RunUO

RunUO is a server emulator for Ultima Online that enables custom shard creation. It supports multiple client versions, implements the full game network protocol, and uses a C# scripting system.

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• Complete UO client protocol. RunUO fully implements the Ultima Online network protocol including input and output packet management. This implementation covers initial handshake, combat packets, objects, movement and special skills. The server processes each packet according to original specifications guaranteeing compatibility with official unmodified clients.
• Dynamic C# scripting system. All game content is defined through C# scripts loaded in real time. Administrators can modify behaviors, add objects, creatures, skills or entire systems without stopping the server. The built-in compiler detects changes in source files and automatically recompiles affected scripts.
• Advanced world persistence. The save engine uses multiple serialization strategies to store complete world state. Entity data saves to optimized binary files. The system supports scheduled automatic saves, manual saves through commands and a rotating backup mechanism maintaining sequential backup copies.
• Modular extensible architecture. The server core divides into independent modules handling networking, scripting system, persistence and event scheduler. Each module can be replaced or extended through base class inheritance. This structure allows adding features such as guild systems, custom economy or scheduled events without modifying core code.
• Multi-client version support. RunUO maintains compatibility layers for different Ultima Online client versions from early Renaissance era up to recent patches. The server automatically negotiates client version during connection and adjusts packet transmission according to each version capabilities.
• Skill and combat system. The engine implements all original Ultima Online skills including Anatomy, Magery, Blacksmithy and Carpentry with their success formulas, gain by use and effects. Combat system calculates damage based on stats, resistances, armor, weapons and magical bonuses respecting swing timers and animation types per weapon type.
• Object and container management. The object hierarchy supports nested containers, accumulated weight, dynamic properties and custom events. Each object can have associated scripts defining behavior such as consumable tools, keys opening specific doors, chests with locking systems or scrolls teaching spells.
• Access control and administrative ranks. The account system includes access levels ranging from normal player to server owner. Each level has specific permissions over commands, restricted zones and administrative features. Server commands are protected by these levels and can be assigned granularly to individual accounts.
• Tile mapping and pathfinding. RunUO interprets map files (.map), statics files (.staidx, .statics) and landtiles. The engine calculates routes between two points using A* search algorithms adapted to the game tile grid. NPCs use this system to chase players or flee from combat.
• Event-based timer system. The core manages thousands of timed events simultaneously using a priority queue. Actions such as health regeneration, spell duration, creature respawn intervals or object effects are scheduled as events. The timer uses 100ms ticks for fine adjustments without processor overload.
• Multithreading for critical processing. Intensive operations including pathfinding, world saving or large script processing run on secondary threads. The main network thread maintains responsiveness even during heavy tasks preventing mass disconnections due to latency.
• Faction and war system. The engine includes predefined factions such as Order of Chaos and Order of Law with their own scoring systems, bases, relics and ranks. Administrators can create custom factions, define diplomatic relations between them and schedule active war hours.
• Procedural treasure and loot generation. When opening chests or defeating creatures the system generates rewards based on configurable probability tables. Parameters include gold amount, chance of magical items, armor rarity and probability of unique artifacts. Administrators edit these tables in external XML files.
• Guild and alliance system. Players can form guilds with hierarchical structure including leader, officers and members. Guilds can declare wars against other guilds, form strategic alliances and share a common chat zone. All relationships store in the persistence file and restore upon server startup.

RunUO was created in 2002 by Ryan McAdams and Zac Torkelson. The project started as a response to the need for a stable alternative to early Ultima Online emulators. Over subsequent years the core team included developers such as Mark Sturgill, David Simner and Jeff Lill. The original programming language was C# running on .NET Framework 1.0. Version 2.0 released in 2006 completely rewrote the scripting system. In 2023 version 3.0 was released migrating to .NET 8 and removing obsolete dependencies.

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