War Diary is a real-time strategy game which uses the 16th century Korea as background. There two rival armies fight about the supremacy. The economic system is based on three resources - food, wood and metal - which are used to construct buildings or troops. These can also be purchased with money which can be earned by selling spare resources.

The center of the base is the city hall which sets the radius where the eleven other buildings can be build. Important for the fighting aspect of the game are the barracks where soldiers are trained and the weapon factory where the soldiers are equipped. This means every soldier has to be sent to the weapon factory when he is trained as one of the three available jobs: Shooter, melee fighter or artillery.

When equipping the soldiers there are different quality settings for the weapons which effects costs and effectivity. Weapons degrade and have to be replaced regularly. Troops can be distributed into different groups but the health and weapon durability has to checked for every soldier separately. Other units are watch towers, ships and monks. Monks are used to support the regular troops or to invoke ghosts. Troops and watch towers gain combat experience when fighting the enemy and as a result improve their abilities.