"X-" Considered Harmful

Document Type Replaced Internet-Draft (individual)
Author Peter Saint-Andre 
Last updated 2014-07-02 (latest revision 2010-10-19)
Replaced by RFC 6648
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This Internet-Draft is no longer active. A copy of the expired Internet-Draft can be found at


Many application protocols use named parameters to represent data (for example, header fields in Internet mail messages and HTTP requests). Historically, protocol designers and implementers have often differentiated between "standard" and "experimental" parameters by prefixing experimental parameters with the string "X-". This document argues that, on balance, the "X-" convention has more costs than benefits.


Peter Saint-Andre (psaintan@cisco.com)

(Note: The e-mail addresses provided for the authors of this Internet-Draft may no longer be valid.)