npc_headcrab is a point entity available in 
Half-Life 2 series and 
Black Mesa.
These are the classic, slow-moving headcrabs. They attack by jumping at the player's head and inflict a nominal amount of damage. Almost any weapon can dispatch them easily.
Commonly found attached to a zombie host body, they will detach if that host is sufficiently damaged below the head.
There are several other headcrab variants and associated zombie types.
See also env_headcrabcanister which is a mortar shell containing a payload of headcrabs. The mortar shell inflicts damage within a radius of where it lands and releases headcrabs after impact. Triggers and entity options offer control over impact damage and when the headcrabs are released, among other options.
Placement Tip:Classic headcrabs can be paired with their fast-moving or poisonous relatives to make it more interesting.Placement Tip:Avoid the cliche of placing headcrabs in vents; they would likely be more of an annoyance than an improvement on gameplay.
Bug:If a headcrab is burrowed, using inputs or command that would kill it like sethealth 0 or npc_kill npc_headcrab does not work. They get ignored and the headcrab's health doesn't change. (tested in: Half-Life 2)Keyvalues
- Name
(targetname) <string>
- The name that other entities refer to this entity by, via Inputs/Outputs or other keyvalues (e.g.
parentname or target).
Also displayed in Hammer's 2D views and Entity Report.
BaseHeadcrab:
- Start burrowed
(startburrowed) <boolean>
- Should this npc start burrowed? Will unburrow via input or if an enemy gets near.
BaseNPC keyvalues
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CBaseCombatCharacter:
- Relationship
(Relationship) <string> !FGD
- <string|targetname or classname> <string|disposition> <int|rank>
- Changes whether this entity likes or dislikes certain other things. Used like the
ai_relationship entity, with this entity as the subject.
- Values for
disposition are:
D_HT: HateD_FR: FearD_LI: LikeD_NU: Neutral
- Physics Impact Damage Scale
(physdamagescale) <float>
- Multiplier for damage amount when this entity is hit by a physics object. With a value of 0 the entity will take no damage from physics.
CAI_BaseNPC:
- Target Path Corner
(target) <targetname>
- The
path_corner that this NPC will move to after spawning.
- Squad Name
(squadname) <string>
- NPCs that are in the same squad (i.e., have matching squad names) will share information about enemies and will take turns attacking and covering each other.
- Hint Group
(hintgroup) <string>
- Hint groups are used by NPCs to restrict their hint-node searching to a subset of the map's hint nodes. Only hint nodes with matching hint group names will be considered by this NPC.
- Hint Limit Nav
(hintlimiting) <boolean>
- Limits NPC to using specified hint group for navigation requests. Does not limit local navigation.
- Sleep State
(sleepstate) <choices>
- Holds the NPC in stasis until specified condition. See also Wake Radius and Wake Squad.
- 0: None
- 1: Waiting for threat
- 2: Waiting for PVS
- 3: Waiting for input, ignore PVS
- 4: Auto PVS
- 5: Auto PVS after PVS
- Wake Radius
(wakeradius) <float>
- Auto-wake if player comes within this distance.
- Wake Squad
(wakesquad) <boolean>
- Wake all of the NPCs squadmates if the NPC is woken.
- Enemy Filter
(enemyfilter) <targetname>
- Filter entity to test targets against.
- Ignore unseen enemies
(ignoreunseenenemies) <boolean>
- Prefers visible enemies, regardless of distance or relationship priority.
DamageFilter:
- Damage Filter
(damagefilter) <targetname>
- Name of the
filter_damage_type entity that controls which entities can damage us.
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Flags
Start hidden : [65536]
Start hanging from ceiling : [131072]
BaseNPC flags
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Wait Till Seen : [1]
- Prevents this NPC from seeing (or being seen) until it enters a player's viewcone.
Gag : [2]
- Won't make IDLE sounds until it's angry.
Fall to ground (unchecked means teleport to ground) : [4]
Drop Healthkit : [8]
- Causes this NPC to drop an
item_healthvial upon dying.
Efficient : [16]
- Don't acquire enemies or avoid obstacles
Wait For Script : [128]
- Forces this NPC to "wait" in an idle state until it finishes playing a
scripted_sequence.
Long Visibility/Shoot : [256]
- By default, increases a NPC's sight range to
6,000 units and allows it to attack from anywhere within that distance.
Fade Corpse : [512]
Think outside PVS : [1024]
- Allows this NPC to run its regular AI outside of any player's PVS.
Template NPC : [2048]
- Marks this NPC as a template for entities like
npc_template_maker. The NPC will not spawn on its own. This is not needed for point_template.
Do Alternate collision for this NPC (player avoidance) : [4096]
 Note:This flag is disabled in   episodic for player companions, because the StartScripting input does this.Don't drop weapons : [8192]
Ignore player push : [16384] (in all games since  )
- Entity won't give way to player.
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Inputs
Burrow !FGD- Burrow. If no burrow points within 512 units, does nothing.
BurrowImmediate !FGD- Burrow immediate.
Unburrow !FGD- Unburrow.
StartHangingFromCeiling- Start hanging from ceiling.
DropFromCeiling- Drop if hanging from ceiling.
BaseNPC inputs
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CAI_BaseNPC:
ActivateSpeedModifier !FGD
DisableSpeedModifier !FGD
Break- Smash into pieces. If this is not possible, disappear.
BecomeRagdoll (in all games since )- Remove itself and instantly become a ragdoll with zero force (just go limp). OnDeath, etc. outputs will NOT be fired.
ForceInteractionWithNPC <string> <string> (in all games since )- Force the NPC to use a dynamic interaction with another NPC. Syntax is <targetname> <dynamic interaction>.
ForgetEntity <targetname>- Clears out the NPC's knowledge of a named entity.
UpdateEnemyMemory (in all games since )- Update (or create) this NPC's memory of of the given entity.
GagEnable
GagDisable- Gagged NPCs won't speak (or moan, caw, etc.) unless made to be a choreographed scene.
HolsterWeapon (in all games since )
UnholsterWeapon (in all games since )- Force the NPC to holster or unholster their weapon. Ignored if the NPC is scripting or if the NPC doesn't use weapons.
HolsterAndDestroyWeapon (in all games since )- Same as
HolsterWeapon, except the weapon is destroyed once it has been concealed.
IgnoreDangerSounds <float>- Ignore danger sounds for the specified number of seconds.
InsideTransition !FGD
OutsideTransition !FGD
SetBodyGroup <integer>- HACK: Sets this NPC's body group (from 0–n).
SetEnemyFilter <string>
SetHealth <integer>- Set the NPC's health.
SetMaxLookDistance <float> (only in  )- Sets the maximum look distance for the NPC. Defaults are 2048 and 6000 for long range NPCs.
SetRelationship <string|targetname or classname> <string|disposition> <int|rank>- Changes whether this NPC likes or dislikes certain others. Used like the
ai_relationship entity, with this NPC as the subject.
- Values for
disposition are:
D_HT: HateD_FR: FearD_LI: LikeD_NU: Neutral
SetSquad <string>- Change the name of this NPC's squad. Leaving the parameter blank will remove the NPC from any existing squad.
StartScripting
StopScripting- Enter/exit scripting state, where NPCs ignore a variety of stimulus that would make them break out of their scripts. They ignore danger sounds, ignore
+Use, don't idle speak or respond to other NPCs' idle speech, and so on.
Wake- Wakes up the NPC if it is sleeping.
CBaseCombatCharacter:
KilledNPC !FGD- Tells the entity it killed something. Despite the name, this can include a player. This input will be automatically sent by the victim when they die.
physdamagescale <float>- Scales damage energy when this character is hit by a physics object. With a value of 0 the NPC will take no damage from physics.
DamageFilter:
SetDamageFilter <string>- Sets the entity to use as damage filter. Pass in an empty string (no parameter) to clear the damage filter.
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Outputs
BaseNPC Outputs
OnDamaged- Fired when this NPC takes damage (
!activator is the damage inflictor).
OnDamagedByPlayer- Fired when this NPC is hurt by a player (
!activator is the attacker or vehicle driver [if friendly fire]).
OnDamagedByPlayerSquad- Fired when this NPC is hurt by a player OR by one of the player's squadmates (
!activator is the attacker or vehicle driver [if friendly fire]).
OnDeath- Fired when this NPC is killed (
!activator is the killer).
OnDenyCommanderUse- Fired when this NPC has refused to join the player's squad.
OnForcedInteractionAborted- Fired when the NPC aborts a forced interaction for some reason (target NPC died, couldn't be pathed to, etc.).
OnForcedInteractionStarted- Fired when the NPC starts a forced interaction.
OnForcedInteractionFinished- "NPCs in actbusies can no longer perform dynamic interactions."
Todo: What does this mean?
OnHalfHealth- Fired when this NPC reaches half of its maximum health.
OnHearCombat- Fired when this NPC hears combat sounds.
OnHearPlayer- Fired when this NPC hears the player.
OnHearWorld- Fired when this NPC hears a sound (other than combat or the player).
OnFoundEnemy <targetname>- Fired when this NPC establishes line of sight to its enemy.
OnLostEnemy- Fired when this NPC loses its enemy. Usually due to the enemy being killed/removed, or because this NPC has selected a newer, more dangerous enemy.
OnLostEnemyLOS- Fired when this NPC loses line of sight to its enemy.
OnFoundPlayer <targetname>- Fired when this NPC establishes line of sight to its enemy, and that enemy is a player.
OnLostPlayer- Fired when this NPC loses its enemy, and that enemy was a player. Usually due to the enemy being killed/removed, or because this NPC has selected a newer, more dangerous enemy.
OnLostPlayerLOS- Fired when this NPC loses line of sight to its enemy, and that enemy is a player.
OnSleep- Fired when this NPC enters a sleep state.
OnWake- Fired when this NPC comes out of a sleep state.
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Dedicated Console Variables
Only in Black Mesa 2012. Requires
this texture to display properly as the texture has been removed.
| Cvar/Command | Parameters or default value | Descriptor | Effect |
|---|
sk_headcrab_health | | int | A headcrab's spawn health. |
sk_headcrab_melee_dmg | | int | Melee damage. |
g_debug_headcrab | | bool | Toggle headcrab debugging. |
sk_headcrab_min_jump_dist | | int | Headcrab min jump distance. Only in Black Mesa 2012. |
sk_headcrab_max_jump_dist | | int | Headcrab max jump distance. Only in Black Mesa 2012. |
sv_headcrab_can_latch_on_player | | bool | Toggles headcrab's ability to attach player's head (if player catches it with head). |
See also
Class hierarchy
