HTTP Status Code Explainer

What Are HTTP Status Codes?

HTTP status codes are standardized codes sent by a server in response to a browser or client request. They indicate whether the request was successful, redirected, or encountered an error.

Common categories include:

• 1xx – Informational: Request received, continuing process.
• 2xx – Success: Request was successfully received, understood, and accepted (e.g., 200 OK).
• 3xx – Redirection: Further action needs to be taken by the client to complete the request (e.g., 301 Moved Permanently).
• 4xx – Client Errors: Request contains bad syntax or cannot be fulfilled (e.g., 404 Not Found).
• 5xx – Server Errors: Server failed to fulfill a valid request (e.g., 500 Internal Server Error).

Why It Matters

Knowing HTTP status codes is crucial for troubleshooting website downtime, server issues, and SEO problems. For example, multiple 5xx errors indicate server instability, while too many 404 pages can harm SEO.

Monitoring HTTP status codes helps you:

• Detect downtime or server errors quickly.
• Ensure search engines correctly index your site.
• Identify broken links or misconfigured redirects.
• Maintain a healthy user experience and reduce lost revenue.

Tips for Handling HTTP Status Codes

• Regularly monitor your site for 4xx and 5xx errors using automated checks.
• Fix broken links or set up proper redirects to preserve user experience and SEO authority.
• Ensure server configurations return the correct status codes (a 200 for a missing page is much worse than a 404).
• Use uptime monitoring tools to detect recurring issues and trace patterns over time.
• Differentiate between transient errors and persistent failures — a single 503 may not be worth alerting on, but ten in a row certainly is.
• Track status code trends so you can correlate errors with recent deploys, traffic spikes, or third-party API failures.

The Most Common HTTP Status Codes Explained

While there are dozens of HTTP status codes defined by the standards, you will encounter only about a dozen in everyday operations. Understanding what each one means is the foundation of debugging web applications.

2xx Success Codes

• 200 OK: The request succeeded and the server returned the requested content. The most common code on a healthy site.
• 201 Created: A new resource was successfully created, typically in response to a POST request. Common in REST APIs.
• 204 No Content: The request succeeded but the server is intentionally returning no body. Common for DELETE operations.
• 206 Partial Content: The server is sending only part of the resource, used for resumable downloads and video streaming.

3xx Redirection Codes

• 301 Moved Permanently: The resource has been permanently moved to a new URL. Search engines transfer ranking signals to the new location.
• 302 Found: Temporary redirect. The resource is at a different URL right now, but may move back. Search engines do not transfer authority.
• 304 Not Modified: The cached version is still valid, no need to download again. Critical for performance and bandwidth savings.
• 307 Temporary Redirect: Like 302, but guarantees the request method (GET, POST) is preserved.
• 308 Permanent Redirect: Like 301, but also preserves the request method. The modern recommended permanent redirect for non-GET requests.

4xx Client Error Codes

• 400 Bad Request: The server cannot understand the request because of malformed syntax. Usually a bug on the client side.
• 401 Unauthorized: Authentication is required but missing or invalid. The user needs to log in.
• 403 Forbidden: The server understood the request but refuses to authorize it. Different from 401 — credentials are present but insufficient.
• 404 Not Found: The requested resource does not exist. The most famous status code, often a sign of broken links.
• 405 Method Not Allowed: The HTTP method (GET, POST, etc.) is not supported for this resource.
• 408 Request Timeout: The client took too long to send the request. The server gave up waiting.
• 410 Gone: The resource was intentionally removed and will never come back. Stronger signal than 404 for SEO purposes.
• 429 Too Many Requests: The client is being rate-limited. Common when scraping or hitting an API too aggressively.

5xx Server Error Codes

• 500 Internal Server Error: A generic error indicating something went wrong on the server. The most common signal of an application bug.
• 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 the upstream server. Common with reverse proxies and load balancers.
• 503 Service Unavailable: The server is temporarily unable to handle requests, usually due to overload or maintenance. Often the right code to return during planned downtime.
• 504 Gateway Timeout: The gateway server did not receive a timely response from the upstream server.
• 520-527 Cloudflare-specific: Various errors generated by Cloudflare when it cannot reach or get a valid response from your origin server.

Status Codes and SEO

The status codes your server returns directly affect how search engines crawl, index, and rank your site. Getting them wrong can quietly tank your organic traffic, while getting them right helps maintain rankings during site changes.

• 200 for missing content is bad. If a page does not exist, return 404 — never 200 with a "page not found" message in the body. Soft 404s confuse search engines and waste crawl budget.
• 301 transfers ranking authority; 302 does not. Use 301 for permanent moves so the new URL inherits the old one's SEO value. Use 302 only for genuinely temporary situations.
• 410 is stronger than 404 for removed content. If you intentionally removed a page and it will never come back, 410 tells search engines to drop it faster than a 404 would.
• 503 for maintenance windows is correct. When your site is temporarily down for planned maintenance, return 503 with a Retry-After header so search engines know to come back later instead of penalizing you.
• 5xx errors hurt rankings if persistent. Search engines treat repeated server errors as a signal of poor quality. A few transient 500s are tolerated; weeks of them are not.
• 429 should not block legitimate crawlers. Make sure your rate limiting does not accidentally throttle Googlebot, Bingbot, or other search engine crawlers.

When Each Code Should Trigger an Alert

Not every non-2xx response needs to wake you up at 3 AM. Here is a practical guide for which status codes to alert on and how aggressively:

• 200, 201, 204: Healthy. No alert.
• 301, 302, 308: Expected for redirects. Alert only if a critical page suddenly returns one when it should not.
• 304: Cache validation, healthy. No alert.
• 400: Client error, usually a buggy client. Track in metrics, do not alert.
• 401, 403: Authentication issues. Alert only if rates spike unexpectedly.
• 404: Track but do not alert per request. A sudden spike in 404s after a deploy is worth investigating.
• 429: Rate limiting. Alert if it persists, since legitimate users may be affected.
• 500, 502, 503, 504: Real server errors. Alert immediately if more than a few occur in a short window.
• 520-527 (Cloudflare): Treat like 5xx — your origin is unreachable from the edge, which means real customers cannot reach you either.

The right alerting threshold depends on your traffic volume. A site with 10 requests per minute might alert on 1 error; a site with 10,000 requests per minute should alert on patterns and rates rather than individual errors.

Frequently Asked Questions

Is a 404 always bad for SEO?

No. 404s are a normal part of the web — pages get removed, URLs change, and content gets reorganized. Search engines understand this. What hurts SEO is having broken internal links pointing to 404 pages, or returning 200 instead of 404 for missing pages (a "soft 404"). A few 404s are fine; many of them, especially from your own site, are a problem.

What is the difference between 401 and 403?

401 Unauthorized means "you are not authenticated — please log in". 403 Forbidden means "you are authenticated, but you are not allowed to access this resource". The distinction matters: 401 prompts the user to log in, while 403 tells them they cannot access this even after logging in.

Should I use 301 or 302 for redirects?

Use 301 (Moved Permanently) for permanent moves where you want search engines to transfer ranking authority to the new URL. Use 302 (Found) for temporary redirects, A/B tests, or geographic redirects where you do not want search engines to update their index. When in doubt for a permanent move, prefer 301 — or 308 if you also need to preserve the HTTP method.

My site returns 502 errors intermittently. What does that mean?

A 502 Bad Gateway means your front-end server (like Nginx, Apache, or a CDN) cannot get a valid response from your back-end application. Common causes include the application crashing, timing out, running out of memory, or being overwhelmed by traffic. Check your application logs for errors during the time of each 502 to find the root cause.

Does this tool show real status codes from my server?

The HTTP Status Code Explainer above is a reference and lookup tool — it explains what each code means but does not perform live checks. To monitor your own site's actual status codes over time, sign up for a free UptyBots account and add your URL as a monitor target.