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ARENA - Java Package for Simulating Original D&D Combat

This code package provides routines for simulating combat in a tabletop Fantasy Role-Playing Game (FRPG) similar to Original D&D or closely-related games. In most cases, the intent is to output aggregate statistics based on many trials of the game between men and monsters. This package provides only command-line, text output; there are no graphics or visualizations, and generally few options for output regarding individual combats.

For a precompiled JAR executable made from this package, and full JavaDoc pages, visit:

The package currently includes five top-level main applications:

ATHENA -- A master program that can initiate any of the applications below. Used as the main application in the combined JAR distribution.

ARENA -- Simulates a population of fighters, battling for experience and treasure over some amount of time (broadly inspired by Roman arena-style events). Combat can be man vs. man or man vs. monster, including simulated excursions against dungeon random encounters; individual combats can by one-on-one or in groups. Statistics at the end show level-based demographics of the overall surviving population, percent of experience from treasure, and number and ratio of deaths caused by each type of monster in the database.

MONSTER METRICS -- Performs a binary search at each fighter level 1-12 to determine how many fighters represent a matched challenge against each monster in the database (i.e., closest to a 50/50 victory chance); then takes a harmonic mean across all levels to suggest an Equivalent Hit Dice (EHD) value, to be used for balancing and experience purposes. More detail available (per-level values and charts) with command-line switches.

MARSHAL -- Creates random bands of men as encountered in the wilderness (e.g., bandits, brigands, buccaneers, nomads, etc., in numbers 30-300), with leaders of generally appropriate levels. The leaders are generated by simulating their entire combat history in the Arena.

NPC GENERATOR -- A minimalist command-line UI to generate characters of any type as per OED rules. The characters, including thieves, wizards, multiclass elves, etc., are generated by a simulated heuristic, not via the Arena above (i.e., different from the Marshal process). Includes simple magic items, spells for wizards, OED feats, and suggested personalities keyed off alignment. (Depends on Apache PDF Box library, make sure that's on your classpath; current version at

GPJ project files for use with jGRASP are included for each of the applications above. It's easiest to simply use Athena.gpj to build the master program and all the child applications.

Note that at the current time, combat is primarily melee only; no sense of space, location, or movement is simulated. Targets of attacks are determined randomly (as per AD&D DMG p. 63 and 70), with each strike.

While common monster special abilities are modeled, we have not implemented magic-user/wizard spells (so: no mixed PC parties with wizards, nor NPC wizard opponents). One round of special attacks is allowed for monster abilities at the start of combat (e.g., dragon breath, giant boulders, medusa gaze, etc.).

To the extent that the original rules are ambiguous or in need of DM adjudication (as in many cases), the author has attempted to research and interpret the rules such as possible, and uses interpretations as expressed in the Original Edition Delta (OED) House Rules set. In some cases, software switches allow toggling between different modes. See for more information.

Note that the data in the MonsterDatabase file is primarily maintained in a spreadsheet external to this package, MonsterDatabase.ods. Changes to the database should be made there first, and then exported to the CSV file in this software package. See


Models combat in a classic tabletop FRPG (e.g., OD&D).




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