In order to properly compare and match JIDs, a normalization and prepping step is required by RFC 6122 . The responsibility for such normalization is split between the server and client, where the server is expected to prep any JID slots that it recognizes, particulary those related to stanza routing and roster items. However, the server can not prep JID slots that it does not understand, and so those are left for the client to process.
In some environments (in particular, browser based environments), a client does not have access to the various Unicode and internationalization libraries necessary to properly prep and normalize a JID. For those situations, this protocol defines a way for a client to ask a server to normalize a JID on its behalf.
If a server supports JID prep queries, it MUST specify the 'urn:xmpp:jidprep:0' feature in its service discovery information features as specified in Service Discovery (XEP-0030)  and the Entity Capabilities profile specified in Entity Capabilities (XEP-0115) .
The JID prep service MAY be supported through the use of an external component (Jabber Component Protocol (XEP-0114) ); in which case, the component MUST return an identity of "component/jidprep" in addition to the "urn:xmpp:jidprep:0" feature.
In order to request prepping for a JID, the client sends an <iq/> stanza of type "get" to the server, containing a <jid/> element qualified by the 'urn:xmpp:jidprep:0' namespace and whose XML character data is the JID in question:
The server MUST return either an IQ-result or an IQ-error. When returning an IQ-result, the server sends an <iq/> staza of type='result' containing a <jid/> element qualifed by the 'urn:xmpp:jidprep:0' namespace and whose XML character data MUST be the prepped and normalized version of the requested JID:
If an IQ-error is returned, then it SHOULD specify an error condition of <jid-malformed/> if the given JID could not be processed to a normalized form:
If a client has the ability to perform the prepping and normalization process itself, it SHOULD NOT make a JID prep request to the server.
Upon a successful response, the client SHOULD cache the result, mapping the original JID to the normalized version.
In order to reduce the number of queries made by clients, the server MUST enforce normalization rules for any JID slots understood by the server (e.g. the to and from attributes, roster item JIDs, etc). 
As the process for normalizing a JID can be resource intensive, there is a possibility for denial of service attacks. A server MAY rate limit the number of requests to prevent such attacks. Likewise, the server MAY only respond to requests from users that are local to the server.
This document requires no interaction with the Internet Assigned Numbers Authority (IANA) .
If the protocol defined in this specification undergoes a revision that is not fully backwards-compatible with an older version, the XMPP Registrar shall increment the protocol version number found at the end of the XML namespaces defined herein, as described in Section 4 of XEP-0053.
The XMPP Registrar  includes a category of "component" in its registry of Service Discovery identities (see <https://xmpp.org/registrar/disco-categories.html>); as a result of this document, the Registrar includes a type of "jidprep" to that category.
The registry submission is as follows:
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The Extensible Messaging and Presence Protocol (XMPP) is defined in the XMPP Core (RFC 6120) and XMPP IM (RFC 6121) specifications contributed by the XMPP Standards Foundation to the Internet Standards Process, which is managed by the Internet Engineering Task Force in accordance with RFC 2026. Any protocol defined in this document has been developed outside the Internet Standards Process and is to be understood as an extension to XMPP rather than as an evolution, development, or modification of XMPP itself.
The primary venue for discussion of XMPP Extension Protocols is the <firstname.lastname@example.org> discussion list.
Discussion on other xmpp.org discussion lists might also be appropriate; see <http://xmpp.org/about/discuss.shtml> for a complete list.
Errata can be sent to <email@example.com>.
The following requirements keywords as used in this document are to be interpreted as described in RFC 2119: "MUST", "SHALL", "REQUIRED"; "MUST NOT", "SHALL NOT"; "SHOULD", "RECOMMENDED"; "SHOULD NOT", "NOT RECOMMENDED"; "MAY", "OPTIONAL".
6. Extensible Messaging and Presence Protocol (XMPP): Address Format <https://datatracker.ietf.org/doc/draft-ietf-xmpp-6122bis/>. Work in progress.
7. The Internet Assigned Numbers Authority (IANA) is the central coordinator for the assignment of unique parameter values for Internet protocols, such as port numbers and URI schemes. For further information, see <http://www.iana.org/>.
8. The XMPP Registrar maintains a list of reserved protocol namespaces as well as registries of parameters used in the context of XMPP extension protocols approved by the XMPP Standards Foundation. For further information, see <https://xmpp.org/registrar/>.
Note: Older versions of this specification might be available at http://xmpp.org/extensions/attic/
Initial published version approved by the XMPP Council.