A command in IRC. Changes the channel "mode", i.e. enables or disables certain attributes for the channel. Usage is /mode, followed by a + followed by the letters of whatever attributes you want to add and/or a - followed by the letters of whatever attributes you want to remove, followed by any extra arguments certain letter attributes (o, v, k, l, or b) may take. Only an op can change the channel mode. Letter attributes commonly seen on most irc networks are:
  • t- If true, you must be an op to change the topic.
  • n- If true, you are not allowed to say anything in the channel unless you are actually in the channel. If n is false for a channel, a person outside the channel can actually type /msg #channel message from anywhere, and that person will say message in the channel as if that person were actually in the channel. This can get really weird, and is used more for spam than for anything else.
  • i- If true, the channel becomes invite-only, and no one can enter the channel unless a channel op types /invite nick.
  • m- "mute"- If true, nobody is allowed to talk in the channel unless they are an op or they have voice-- in other words, they must have the channel mode for that person be +o or +v.
  • p- If true, channel is "private", and if a user within the channel is /whoised by a user outside the channel, they will not see the user is in that channel.
  • s- If true, channel is "secret", and the channel will not be listed for anyone outside the channel who does a /list.
  • l- If true, channel has a limit. This attribute takes a number as an argument (/mode #channel +l number). While the channel is +l, no more than number people will be allowed in the channel at one time. In some channels, the limit is some random, purely cosmetic number which serves no purpose but looks "cool", such as 303 or 31337 or 2000.
  • k- "key"- If true, channel is passworded, and no one is allowed to enter without giving the password in their /join (/join #channel password). This attribute takes the intended channel password as an argument.
  • o- This attribute takes the name of a user as an attribute, and gives that user operator status. That user will then be a channel op and will be allowed to /mode, /kick, etc.
  • v- This attribute takes the name of a user as an attribute, and gives that user voice. If a user has voice, that means they are able to talk when the channel is +m (muted). If the channel is not muted, voice doesn't do anything at all, but sometimes people will give it to people just because those people are special. SPECIAL! Voiced people will have a + next to the channel they are voiced in in their /whois, and will be displayed as green in the graphical userlist of some IRC clients.
  • b- Ban. Sets a class of people to be banned. Takes one attribute, which is constructed by a nick followed by a ! followed by a username followed by a hostmask. Wildcard Expansion can be used. So, for example, *!mcc@*.swbell.net would ban anyone with any nick, the username "mcc", and a hostmask ending in swbell.net.
Multiple attributes can be set at once; for example, /mode channel +is-tk would turn on i and s but off t and k. If you want to op or voice multiple people, you must have an o or v for each person opped or voiced; for example, /mode channel +vn-ooo nick1 nick2 nick3 nick4 would give voice to nick1 but take away ops from nick2, nick3, and nick4.

Almost all channels you will come across are +tn.