Internet Relay Chat (IRC): A Comprehensive Guide¶

IRC is a text-based, real-time chat protocol from 1988. It predates the web, it has no owner, and it's still running: thousands of open source projects coordinate on it every day, Twitch's chat is built on it, and you can run a full network on a Raspberry Pi.

This page is the overview. The hands-on companion pages are:

• IRC Command Reference — day-to-day user, channel operator, and services commands
• irssi — the terminal client: config, SASL, TLS, scripts
• UnrealIRCd and Anope — running your own IRC server with services

1. What IRC Is¶

IRC is a client–server chat protocol. You run a client, connect to a server, pick a nickname, and join channels (rooms whose names start with #). Messages you send to a channel are relayed by the server to everyone else in it — hence relay chat. You can also send private messages directly to another nick.

A few properties make IRC different from modern chat platforms:

• It's an open protocol, not a product. Anyone can write a client, a server, or a bot. There is no central company and no account required to connect (on most networks).
• Servers don't store history. If you're not connected, you don't see what was said. (Bouncers and IRCv3 chathistory fix this — see §8.)
• It's line-oriented plain text over TCP. You can speak the protocol by hand with openssl s_client. That makes it trivially scriptable and very cheap to run.
• Identity is weak by default. A nickname is just a string until you register it with network services.

2. A Short History¶

Takeaway from 2021: whoever controls a network's servers controls the network. The freenode collapse is why many projects now keep an official channel list on their own website rather than assuming a network is forever.

3. Architecture¶

Servers, networks, and the spanning tree¶

An IRC network is a set of servers linked into a spanning tree (no loops). Each server knows about every user and channel on the network, and messages are propagated along the tree.

           hub1 ──── hub2
          /    \        \
     leaf-a   leaf-b   leaf-c
      (you)            (your friend)

When a link between servers breaks, the tree splits in two and each side sees the other's users quit at once — a netsplit. When the link is restored, users "rejoin" (a netjoin). The spanning-tree design is the reason IRC networks top out at tens of thousands of users per network rather than millions: every server holds the full state.

Clients, nicks, and hostmasks¶

Every connected user is identified by a hostmask:

nick!user@host
amercer!~amercer@umoswg-D6F9202F.cpe.teksavvy.com

• nick — your display name, changeable at any time
• user — your username/ident (prefixed with ~ if the server couldn't verify it via identd)
• host — your hostname or IP, often cloaked (hashed) by the server for privacy

Bans and operator access are written against hostmasks, so understanding them matters (see the ban notes in the command reference).

Services¶

Classic IRC has no concept of accounts. Services are a special pseudo-server linked to the network that provides bots like:

Common services packages are Anope and Atheme. Libera.Chat runs Atheme; small networks usually run Anope.

Ports¶

4. Speaking the Protocol by Hand¶

IRC is plain text lines ending in \r\n. Connecting manually is the best way to understand it.

openssl s_client -quiet -crlf -connect irc.libera.chat:6697

-crlf makes OpenSSL send \r\n line endings, which servers expect. Then type:

CAP LS 302
NICK amercer_test
USER amercer 0 * :Andrew Mercer
CAP END

What you'll see back (trimmed):

:server CAP * LS :account-notify away-notify extended-join multi-prefix sasl=PLAIN,EXTERNAL ...
:server 001 amercer_test :Welcome to the Libera.Chat Internet Relay Chat Network amercer_test
:server 005 amercer_test CHANTYPES=# PREFIX=(ov)@+ ... :are supported by this server
PING :server

Answer pings or you'll be disconnected:

PONG :server
JOIN #libera
PRIVMSG #libera :hello from a raw socket
QUIT :bye

Anatomy of a message:

:amercer!~amercer@host PRIVMSG #channel :the actual text
│└─────── prefix ────┘ └verb─┘ └target┘ └─ trailing param ─┘

Numeric replies are three-digit codes: 001 welcome, 005 server capabilities (ISUPPORT), 332 topic, 353 names list, 433 nickname in use, 474 banned from channel. The excellent Modern IRC docs list them all.

UnrealIRCd note: Unreal sends a PING cookie before registration completes and won't let you in until you PONG it. Naive "pipe some lines into netcat" bots break on this; use a proper library (e.g. the Rust irc crate) for anything automated.

5. Modes¶

User modes (set on yourself with /mode yournick +x)¶

Channel modes¶

Channel membership prefixes¶

Channel operator ≠ IRC operator. A channel op (@) manages one channel. An IRC operator (/oper) administers the server/network. My old notes conflated the two — you don't need to be an IRC operator to give someone +o in a channel you op.

6. IRCv3: The Modernization Effort¶

IRCv3 is a working group of client and server developers extending IRC without breaking old clients. Everything is negotiated with CAP: the client asks what the server supports and opts in.

Support is uneven: modern servers (Ergo, UnrealIRCd 6, InspIRCd 4, Solanum) and clients (WeeChat, Halloy, Goguma, gamja, The Lounge, senpai) implement a lot; older clients implement little beyond SASL.

7. Is IRC Still Relevant?¶

Short answer: yes, in specific niches — and those niches are healthier than the "IRC is dead" meme suggests.

By the numbers¶

IRC is far smaller than at its 2000s peak. Libera.Chat, the biggest network, typically shows somewhere around 30,000–45,000 concurrent users depending on the source and date (see netsplit.de for live figures). Discord has orders of magnitude more. But user count is the wrong measure for IRC — its users are disproportionately the maintainers and core contributors of the software everyone else runs.

Where it's used today¶

Why people choose it¶

• No vendor lock-in. Clients, servers, and bots are interchangeable. Nobody can pull the rug (and when someone tried, in 2021, the communities just moved).
• Low barrier, low resources. No phone number, no Electron app, no account required to lurk.
• Scriptable. A bot is a socket and a loop.
• Focus. No embeds, no reactions avalanche — just text.
• Public, loggable discussion that suits open projects.

Honest drawbacks¶

• No history by default. Needs a bouncer or IRCv3 chathistory support.
• No end-to-end encryption. TLS protects client↔server only; operators of each server can read traffic. (OTR/IRC-level crypto add-ons exist but are niche.)
• Weak mobile story. Mobile OSes kill idle sockets; you need a bouncer plus a push-capable client (e.g. soju + Goguma).
• Onboarding friction. Nick registration, SASL, and netiquette are a learning curve for newcomers.
• Spam waves. Large networks periodically get hit, which is why many channels are +R (registered users only).

IRC compared¶

When IRC is the right choice: public open-source community chat, lightweight internal ops/alerting chat, a self-hosted homelab chat server, bots and automation, or anywhere you want zero dependency on a company.

When it isn't: you need E2E encryption, rich media, or non-technical users on phones with zero setup.

8. Networks Worth Knowing (2026)¶

freenode still exists, but nearly every major project left in 2021; if older docs (including my own) say chat.freenode.net, read it as irc.libera.chat unless the project explicitly says otherwise. SILC, which shipped in irssi's default config, is effectively dead.

Always check the network's website for current TLS ports — prefer 6697 everywhere it's offered.

9. Clients¶

10. Bouncers: Staying Connected¶

A bouncer (BNC) is an always-on proxy that stays connected to IRC for you and replays what you missed when you reconnect. It solves IRC's two biggest usability problems: history and multi-device.

The old pattern of "irssi in screen + screen_away.pl + awayproxy.pl emailing me messages" is now better served by soju + any client. Running irssi in tmux on a server is still perfectly valid if you only ever use a terminal.

11. Security and Privacy¶

1. Always use TLS (port 6697) with certificate verification. Plaintext 6667 exposes your NickServ password and every message.
2. Authenticate with SASL, not /msg NickServ IDENTIFY. SASL logs you in before you join anything, so your cloak is applied before your real host leaks into channels.
3. Prefer SASL EXTERNAL (CertFP). Authenticate with a client TLS certificate instead of storing a password in your client config. See irssi → CertFP.
4. Use a cloak. Most networks cloak your host automatically or on request (+x, or a project cloak like user/amercer on Libera).
5. Don't accept DCC from strangers. DCC SEND/CHAT open direct connections and reveal your IP.
6. CTCP VERSION reveals your client and version; some clients let you blank it.
7. Assume channels are logged. Public channels on FOSS networks are often published on the web.
8. Never paste commands strangers give you. "Type /exec ..." is an old trick.
9. VPN/Tor policies vary. Libera.Chat blocks VPN and Tor connections for users without a registered account; register first, then connect via SASL.

12. Etiquette (the parts that still matter)¶

• Don't ask to ask. Just ask your question, with details.
• Wait. People are in different timezones and idle for hours. Answers can take a while; stay connected.
• Use a pastebin for anything longer than ~3 lines (most project channels name a preferred one in the topic).
• Read the topic — it usually contains rules, links, and current status.
• Don't highlight people unnecessarily, and don't private-message project members for support unless invited.
• Plain text only. No colour spam, no ALL CAPS.
• Lurking is normal and fine.

13. Running Your Own Network¶

Two sensible homelab designs:

Classic: UnrealIRCd 6 + Anope + soju. Most flexible, most to configure. Full walkthrough: UnrealIRCd and Anope.

All-in-one: Ergo alone gives you an IRCd, NickServ/ChanServ equivalents, SASL, and server-side history with a single YAML config and container image. For a personal or small-team server this is the least-effort route. A minimal Compose service following the homelab conventions (network name only in .env):

services:
  ergo:
    image: ghcr.io/ergochat/ergo:stable
    container_name: ergo
    restart: unless-stopped
    ports:
      - "6697:6697"
    volumes:
      - ergo-data:/ircd
    networks: [default]

volumes:
  ergo-data:

networks:
  default:
    name: ${NETWORK}
    external: true

Edit the generated ircd.yaml in the volume to set the server name, TLS certificate paths, and operator password before exposing it.

14. Bots and Automation¶

IRC is still one of the easiest targets for notifications:

• CI/CD notifications — GitLab's Irker integration, or a few lines in a pipeline job pushing to a small bot.
• Monitoring alerts — Alertmanager → webhook → IRC relay bot.
• Meeting bots — MeetBot/Limnoria produce minutes for FOSS project meetings.
• Frameworks — Limnoria (Python), Sopel (Python), or the Rust irc crate for a bespoke tool.

Rules of the road for bots: register the bot's nick, authenticate with SASL, respect flood limits (one line every ~2 seconds is a safe default), and ask channel ops before adding one.

15. Further Reading¶

• Modern IRC Client Protocol — the practical, up-to-date protocol reference
• IRCv3 specifications
• RFC 1459, 2810–2813, 7194
• Libera.Chat guides — registration, SASL, cloaks, CertFP
• netsplit.de — network statistics
• UnrealIRCd documentation
• irssi documentation