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PROTOCOL RADAR // HTTP STATUS INDEX

Comprehensive HTTP status code directory. Instant search across standard RFC 9110 statuses (1xx-5xx), Cloudflare 520-530 edge errors & Nginx proxy responses with root causes & mitigation steps.

DATABASE: 50+ STATUS CODES
MATCHING STATUS RECORDS: 50 CODES

PROTOCOL SPECIFICATION

RFC 9110
200

OK

2xx SUCCESSFUL
CACHING: Cacheable by default

Standard response for successful HTTP requests. The actual response will depend on the request method used (GET, POST, HEAD).

COMMON CAUSES / OCCURRENCE:
  • Server completed request processing normally.
  • Payload returned in response body.
RECOMMENDED MITIGATION / ACTION:
  • No remedial action necessary.
  • Optionally set Cache-Control headers for CDN acceleration.
RAW HTTP HEADER SNIPPET: 
HTTP/1.1 200 OK
Content-Type: text/html; charset=UTF-8

IN-DEPTH GUIDE // HTTP RESPONSE CODES, REST CONVENTIONS & EDGE TROUBLESHOOTING

Understanding RFC 9110 status code semantics, idempotency, caching directives, and Cloudflare 5xx edge troubleshooting.

HTTP Status Code Classification

The Hypertext Transfer Protocol (HTTP) standardizes response status codes into five distinct three-digit decimal classes, defined under the IETF Internet Standard RFC 9110:

  • 1xx (Informational): Request received, continuing process (e.g. 100 Continue, 101 Switching Protocols).
  • 2xx (Successful): The action was successfully received, understood, and accepted (e.g. 200 OK, 201 Created).
  • 3xx (Redirection): Further action must be taken to complete request (e.g. 301 Permanent, 302 Temporary, 304 Not Modified).
  • 4xx (Client Error): Request contains bad syntax or cannot be fulfilled (e.g. 400 Bad Request, 403 Forbidden, 404 Not Found, 429 Rate Limit).
  • 5xx (Server Error): Server failed to fulfill an apparently valid request (e.g. 500 Internal, 502 Bad Gateway, 503 Service Unavailable).

Cloudflare 520–530 Edge Error Telemetry

When operating behind global edge CDN proxies, specialized 5xx codes indicate where in the network link failure occurred:

  • 521 Web Server Is Down: The origin server refused TCP connections on ports 80/443. Check if Nginx/Apache process crashed.
  • 522 Connection Timed Out: Cloudflare edge completed SYN packet but origin host never completed the three-way TCP handshake within 15 seconds. Commonly caused by server firewall rate-limiting or routing drops.
  • 524 A Timeout Occurred: TCP handshake succeeded, but origin backend did not respond with HTTP headers within 100 seconds (long-running database query or script hang).
  • 525 SSL Handshake Failed: Cryptographic TLS negotiation failed between edge proxy and origin SSL certificate.

Frequently Asked Questions

What is the difference between 301 and 302?

A 301 Moved Permanently instructs search crawlers and browsers to update link authority and cache the redirection forever. A 302 Found is temporary, preserving the original URL indexing.

What does HTTP 418 I'm a teapot signify?

Defined in RFC 2324 as an April Fools' joke for the Hyper Text Coffee Pot Control Protocol (HTCPCP), 418 has since become an official RFC 9110 reserved status used playfully by APIs to reject requests that cannot brew coffee.

What triggers Nginx 499 Client Closed Request?

Nginx logs 499 when an end user cancels a download, closes the tab, or hits a frontend timeout while Nginx was still waiting for upstream response from PHP-FPM, Node.js, or Python Gunicorn.

Is this database available offline?

Yes. The entire encyclopedia is 100% packaged inside client JavaScript memory with zero network dependencies.