IRCv3 Capabilities

ElixIRCd supports modern IRC client features through the IRCv3 capability negotiation system. Capabilities are negotiated during the connection handshake using the CAP command.

Capability Negotiation Flow

Client: CAP LS 302
Server: CAP * LS :SASL=PLAIN EXTENDED-JOIN AWAY-NOTIFY MESSAGE-TAGS SERVER-TIME ...
Client: CAP REQ :EXTENDED-JOIN AWAY-NOTIFY MULTI-PREFIX
Server: CAP * ACK :EXTENDED-JOIN AWAY-NOTIFY MULTI-PREFIX
Client: CAP END

Supported Capabilities

SASL (sasl)

SASL authentication before registration completes.

• Announced as: SASL=PLAIN (since PLAIN is the only supported mechanism)
• Non-requestable via CAP REQ SASL alone — use SASL=PLAIN
• Actually: SASL=PLAIN is the full cap value; clients request it as SASL

Purpose: Allows authentication using SASL PLAIN before the connection registration completes. See SASL Authentication.

ACCOUNT-TAG (account-tag)

Attaches the authenticated account name to messages via message tags.

When active: Messages from identified users include account=AccountName in their tag list.

Example:

@account=Alice :Alice!alice@host PRIVMSG #channel :Hello!

ACCOUNT-NOTIFY (account-notify)

Sends notifications when users in shared channels identify or log out.

When a user identifies:

:Alice!alice@host ACCOUNT AliceAccount

When a user logs out:

:Alice!alice@host ACCOUNT *

AWAY-NOTIFY (away-notify)

Real-time notifications when users in shared channels set or remove their away status.

When a user sets away:

:Alice!alice@host AWAY :Out for lunch

When a user clears away:

:Alice!alice@host AWAY

CAP-NOTIFY (cap-notify)

Notifies clients when server capabilities change dynamically (e.g., after REHASH).

CHGHOST (chghost)

Notifies users in shared channels when someone’s hostname changes (e.g., via +x mode or CHGHOST).

Format:

:Alice!oldident@oldhostname CHGHOST newident newhostname

CLIENT-TAGS (client-tags)

Allows clients to attach vendor-specific client-only tags to messages. These tags are forwarded to other clients but not interpreted by the server.

Format: Tags prefixed with + are client-only:

@+typing=active TAGMSG #channel

EXTENDED-JOIN (extended-join)

Adds account name and real name to JOIN messages.

Standard JOIN:

:Alice!alice@host JOIN #channel

Extended JOIN:

:Alice!alice@host JOIN #channel AliceAccount :Alice's Real Name

The account field is * if the user is not identified.

INVITE-EXTENDED (invite-extended)

Adds account information to INVITE messages.

INVITE-NOTIFY (invite-notify)

When a user is invited to a channel, other channel members receive a notification:

:Alice!alice@host INVITE Bob #channel

(Sent to all channel members with this capability)

MULTI-PREFIX (multi-prefix)

Displays all status prefixes for users in NAMES replies and similar responses.

Without MULTI-PREFIX:

@Alice   ← shows only highest prefix

With MULTI-PREFIX:

@+Alice  ← shows all prefixes (op and voice)

MESSAGE-TAGS (message-tags)

Full IRCv3 message tag support. Enables the use of message tags for metadata attachment.

Enables:

• SERVER-TIME tags (time=)
• MSGID tags (msgid=)
• ACCOUNT-TAG tags (account=)
• Bot tags (+draft/bot)
• Client-only tags (+vendor/name)

SERVER-TIME (server-time)

Adds a time= tag to every message with the server’s timestamp in ISO 8601 format.

Example:

@time=2024-01-15T14:30:00.000Z :Alice!alice@host PRIVMSG #channel :Hello!

MSGID (msgid)

Adds a unique msgid= tag to every message.

Example:

@msgid=abc123xyz456 :Alice!alice@host PRIVMSG #channel :Hello!

MONITOR (monitor)

Efficient user tracking. Track when specific nicknames go online or offline.

See MONITOR command.

SETNAME (setname)

Allows clients to change their real name (GECOS) during an active session.

UHNAMES / extended-names (uhnames)

Extended NAMES reply — nicks are shown as nick!ident@host instead of just nick.

EXTENDED-UHLIST (extended-uhlist)

Extended user modes in WHO replies.

STS (sts)

Strict Transport Security. Announces TLS upgrade policy.

• Plaintext connections: sts=port=6697
• TLS connections: sts=duration=2592000

Non-requestable — informational only.

Not Implemented

Capability	Status
batch	Not implemented
echo-message	Not implemented
labeled-response	Not implemented
standard-replies	Not implemented

Note

The BATCH capability and associated features (message history replay, etc.) are not implemented in ElixIRCd. For server-side message history, use ChanServ or an external bouncer.