Counter-Strike: Global Offensive/Bot Behavior Trees

In Counter-Strike: Global Offensive, bots can be given a behavior tree to follow. A behavior tree dictates how the bot senses things (vision, hearing, damage sensing), moves, attacks, and does other actions. They can be customized for the Co-op gamemode (with info_enemy_terrorist_spawn) and the Guardian gamemode, and are also used internally for Deathmatch.

Behavior trees were first added to the game on September 16, 2019. Since September 1, 2020, behavior trees can be packed into BSP files

They use Valve's proprietary KeyValues3 format (.kv3), which is a text-based format with somewhat strict syntax. They typically use the bt_ prefix, to signify that file is a Behavior Tree. They are stored in csgo/scripts/ai.

Format

The first line of a .kv3 file is always a header specifying the KV3 version. For CS:GO, use this header:

<!-- kv3 encoding:text:version{e21c7f3c-8a33-41c5-9977-a76d3a32aa0d} format:generic:version{7412167c-06e9-4698-aff2-e63eb59037e7} -->

Examples

Default Deathmatch Behavior Tree

Found in csgo/scripts/ai/bt_default.kv3

<!-- kv3 encoding:text:version{e21c7f3c-8a33-41c5-9977-a76d3a32aa0d} format:generic:version{7412167c-06e9-4698-aff2-e63eb59037e7} -->
{
	config = "scripts/ai/deathmatch/bt_config.kv3"
	root =
	{
		type = "decorator_bot_service"
		memory_to_expire =
		[
			{
				key = "ShortTermAttackMemory"
				time = 0.7
				distance = 0
			},
			{
				key = "LongTermMemory"
				time = 10
				distance = 500
			},
			{
				key = "ShortTermInvestigateMemory"
				time = 3
				distance = 200
			}
		]
		child =
		{
			type = "decorator_buy_service"
			output = "ShouldBuy"
			child =
			{
				type = "parallel"
				children =
				[
					{
						type = "decorator_repeat"
						child =
						{
							type = "parallel"
							children =
							[
								// memorize enemies through vision
								{
									type = "subtree"
									file = "scripts/ai/modules/bt_memorize_enemies_vision.kv3"
									name = "MemorizeEnemiesVision"
								},
								// memorize noises happening right now
								{
									type = "subtree"
									file = "scripts/ai/modules/bt_memorize_noises.kv3"
									name = "MemorizeNoises"
								},
								// record the nearest memorized event to investigate
								{
									type = "subtree"
									file = "scripts/ai/modules/bt_memorize_nearest_investigation.kv3"
									name = "MemorizeNearestInvestigation"
								}
							]
						}
					},
					{
						type = "decorator_repeat"
						child =
						{
							type = "selector"
							children =
							[
								// Buy if we have to
								{
									type = "condition_is_empty"
									input = "ShouldBuy"
									negated = 1
									child =
									{
										// sequencer: evaluate first to last child, in order
										type = "sequencer"
										children =
										[
											{
												type = "action_wait"
												wait_time_min = 3
												wait_time_max = 3
											},
											{
												type = "action_buy"
											},
											{
												type = "decorator_remove_key"
												input = "ShouldBuy"
											}
										]
									}
								},
								// Else: face the damage source if we're taking damage
								{
									type = "decorator_sensor"
									entity_type_filter = "DAMAGE"
									output = "Damage"
									priority = 0
									child =
									{
										type = "condition_is_empty"
										input = "Damage"
										negated = 1
										child =
										{
											type = "action_aim"
											input = "Damage"
											acquire_only = 1
										}
									}
								},
								// Else: attack if we see an enemy
								{
									type = "subtree"
									file = "scripts/ai/modules/bt_attack.kv3"
									name = "Attack"
								},
								{
									type = "subtree"
									file = "scripts/ai/modules/bt_heal_if_needed.kv3"
									name = "HealIfNeeded"
								},
								// Else: investigate the closest memorized event
								{
									type = "subtree"
									file = "scripts/ai/modules/bt_investigate_closest_memorized_event.kv3"
									name = "InvestigateClosestMemorizedEvent"
								},
								// Else: hunt
								{
									// sequencer: evaluate first to last child, in order
									type = "sequencer"
									children =
									[
										{
											type = "action_equip_weapon"
											weapon = "BEST"
										},
										{
											type = "decorator_random_int"
											min = 0
											max = 1
											output = "BombSiteIndex"
											child =
											{
												type = "action_choose_bomb_site_area"
												input = "BombSiteIndex"
												output = "HuntAreas"
											}
										},
										{
											type = "action_choose_team_spawn_area"
											output = "HuntAreas"
										},
										{
											type = "action_choose_random_waypoint"
											input = "HuntAreas"
											output = "TargetHuntArea"
										},
										{
											type = "action_move_to"
											destination = "TargetHuntArea"
											movement_type = "BT_ACTION_MOVETO_RUN"
											route_type = "BT_ACTION_MOVETO_FASTEST_ROUTE"
										}
									]
								}
							]
						}
					}
				]
			}
		}
	}
}