SecondBrain
by sailex
With SecondBrain installed on a Fabric server, the world gains AI-powered NPCs that chat and act like players, driven by a language model.
What it does
SecondBrain is a Fabric mod that brings intelligent NPCs into the Minecraft world. Each NPC is a player-like character controlled by a large language model: it responds to chat messages and can perform basic player actions. A server operator creates, spawns, despawns, deletes and edits NPCs through an in-game GUI opened with the secondbrain command.
The model backend is set up separately. The author text names a running Ollama server, the Player2 app or an OpenAI key as options. The mod works on the server side, and a client needs it only to talk to the NPCs by voice or text. Files are published for Fabric alone, with the server required and the client optional, so a player can join without it. The mod is open source under the GNU Lesser General Public License v3.0 only, and its source code and issue tracker are public. Snapshot builds are not listed.
Key features
Chat with NPCs
Players write messages in chat or address a specific NPC to start a conversation with it.
Push-to-talk input
Holding the Alt key, or the Option key on macOS, sends speech directly to the language model.
Text-to-speech output
An NPC config screen can turn on text-to-speech so the model's replies are read aloud.
NPC management GUI
The secondbrain command opens a screen where NPCs are created, spawned, despawned, deleted and edited.
Gallery
Compatibility
Latest build for each game version and loader.
Only full game releases are shown. This mod publishes no snapshot builds.
Use cases
Roleplay servers
Server owners can place AI characters in a world that players talk to as they would talk to other players.
Who it’s for: Server owners who want conversational characters, and players who prefer chatting with NPCs over scripted dialogue. Setting up a language model backend is required before the NPCs respond.
How it compares
CraftAgent is a client-side only Fabric mod for 1.21.8, released under the GNU Lesser General Public License v3.0 only, so only the player installs it. Player2 AI NPC runs on Fabric, Forge and NeoForge for 1.20.1 – 1.21.1, with client and server both needed under the MIT License. Viper LLM is server-side only for 1.21 – 26.3 under the MIT License, but it is not open source.
| Mod | Loaders | Game versions | Environment | Updated |
|---|---|---|---|---|
| SecondBrain | Fabric | 1.20.1 – 1.21.11 | Server required, client optional | 2026-04-18 |
| CraftAgent | Fabric | 1.21.8 | Client-side only | 2026-01-06 |
| Player2 AI NPC | Fabric, Forge and NeoForge | 1.20.1 – 1.21.1 | Client and server | 2026-07-19 |
| Viper LLM | Fabric | 1.21 – 26.3 | Server-side only | 2026-09-29 |
Questions
Does SecondBrain need to be installed on the client?
Which language model backends can SecondBrain use?
Which Minecraft versions does SecondBrain support?
In the catalog
SecondBrain is one of 5,392 Social mods on ModsFinder, and one of 4,084 Social mods for Fabric. 19,862 mods support Minecraft 1.21.11.
More from sailex
Similar mods
What the author says
A Fabric mod that brings intelligent NPCs to your minecraft world. Create player-like characters controlled by LLMs that respond to your chat messages and perform basic player actions. This mod works fully serverside. It must also be installed on a client for setup.
Official listing
- Modrinth page
- modrinth.com/mod/secondbrain
- Owner
- sailex
- Published
- 2024-11-08
- Updated on Modrinth
- 2026-04-18
- Facts verified
- 2026-10-15