Whether you’re a developer, webmaster, or SEO specialist, understanding HTTP status codes is critical for maintaining a well-functioning and secure website. These three-digit codes returned by web servers in response to client requests are fundamental to diagnosing errors, improving user experience, and securing site infrastructure.

In this guide, we’ll dive into what HTTP status codes are, how they work, and how mastering them—along with monitoring tools—can significantly enhance your site management practices.

What Are HTTP Status Codes?

HTTP status codes are standardized response messages issued by a server to indicate the result of a client’s request. Each code belongs to one of five response classes, defined by the first digit:

• 1xx – Informational
• 2xx – Success
• 3xx – Redirection
• 4xx – Client Errors
• 5xx – Server Errors

Correct usage and interpretation of these codes are essential for everything from SEO and performance optimization to error handling and security response.

1xx – Informational Responses

These codes indicate that the request has been received and processing is continuing.

• 100 Continue – Indicates the initial part of a request has been received and the client should continue.
• 101 Switching Protocols – The server is switching protocols as requested by the client.
• 103 Early Hints – Used to suggest resources the client should preload before the final response is sent.

These are primarily useful in advanced HTTP implementations, particularly HTTP/2 and HTTP/3.

2xx – Successful Responses

A 2xx code means the request was successfully received and processed.

• 200 OK – The standard response for successful requests.
• 201 Created – Indicates that a new resource has been created. Common in RESTful APIs.
• 202 Accepted – The request is accepted for processing, but not completed.
• 204 No Content – The server successfully processed the request but returns no content.

Using 204 No Content is a performance-friendly choice when you don’t need to return a payload, such as in AJAX interactions or polling mechanisms.

3xx – Redirection Responses

These codes inform the client that it must take additional action to complete the request.

• 301 Moved Permanently – The requested resource has been assigned a new permanent URI. Essential for SEO.
• 302 Found – Temporary redirect.
• 303 See Other – Redirects to another URI using a GET request.
• 307 Temporary Redirect – Similar to 302 but maintains request method.
• 308 Permanent Redirect – Maintains method and body like 307, but for permanent redirects.

Correct use of 301 vs. 302 is essential for managing site migrations and maintaining search engine visibility.

4xx – Client Error Responses

These indicate errors caused by the client, such as malformed requests or unauthorized access.

• 400 Bad Request – Generic client-side error due to malformed syntax.
• 401 Unauthorized – Authentication required or failed.
• 403 Forbidden – Access is understood but not permitted.
• 404 Not Found – The resource is not found. One of the most common HTTP errors.
• 405 Method Not Allowed – The request method is not supported for the resource.
• 429 Too Many Requests – Indicates the user has sent too many requests in a given amount of time (rate limiting).

Monitoring 401 and 403 codes can help detect brute-force login attempts or unauthorized resource access. Custom 404 pages can also reduce bounce rates and improve user retention.

5xx – Server Error Responses

These codes indicate server-side failures that require administrative attention.

• 500 Internal Server Error – A generic server error.
• 501 Not Implemented – The server does not recognize or support the method.
• 502 Bad Gateway – The server received an invalid response from an upstream server.
• 503 Service Unavailable – The server is temporarily unable to handle the request. Useful during maintenance.
• 504 Gateway Timeout – The server didn’t receive a timely response from an upstream source.

To diagnose 500-series errors effectively, use logging and APM tools, and monitor server load during high-traffic periods or deployments.

Understanding HTTP Flood Attacks and the Role of HTTP/HTTPS Monitoring

An HTTP flood attack is an application-layer DDoS attack that overwhelms a server with a large volume of seemingly legitimate HTTP requests. Unlike volumetric attacks that target bandwidth, HTTP floods aim to exhaust server resources such as CPU, memory, and database connections.

These attacks can be particularly insidious because the traffic appears normal—making it harder to detect using traditional firewalls or network-based intrusion detection systems.

Common symptoms of an HTTP flood include:

• A surge in request rate to endpoints like login or search
• Backend services becoming unresponsive
• Increased latency or timeouts for real users

HTTP/HTTPS Monitoring plays a key role in mitigating such attacks. With real-time monitoring of HTTP request behavior, response codes, latency, and traffic patterns, administrators can detect anomalies early. Integration with alerting systems or web application firewalls (WAFs) helps in triggering automated responses to block malicious traffic.

If left unchecked, HTTP floods can degrade service quality, impact search rankings, and even cause full outages—making advanced monitoring a necessity, not a luxury.

DNS Flood Attacks and DNS Resolution Delays

A DNS flood attack targets DNS servers with a massive number of DNS query requests, often using randomized subdomains to bypass caching. The server must attempt to resolve each request, increasing load and causing delays.

This flood not only affects the DNS server itself but can also delay DNS resolution for legitimate users. These delays cascade across services that rely on DNS, such as websites, email, and APIs, potentially causing wide-scale disruptions.

Monitoring DNS traffic and limiting query rates are effective ways to mitigate the impact. Using anycast-based DNS providers and load balancing can also help distribute the traffic and minimize outages.

Practical Applications of HTTP Status Codes

SEO Monitoring

Search engines interpret HTTP status codes to index and rank pages. Persistent 404 or 500 errors can cause deindexing, while 301 redirects preserve link equity. Use tools like Google Search Console, Screaming Frog, and SEMrush to monitor site health.

Performance Optimization

HTTP status codes can signal performance bottlenecks. 204 No Content and 103 Early Hints can help reduce unnecessary load and improve load times, especially in environments using HTTP/2 or HTTP/3.

API Development

RESTful APIs rely heavily on correct status codes. Returning 201 for creation, 204 for deletions, or 429 for rate limiting ensures predictable client-server communication and simplifies debugging.

Security and Access Control

Spikes in 401, 403, or 405 responses may signal unauthorized scanning or brute-force attempts. Monitoring and alerting on these codes enables faster incident response and better access control.

Tools to Monitor HTTP Status Codes

• Browser DevTools – Inspect response headers directly.
• cURL/Wget – Command-line tools to test endpoints (curl -I).
• Online Checkers – Tools like HTTPStatus.io or Redirect Checker.
• Log Aggregators – Use ELK Stack or Splunk for centralized monitoring.
• Uptime and Performance Monitoring – Services like ClouDNS, UptimeRobot, or Pingdom can track non-200 responses and monitor for anomalies.

Conclusion

Mastering HTTP status codes is a foundational skill for modern site management. Beyond just signaling errors or success, these codes influence SEO, performance, usability, and even security. Coupled with proactive monitoring—especially HTTP/HTTPS Monitoring—they can provide critical visibility into site behavior and health.