes use slightly different codes for similar situations. For example, a failed form submission might return a 400 on one system and a 422 on another, depending on how the developer built the validation logic.
Do I need to fix every 4xx and 5xx error on my site?
Not every one requires action. A 404 on a genuinely discontinued product page is expected. Priority should go to errors on pages with existing traffic, backlinks, or internal links, and to any 5xx error, since those indicate the server itself is having trouble.