An IRC bot is a set of scripts or an independent program that connects to Internet Relay Chat as a client, and so appears to other IRC users as another user. It differs from a regular client in that instead of providing interactive access to IRC for a human user, it performs automated functions.

The historically oldest IRC bots were Bill Wisner’s Bartender and Greg Lindahl’s GM (Game Manager for the Hunt the Wumpus game). Over time, bots evolved to provide special services, such as managing channels on behalf of groups of users, maintaining access lists, and providing access to databases.

Often, an IRC bot is deployed as a detached program running from a stable host. It sits on an IRC channel to keep it open and prevents malicious users from taking over the channel. It can be configured to give channel operator status to privileged users when they join the channel, and can provide a unified channel operator list. Many of these features require that the bot be a channel operator. Thus, most IRC bots are run from computers which have long uptimes (generally running a BSD derivative or Linux) and a fast, stable Internet connection. As IRC has become popular with many dial-up users as well, special services have appeared that offer limited user-level access to a stable Linux server with a decent connection. The user may run an IRC bot from this shell account. These services are commonly known as shell providers.

A bot can also perform many other useful functions, such as logging what happens in an IRC channel, giving out information on demand (very popular in IRC channels dealing with user support), creating statistics, hosting trivia games, and so on. These functions are usually provided by user-writable scripts, often written in a scripting programming language such as Tcl or Perl, added to the bot in question. Channels dedicated to file sharing often use XDCC bots to distribute their files.

IRC bots are particularly well-used on IRC networks without channel registration services like ChanServ, such as EFnet and IRCnet, and on networks that may prevent channels from being registered due to certain registration requirements (minimum user count, etc.), such as Undernet or QuakeNet. Where bots are used for administrative functions such as this, they may need more access than a normal client connection allows. Some versions of IRC have a “Service” protocol that allows clients with these extra powers. Such server-sanctioned bots are called IRC services.

Bots are not always welcome. Some IRC networks forbid the usage of bots. One of the reasons for doing so is that each nickname connected to the network increases the size of the network database which is being kept in sync across all servers. Allowing for bots in large networks can cause a relevant amount of network traffic overhead which needs to be financed and may even lead to netsplits. This however is a shortcoming of the IRC technology, not the bots.

People that create an IRC bot use either the scripting language built into a client, or appropriate frameworks of a suitable programming language to connect to an IRC server(s), or they use an existing bot implementation, and adapt it to their needs.