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Reference

Quick references for DNS record types, HTTP security headers, HTTP status codes, and TLS certificate errors.

DNS

DNS Record Types Reference - Every DNS Record Explained

A, AAAA, CNAME, MX, TXT, NS, SOA, CAA, PTR, SRV, and more. What each does, syntax, and examples.

Headers

Security Headers Reference - Every HTTP Security Header Explained

HSTS, CSP, X-Frame-Options, Referrer-Policy, Permissions-Policy, and more. What each does, recommended values, and how to verify.

HTTP Status Codes

The request succeeded; the response body carries the result.

HTTP 301 Moved Permanently

Permanent redirect — cacheable, passes link equity, updates the indexed URL.

Temporary redirect via the Location header; the original URL stays indexed.

HTTP 403 Forbidden

The server understood the request but refuses to authorize it.

HTTP 404 Not Found

The requested resource does not exist at this URL.

HTTP 429 Too Many Requests

Rate limited — slow down and honor the Retry-After header.

HTTP 500 Internal Server Error

Generic server-side failure; the request was valid but the server errored.

HTTP 502 Bad Gateway

Gateway or proxy received an invalid response from an upstream server.

HTTP 503 Service Unavailable

Service temporarily unavailable from overload or maintenance; usually transient.

TLS Errors

TLS Error: Certificate Expired

Causes, symptoms, and step-by-step resolution for expired TLS certificates using the TLS Inspector.

TLS Error: Hostname Mismatch

The certificate does not cover the domain you are connecting to. How to diagnose and fix a hostname mismatch error.

TLS Error: Incomplete Certificate Chain

Why some clients fail while others work, and how to serve the full chain to fix incomplete chain errors.