This document establishes a convention for use of JSON-encoded field values in HTTP header fields. Editorial Note (To be removed by RFC Editor before publication) Discussion of this draft takes place on the HTTPBIS working group mailing list (ietf-http-wg@w3.org), which is archived at <https://lists.w3.org/Archives/Public/ietf-http-wg/>. Working Group information can be found at <http://httpwg.github.io/>; source code and issues list for this draft can be found at <https://github.com/httpwg/http-extensions>. The changes in this draft are summarized in Appendix A.