IETF RFC Number Validator

RFC: the document series that defines the Internet

An RFC (Request for Comments) is a numbered technical document published by the IETF (Internet Engineering Task Force) and edited by the RFC Editor. Despite the name suggesting an informal draft, an RFC is in fact the formal, archival form of every Internet protocol — TCP, IP, HTTP, TLS, DNS, SMTP, JSON, MIME and thousands of others are RFCs. This validator checks the canonical format RFC NNNN (or just the integer) and helps you spot well-known specifications quickly.

The series started on 7 April 1969 with RFC 1, "Host Software", written by Steve Crocker while a graduate student at UCLA working on ARPANET. The "Request for Comments" name was deliberate: Crocker wanted to signal that the document was open to discussion and revision — a culture of rough consensus and running code that defines the IETF to this day. As of 2024 the count has crossed RFC 10000.

Format and validation rule

An RFC identifier is the literal string RFC followed by a positive integer. Whitespace between RFC and the number is optional. The canonical regex is:

/^RFC\s?\d{1,5}$/i        // RFC 793, RFC2616, rfc 9110
/^\d{1,5}$/               // bare number form: 793

There is no checksum or check digit — validity is binary: either the number exists in the RFC Editor's index or it does not. Numbers are assigned monotonically and never reused, even if the document is later obsoleted or marked Historic.

Status levels: Standards Track, BCP, Informational, Experimental, Historic

• Standards Track — the formal three-step ladder: Proposed Standard, Draft Standard, Internet Standard. In 2011 RFC 6410 collapsed the middle step, so today most stable protocols sit at Proposed Standard for years.
• BCP (Best Current Practice) — recommended operational practice. BCP 14 = RFC 2119 + RFC 8174, the famous MUST/SHOULD/MAY definition.
• Informational — useful background, no consensus requirement. The Tao of the IETF is an example.
• Experimental — work in progress, may or may not become a standard.
• Historic — superseded or abandoned, kept for reference.

Famous RFCs every engineer should recognise

• RFC 791 — IPv4 (1981).
• RFC 793 — TCP (obsoleted by RFC 9293 in 2022).
• RFC 1034 / 1035 — DNS concepts and implementation.
• RFC 2616 — HTTP/1.1 (now obsoleted by RFC 7230-7235, themselves obsoleted by the RFC 9110-9114 family).
• RFC 5246 — TLS 1.2; RFC 8446 — TLS 1.3.
• RFC 4180 — CSV; RFC 5322 — Internet email message format; RFC 7519 — JWT.
• RFC 9562 — UUID v6/v7/v8 (2024), replacing parts of the original RFC 4122.
• RFC 2324 — HTCPCP "I'm a teapot", an April Fools joke whose status code 418 is now baked into HTTP servers everywhere.

Updates vs Obsoletes

An RFC can be updated (adds clarifications, keeps the original number relevant) or obsoleted (a newer RFC fully replaces it). Both relationships are bidirectional in the RFC Editor metadata. Example: RFC 2616 is obsoleted by RFC 7230 and RFC 7230 is obsoleted by RFC 9110. Always check the latest entry before quoting a spec.

RFC vs Internet-Draft vs ISO vs IRTF

• Internet-Draft — temporary working document, expires after 6 months. Cite it as draft-ietf-quic-transport-34, never as RFC.
• ISO standards — formal, paywalled, member-vote driven. RFCs are free and pragmatic.
• IRTF — the Internet Research Task Force publishes RFCs too, but for research not standardisation (look for the IRTF stream).
• April Fools RFCs — tradition since RFC 527 (1973). Famous examples: 1149 (IP over avian carriers), 2324 (teapot), 6214 (IPv6 carriers), 8771 ("I-Star").

Where to look up an RFC

• rfc-editor.org/rfc/rfcNNNN — canonical HTML and TXT.
• datatracker.ietf.org — full history, including drafts, working group discussions and IESG ballots.
• tools.ietf.org — legacy alias, still works.

FAQ

Are RFCs free to read?

Yes, always. Every RFC is published in the public domain at rfc-editor.org with no paywall, no login, no DRM. This is a core IETF principle and a major contrast with ISO/IEC standards.

Does an RFC ever become an "Internet Standard"?

Rarely. The full STD designation (e.g. STD 5 = IP, STD 7 = TCP) requires demonstrated interoperability and is reserved for the most mature protocols. Most modern RFCs sit at Proposed Standard indefinitely — that is enough to mandate deployment.

Are April Fools RFCs real RFCs?

Yes — they have real RFC numbers and are archived alongside serious protocols. Some, like RFC 2324 (HTCPCP), have leaked into reality: HTTP status code 418 I'm a teapot is implemented in Node.js, Go, Django and most frameworks.

What is the difference between "Updates" and "Obsoletes"?

Updates means the old RFC still applies and the new one adds clarifications. Obsoletes means the new RFC fully replaces the old one — implementations should follow the new text. The metadata is reciprocal in the RFC index.

Are RFC numbers reused?

Never. Once assigned, a number is permanent — even Historic and joke RFCs keep their number. The series is monotonically increasing and currently sits above 10000.