The file consists of a description of combat parameters for the player and all NPC classes in the game. Descriptions are separated from one another with an empty line. Each description consists of the (unique) name of the class and settings. Below is a list of parameters in alphabetical order, which is how they are always written in the file. "string" means that the value should be text; "N" indicates a numeric value; and "mixed" can be either.

There seems to be a mismatch between some of the string values used and what the engine actually looks for. Potentially incorrect values are indicated with a (*).

[Class Name]

This option must be specified first. For example, [Enclave Patrol], [Fighting Mantis] or [Arroyo Villager]. The player is the class named Player AI. Every party member must have the following classes:

[PARTY NAME BERSERK] 
[PARTY NAME AGGRESSIVE] 
[PARTY NAME DEFENSIVE]
[PARTY NAME COWARD] 
[PARTY NAME CUSTOM] 

Here NAME is the name of a member of the team, such as: DOC, LENNY, GORIS, etc.

NOTE: The combat ai-mode types for party members must always be in the above shown order, and the character must always start out in the CUSTOM-mode, otherwise the game will not be able to correctly detect the set ai-mode.

aggression = N

The chance of aggressive behavior by the NPC in combat. Measured as a percentage. Valid values are: 0-100.

area_attack_mode = string

Conditions for burst-fire. Existing values, the internal numeric representation, and the text used for setting custom behavior in-game:

no_pref*               -1  "Not Applicable."
always                  0  "Always!"
sometimes               1  "Sometimes, don't worry about hitting me"
be_sure                 2  "Be sure you won't hit me"
be_careful              3  "Be careful not to hit me"
be_absolutely_sure      4  "Be absolutely sure you won't hit me"

'no_pref' is used by Cyberdog and Goris, and has a line in custom.msg, but is not checked for by the engine.

For party members, these options must be defined in the party.txt file.

combat float

attack_end = N attack_start = N Combat floats said when attacking. At the beginning of the attack, a random number between the two values is chosen. Then the appropriate line number from master.dat/text/english/game/combatai.msg is displayed.

attack_who = string

Who the NPC should attack. Existing values:

whomever_attacking_me     0  "Whomever is attacking me"
strongest                 1  "The strongest"
weakest                   2  "The weakest"
whomever                  3  "Whomever you want"
closest                   4  "Whomever is closest"

For party members, these options must be defined in the party.txt file.

best_weapon = string

Preferred weapon types. This option does not exist for all NPCs. Available values:

no_pref               0  "None"
melee                 1  "Melee"
melee_over_ranged     2  "Melee then ranged"
ranged_over_melee     3  "Ranged then melee"
ranged                4  "Ranged"
unarmed               5  "Unarmed"
unarmed_over_thrown   ? (Spore Plant)
random                ?
never*                ?  (Deathclaw) 

For party members, these options must be defined in the party.txt file.

body_type = string

Defines the block of messages that critters say in response to being hit. The blocks are from master.dat/data/AIBDYMSG.TXT, which in turn refers to lines in combatai.msg . Existing values (examples of critters that use them in parens):

None 
Primitive 
Wimpy Person (Whimpy, Coward ...) 
Punk (SF) 
Berserk Person (Kamakazi. ..) 
Tough Person (Bounty Hunter, Caravan Driver ...) 
Boxer 
Normal Person 
Robot 
Junkie (Crazy Addict) 
Elron (Habologisty) 
Ghoul 
Kaga 
Raider (Khan) 
Raider (Non-Khan) 
Gangster (Mobsters) 
Shi 
Super Mutant (Master Army) 
Goris 
Miron 
Marcus 
Lenny 
Cassidy 
Robo Brain (Hum / Cyb) 
Sulik

called_freq = N

Sets the probability of using an aimed attack, which is calculated as 1/N. Cannot be zero.

chance = N

The likelihood of any message. Measured as a percentage. Valid values are: 0-100.

chem_primary_desire = N

Preference for drug use. PIDs of items, or -1 if there is no preference. If you want to specify multiple types of drugs, they are listed separated by commas (e.g., 284,81,103). Strangely, most critters use 81 (Iguana-on-a-stick, whole).

chem_use = string

NPC drug use in combat. Existing values:

clean                      0  "I'm clean"
stims_when_hurt_little     1  "Stimpacks when hurt a bit"
stims_when_hurt_lots       2  "Stimpacks when hurt a lot"
sometimes                  3  "Any drug some of the time"
anytime                    4  "Any drug any time"
always                     ?

For party members, these options must be defined in the party.txt file.

color = N

Perhaps the font color used for combat floats. It is 58 for all critter types.

disposition = mixed

Determines NPC behavior during a battle. Existing values:

-1* 
none 
custom
coward 
defensive 
aggressive 
berserk

distance = string

The distance between the NPC and its enemy, managing battle tactics. Existing values:

stay_close        0  "Stay close to me"
charge            1  "Charge!"
snipe             2  "Snipe the enemy"
on_your_own       3  "On your own"
stay              4  "Stay where you are"
random*           ?  (listed only for Mobsters and Tough Khan) 

For party members, these options must be defined in the party.txt file.

font = N

Perhaps, the font used for combat floats. Value in the US version of the game is 101. In other versions 102, 103, and 104 are used.

general_type = string

Defines the block of combat taunts that the critter periodically shouts during a battle (attack, retreat, miss). The blocks are in master.dat/data/AIGENMSG.TXT, and refer to lines in combatai.msg . Existing values:

Badger 
Berserk Person 
Bounty Hunter 
Boxer 
Cassidy 
Chip 
Crazed Robot 
Cyberdog
Dragon (The) 
Elron Guards 
Gangster 
Ghoul 
Goris 
Guard (Normal) 
Guard (Tough) 
Junkie 
Kaga (1) 
Lenny 
Lo Pan 
Marcus 
Myron 
None 
Normal Person 
OZ - 7 
OZ - 9 
Primitive 
Raider 
Raider Captain 
Raider Mercs 
Rat God 
Robot 
Ryan 
Shi Guards 
Sulik 
Super Mutant (Master Army) 
The Brain 
Tough Person 
Wimpy Person 

hit_eyes_end = N

hit_eyes_start = N

hit_groin_end = N

hit_groin_start = N

hit_head_end = N

hit_head_start = N

hit_left_arm_end = N

hit_left_arm_start = N

hit_left_leg_end = N

hit_left_leg_start = N

hit_right_arm_end = N

hit_right_arm_start = N

hit_right_leg_end = N

hit_right_leg_start = N

hit_torso_end = N

hit_torso_start = N

NPC messages when hit in the eyes, groin, head, left arm, left leg, right arm, right leg and torso, respectively. For details, see the description of attack_end.

hurt_too_much = string

Indicates the condition in which the NPC starts running away. Multiple conditions are separated by commas.

blind          40
crippled       3c
crippled_arms  30
crippled_legs  0c

'crippled' is equivalent to 'crippled_arms, crippled_legs'

For party members, these options must be defined in the party.txt file.

max_dist = N

The maximum distance from the player where the NPC is hostile. Measured in hexes.

min_hp = N

The minimum number of hit points, at which the NPC starts running away.

min_to_hit = N

The NPC will attack only if it has at least this high a chance (percentage) of hitting its target.

miss_end = N

miss_start = N

NPC combat taunts when missing a target. For details, see the description of attack_end.

move_end = N

move_start = N

Combat taunts used when moving to attack (i.e., when not yet in range of the enemy, but already hostile) For details, see description of attack_end.

outline_color = N

Maybe the color used for target highlighting. For all NPC classes, it is 55.

packet_num = N

Number of the AI package. Never change it! If the new AI package you indicate packet_num, which already exists, then when you click on the AI button in the Mapper (in critter properties), it closes the window. When you create a new AI package, the value of packet_num must be consecutive. In AI.TXT there are 187 values for packet_num, from 0 to 186 inclusive. If you want to add a new package, it should have packet_num 187, the next added package 188, and so on. If packet_num is not followed consecutively, for example, 188 immediately after 186, the mapper will close.

run_away_mode = string

Condition when the NPC will run away. Existing values (second column is minimum amount of damage taken, as a percentage of max HP):

coward              0%   0  "Abject coward"
finger_hurts       25%   1  "Your finger hurts"
bleeding           40%   2  "You're bleeding a bit"
not_feeling_good   60%   3  "Not feeling good"
tourniquet         75%   4  "You need a tourniquet"
never             100%   5  "Never!"
none                0%   6  "None"

For party members, these options must be defined in the party.txt file.

run_end = N

run_start = N

Combat floats used when running away. For details, see the description of attack_end.

secondary_freq = N

Similar to called_freq. Sets the probability of using a secondary (i.e., burst) attack mode, which is calculated as 1/N. Cannot be zero. Only used when area_attack_mode is 'sometimes' or 'no_pref'.

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History

2019-12-15 - Updated information about party members.
2019-12-14 - Ported from https://falloutmods.fandom.com/wiki/AI.TXT_File_Format by ghost
2007 - Translated by Kanhef
1999-12-27 - Written by Serge of Team-X (ai_txt_format.htm)