Keep your chat history between game sessions
Saves your chat history in singleplayer for a very very long time. Normally, Minecraft wipes your chat history every single time you leave a world or disconnect. Persistent Chat fixes that. This light-weight mod automatically saves your chat history locally so that when you log back in, your previous messages are right where you left them.
Your chat history is stored safely inside your world folder under /data/chat_history.dat.