RPG Engine

An LLM-powered RPG simulator inspired by In Nomine, with a deterministic rules engine, supernatural systems, and a web UI. Play as an angel or demon in a modern city, or as a sellsword in a medieval town.

The LLM describes. The database decides.

Unlike chat-wrapper RPG tools, this engine resolves all mechanics in Python before the LLM writes a single word of narration. The story always matches the dice.

Quick Start

# Requires Python 3.7+, Flask, and Ollama with gemma3:12b
ollama pull gemma3:12b
pip install requests flask

# Modern-day celestial campaign (In Nomine)
python web_ui.py --city

# Medieval fantasy campaign
python web_ui.py

Then open http://localhost:5000 in your browser.

Two Scenarios

Harbor City (--city) — In Nomine Celestial Campaign

Play as a Malakite of War — an angel in a human vessel, investigating demonic activity in a modern city. Full supernatural systems active.

• 17 locations across 4 districts: Downtown, Waterfront, Midtown, Eastside
• 9 NPCs: 3 angels (surgeon, detective, ancient librarian), 2 demons (nightclub owner, information broker), 4 humans (cop, priest, bartender, nurse)
• Songs: 5 supernatural abilities × 3 realms each (Healing, Thunder, Shields, Motion, Tongues) — costs Essence, generates Disturbance
• Disturbance: use a Song and every celestial in the neighborhood might detect you
• Dissonance: act against your angelic nature and accumulate moral corruption — enough triggers permanent Discord flaws
• The War: a demon is building a Tether to Hell in a warehouse. An ancient angel watches and does nothing. A human detective is getting too close to the truth. Your move.

Millhaven — Medieval Fantasy Campaign

A wandering sellsword in a small farming town with intertwined plot threads.

• 15 locations: tavern, market, temple, gates, forest, bandit camp, and more
• 7 NPCs with goals, secrets, and dispositions
• 10 world facts (4 public, 6 secret): missing mayor, weapon smuggling, poisoned well, planned bandit raid

How It Works

Player Input
  → Pass 1: LLM determines mechanical actions (structured, no prose)
  → Validator: checks entity existence, location, dead NPCs
  → Plausibility: LLM judges AUTO / CHECK / IMPOSSIBLE
  → Rules Engine: d666 dice, damage, armor, movement
  → Pass 2: LLM narrates grounded in mechanical results
Player sees narrative + mechanical truth

Features

Core Engine

• d666 resolution: 2d6 vs target number, 3rd d6 = check digit (degree of success). 111 = Divine Intervention, 666 = Infernal Intervention.
• Six stats: Strength, Agility (Corporeal) / Intelligence, Precision (Ethereal) / Will, Perception (Celestial)
• Weapons and armor: base damage + check digit - armor absorption, slashing/piercing/bludgeoning types
• Morale: NPCs flee based on Will checks when HP drops below their threshold
• Economy: silver currency, buy/sell with merchants
• Encumbrance: weight tracking against Strength-derived capacity
• Survival: hunger, thirst, fatigue counters with stat penalties
• Plausibility engine: whitelist for common actions, LLM only consulted for ambiguous cases
• Anti-hallucination: validator rejects invented NPCs, dead targets, impossible movement, items not in inventory

Supernatural Systems (Harbor City)

• Songs: 5 Songs × 3 realms, d666 resolution, Essence cost, 13 effect handlers (heal, damage, shields, telekinesis, truth compulsion, and more)
• Disturbance: BFS location graph traversal, Perception-based detection with distance penalty — use Songs carelessly and every celestial nearby knows
• Dissonance: 7 Angel Choirs and 7 Demon Bands each with unique moral triggers. Seraphim can't lie. Mercurians can't harm humans. Calabim must destroy. Accumulates into permanent Discord flaws.
• Forces, Essence, Vessels, Roles: full celestial character model with cover identities and power levels

Web UI

• Dark-themed three-panel layout: character sheet, narrative center, NPC cards
• Essence bar, Nature badge, Songs list, Dissonance counter (all hidden for mundane characters)
• Clickable exits, swipe to re-roll narration, color-coded mechanics
• NPC cards with goals, knowledge, disposition, and HP

Two-Tier Release

• lore_config.py: all setting terminology in one file. Swap it to rename everything for a commercial release with zero code changes.

Architecture

See rpg-engine-architecture.md for the full design document.

Terminal Mode

The original terminal interface is still available for Millhaven:

python game.py

Commands: look, inventory, status, loot, debug, quit. Anything else is a player action.

Lineage

Built on patterns from:

• Spine Reborn: Validator pattern (propose → validate → commit)
• Sovereignty: Persistent world state integrity
• MinionAI: Deterministic logic over LLM decisions
• LLM Profiler: Know your model's strengths and weaknesses

Legal

In Nomine is a trademark of Steve Jackson Games. This is an unofficial fan project, not affiliated with or endorsed by Steve Jackson Games. Game mechanics are not copyrightable; setting terminology is used under fair use for a free, non-commercial fan work.

License

MIT