about who and why
About Equilibrium Engine
Equilibrium Engine is an open-source behavioral dynamics engine for RPG NPCs — a way to give game characters believable, in-character behavior that you can inspect, reproduce, and debug, without scripting every reaction by hand.
Instead of a behavior tree that grows forever, an NPC is modelled as a small deterministic dynamical system. Each character carries a handful of internal states — things like anger, fatigue, boredom and resentment — that accumulate, decay, and feed back into one another over time. Events from the world pass through memory filters that weigh them by who acted and the existing relationship state, so the same words land differently coming from a friend or a rival. Visible behavior emerges when a state crosses a threshold — and every decision leaves a traceable reaction you can read back tick by tick.
The framing is borrowed from control theory: feeling-states are leaky integrators, escalation and calm are feedback loops, and the whole system is engineered to stay stable and bit-for-bit deterministic — the same inputs always produce the same life. A language model, if used at all, lives only at the edges (turning text into events, and traces into prose); it never drives the decision loop. The result is control-inspired character behavior: differentiated, cheap to run, and explainable.
The author
Robert Malczyk builds characters the way control engineers build systems — decide the wiring first, let calibration find the numbers, and trust nothing that can't be reproduced. Equilibrium Engine is his standing experiment in explainable, deterministic, believable RPG character behavior, developed in public.
Open source
The engine, its data, calibration, tests and the full evaluation harness are open source under Apache-2.0. Read the design and evidence in the white paper, browse the code on GitHub, or watch the dynamics play out in the trace explorer and the scenarios.