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HTTP status codes are essential for web developers, DevOps engineers, and cybersecurity professionals. They help diagnose issues, optimize performance, and secure web applications. Below is a detailed breakdown with practical commands and troubleshooting steps.
🔷 1XX – Informational
▸ 100 Continue: The server acknowledges the request headers; the client should proceed with the body.
▸ 101 Switching Protocols: The server agrees to switch protocols (e.g., HTTP to WebSocket).
▸ 102 Processing: Used in long-running requests (common in WebDAV).
▸ 103 Early Hints: Server hints at resources to preload before the final response.
Command to check headers (Linux):
curl -I https://example.com
🔷 2XX – Success
▸ 200 OK: Standard successful response.
▸ 201 Created: Resource successfully created (common in REST APIs).
▸ 202 Accepted: Request accepted but processing isn’t complete.
▸ 204 No Content: Success, but no body returned (common in DELETE requests).
▸ 206 Partial Content: Used for chunked downloads (e.g., video streaming).
Testing with cURL:
curl -X POST https://api.example.com/data -H "Content-Type: application/json" -d '{"key":"value"}'
🔷 3XX – Redirection
▸ 301 Moved Permanently: SEO-critical—update bookmarks and links.
▸ 302 Found: Temporary redirect (may change HTTP method).
▸ 304 Not Modified: Cached response still valid (saves bandwidth).
▸ 307 Temporary Redirect: Forces same HTTP method (safer than 302).
Check redirect chain:
curl -L -v https://example.com 2>&1 | grep -i "Location:"
🔷 4XX – Client Errors
▸ 400 Bad Request: Fix malformed syntax (check JSON/XML).
▸ 401 Unauthorized: Authentication needed (use `-u` in cURL).
▸ 403 Forbidden: Permission denied (check file/folder permissions).
▸ 404 Not Found: Validate URLs (audit broken links).
▸ 429 Too Many Requests: Implement rate limiting (e.g., `nginx` or iptables).
Debugging 403/404:
Check file permissions (Linux) ls -la /var/www/html Test authentication curl -u user:pass https://api.example.com/secure
🔷 5XX – Server Errors
▸ 500 Internal Error: Check server logs (`/var/log/nginx/error.log`).
▸ 502 Bad Gateway: Proxy/upstream server failure.
▸ 503 Service Unavailable: Server overloaded (scale resources).
▸ 504 Gateway Timeout: Increase timeout in `nginx/apache`.
Log inspection:
tail -f /var/log/nginx/error.log | grep "500"
You Should Know:
- Rate Limiting with
iptables:iptables -A INPUT -p tcp --dport 80 -m limit --limit 25/minute --limit-burst 100 -j ACCEPT
- HTTP/2 Testing:
curl --http2 -I https://example.com
- Bypass Cache (Force 200):
curl -H "Cache-Control: no-cache" https://example.com
What Undercode Say:
HTTP status codes are the backbone of web communication. Mastering them accelerates debugging and hardening of web apps. For DevOps, automate status code monitoring with tools like `Prometheus` and Grafana. For security, always audit 4XX/5XX responses—they reveal misconfigurations and attack vectors.
Expected Output:
HTTP/2 200 server: nginx content-type: text/html
Prediction:
As APIs dominate modern apps, expect more granular status codes (e.g., 423 Locked for resource contention). AI-driven debugging tools will auto-resolve common 5XX errors by 2026.
URLs:
References:
Reported By: Bonagirisandeep Http – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
