HTTP Status Codes & Web Standards

HTTP status code definitions, semantics, and header specifications referenced across this website are based on the current standards maintained by the Internet Engineering Task Force (IETF) and the Internet Assigned Numbers Authority (IANA):

• HTTP Semantics & Status Codes:
  • Core Standard: IETF RFC 9110 — HTTP Semantics (obsoleting RFC 7231 and RFC 2616)
  • Authoritative Registry: IANA HTTP Status Code Registry
  • Reference & Overview: Wikipedia: List of HTTP Status Codes

Much of the information described here is available in its original technical format from the IETF and W3C. Where possible, we have made a conscious effort to make this information accessible by using plain, easy-to-follow language, and by giving practical examples.

Information and guides about how to use this information — for example, the descriptive explanations about HTTP Status Codes and how to create custom 404 error pages — are all original, written by us, and we retain copyrights over this material.

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Domain Name System (DNS) Standards

Our DNS Lookup tool inspects and translates zone records (A, AAAA, CNAME, MX, TXT, NS, SOA, CAA, PTR) into plain English, referencing the fundamental architecture and root management specifications:

• DNS Architecture & Specification:
  • Concepts & Facilities: IETF RFC 1034 — Domain Names: Concepts and Facilities
  • Implementation & Records: IETF RFC 1035 — Domain Names: Implementation and Specification
  • Authoritative Registry: IANA Root Zone Database
  • Reference & Overview: Wikipedia: Domain Name System

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SSL / TLS & Encryption Standards

Our SSL Checker assesses certificate validity, trust chain integrity, cryptographic strength, and domain coverage using current Transport Layer Security specifications and certificate authority governance:

• Transport Layer Security (TLS):
  • Current Protocol Standard: IETF RFC 8446 — The Transport Layer Security (TLS) Protocol Version 1.3
  • X.509 PKI Certificates: IETF RFC 5280 — Internet X.509 Public Key Infrastructure Certificate Profile
  • Industry Baseline: CA/Browser Forum — Baseline Requirements for TLS Server Certificates
  • Reference & Overview: Wikipedia: Transport Layer Security

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Robots Exclusion & Sitemaps Standards

Our Robots.txt & Sitemap Validator parses and verifies web crawler directives and XML site maps against officially published Internet standards:

• Robots Exclusion Protocol:
  • Official Standard: IETF RFC 9309 — Robots Exclusion Protocol
  • Reference & Overview: Wikipedia: Robots Exclusion Standard
• XML Sitemaps Protocol:
  • Official Specification: sitemaps.org — XML Sitemap Protocol Specification (Google, Microsoft, Yahoo)
  • Reference & Overview: Wikipedia: Sitemaps

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Social Metadata & Rich Sharing Standards

Our Social Card Preview verifies metadata embedded in web pages for rendering cards across social media networks, messaging clients, and search engines:

• Open Graph Protocol:
  • Official Specification: The Open Graph Protocol (ogp.me)
  • Reference & Overview: Wikipedia: Open Graph Protocol
• X (Twitter) Cards:
  • Technical Reference: X Developer Platform — Cards Markup Guide
• Structured Data & Semantic Web:
  • Community Vocabulary: Schema.org
  • W3C Standard: W3C JSON-LD 1.1 Specification

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Email DNS & Deliverability Standards

Our Email DNS & Deliverability Checker evaluates domain authentication, anti-spoofing policies, and mail exchange configuration against established Internet Engineering Task Force (IETF) RFC specifications and authoritative documentation:

• Sender Policy Framework (SPF):
  • Specification: IETF RFC 7208 — Sender Policy Framework for Authorizing Use of Domains in Email
  • Reference & Overview: Wikipedia: Sender Policy Framework
• Domain-based Message Authentication, Reporting, and Conformance (DMARC):
  • Specification: IETF RFC 7489 — Domain-based Message Authentication, Reporting, and Conformance
  • Reference & Overview: Wikipedia: DMARC
• DomainKeys Identified Mail (DKIM):
  • Specification: IETF RFC 6376 — DomainKeys Identified Mail Signatures
  • Reference & Overview: Wikipedia: DomainKeys Identified Mail
• Mail Exchanger (MX Records & SMTP Routing):
  • Specification: IETF RFC 5321 — Simple Mail Transfer Protocol (Section 5: Mail Routing)
  • Reference & Overview: Wikipedia: MX record

We synthesize these technical specifications into plain-English diagnostics and scoring to help domain owners maintain optimal email deliverability and satisfy authentication requirements enforced by major mailbox providers like Google, Microsoft, and Yahoo.

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Web Hyperlink & Link Validation Standards

Our Link Checker extracts and evaluates all anchor hyperlinks embedded across modern dynamic web pages, verifying HTTP response statuses, redirect destinations, and robots crawler access rules against governing Internet specifications:

• HTML Anchor Hyperlinks:
  • Specification: W3C HTML 5.2 — Section 4.6 (Links and Hyperlink Semantics)
  • Reference & Overview: Wikipedia: Hyperlink
• HTTP Protocol Semantics & Method Checks:
  • Core Standard: IETF RFC 9110 — HTTP Semantics (Status Codes, HEAD, and GET methods)
  • Status Registry: IANA HTTP Status Code Registry
• Robots Exclusion Verification:
  • Crawler Directives: IETF RFC 9309 — Robots Exclusion Protocol

The tool renders dynamic JavaScript DOM trees to discover all client-side anchor references, polite worker throttling to respect origin server capacity, and categorizes links by HTTP status class (2xx, 3xx, 4xx/5xx, robots exclusions, and connection errors).