Which chat protocol inspired Chris Messina's hashtag idea for Twitter?

The chat protocol that inspired Chris Messina’s hashtag idea for Twitter was Internet Relay Chat, or IRC. IRC had long used the hash symbol to identify channels and organize conversations around a topic.

In August 2007, Messina proposed using the symbol on Twitter to group messages, trends, and events. His idea drew on IRC’s channel structure, although Twitter’s implementation was not identical: a hashtag became searchable metadata embedded in an ordinary post rather than a dedicated chat room.

Twitter initially showed little enthusiasm, and Messina was reportedly told that hashtags were mainly for “nerds.” The idea gained practical value during the 2007 San Diego County fires, when users adopted #sandiegofire to follow updates. Hashtags later spread to Instagram, Facebook, YouTube, Reddit, and other platforms. Jaiku is sometimes mentioned alongside IRC because it also influenced Messina’s thinking, but it was a social-messaging service, not the chat protocol named in this question.