roblox-npcs

Official sources (always check these for the latest):

• https://create.roblox.com/docs/en-us/characters/pathfinding
• https://create.roblox.com/docs/en-us/workspace/streaming
• Engine classes: PathfindingService, Path, PathWaypoint, PathfindingModifier, PathfindingLink, Humanoid

This skill covers navigation mesh pathfinding and the AI patterns that use it. It does not cover custom A* implementations unless absolutely necessary — PathfindingService is the official, optimized solution.

When to use this skill

Activate when:

• Building zombies, guards, pets, companions, or any AI that walks/follows/patrols.
• Tuning agent size, jump/climb ability, or preferred terrain.
• Handling dynamic obstacles and blocked paths.
• Using PathfindingModifier regions/links for doors, traps, ladders, boats.
• Scaling pathfinding for many agents.

Cross-reference:

• [roblox-core/SKILL.md](../roblox-core/SKILL.md) for services and Humanoid basics.
• [roblox-networking/SKILL.md](../roblox-networking/SKILL.md) for server-authoritative AI.
• [roblox-physics/SKILL.md](../roblox-physics/SKILL.md) for custom non-humanoid rigs and mover constraints.
• [roblox-testing/SKILL.md](../roblox-testing/SKILL.md) for profiling AI cost.

PathfindingService basics

Create a path:

local PathfindingService = game:GetService("PathfindingService")

local path = PathfindingService:CreatePath({
    AgentRadius = 2,
    AgentHeight = 5,
    AgentCanJump = true,
    AgentCanClimb = false,
    WaypointSpacing = 4,
    Costs = {
        Water = 20,
        DangerZone = math.huge,
    }
})
path.CalculationSecondsTimeout = 1

Compute and follow:

local humanoid = character:WaitForChild("Humanoid")
local rootPart = character:WaitForChild("HumanoidRootPart")

local success, err = pcall(function()
    path:ComputeAsync(rootPart.Position, endPos)
end)

if success and path.Status == Enum.PathStatus.Success then
    local waypoints = path:GetWaypoints()
    -- follow waypoints with Humanoid:Move()
end

Agent parameters

Path.CalculationSecondsTimeout limits how long the solver may run per ComputeAsync call. Set it after CreatePath and before computing.

PathWaypoint actions

Each waypoint has a Position and an Action:

• Enum.PathWaypointAction.Walk — normal movement.
• Enum.PathWaypointAction.Jump — trigger jump.
• Custom labels like "Climb" or "UseBoat" from PathfindingModifiers/Links.

Pathfinding modifiers

PathfindingModifier instances on anchored, non-colliding parts let you influence path cost:

• Label — key used in Costs table.
• PassThrough — if true, the volume is ignored by the navmesh and treated as traversable empty space (e.g., zombies "hearing" through doors).

Example:

local path = PathfindingService:CreatePath({
    Costs = {
        Water = 20,
        DangerZone = math.huge,
        UseBoat = 2,
    }
})

Pathfinding links

PathfindingLink connects two Attachments with a custom label and cost, allowing paths across normally untraversable gaps.

Use for:

• Boats across water
• Teleporters
• Ladders
• One-way jumps

Your movement code checks the waypoint label and runs the custom traversal logic.

Movement patterns

Follow

Continuously recompute a path to a moving target. Throttle recomputation (e.g., every 0.5–1 s) and only recompute if the target moved far enough.

Patrol

Cycle through a list of fixed points. Recompute when blocked.

Chase

Like follow, but validate line-of-sight and distance server-side. Don't trust client-reported positions for authoritative AI.

State machine

Common NPC states: Idle, Patrol, Chase, Attack, Return. Each state handles its own path computation and Humanoid control.

Streaming compatibility

• Server-side scripts have full world state and can compute paths to any part.
• Client-side scripts may fail if the destination has streamed out. Use workspace.PersistentLoaded and persistent models for client path destinations.
• Recompute paths when dynamic/streamed obstacles block the way.

Limitations

• Direct line-of-sight distance ≤ 3,000 studs.
• Computation node budget ≈ 20,000 nodes.
• Waypoint Y coordinate must be between -65,536 and +65,536 studs.
• Incompatible parameters (e.g., AgentCanJump = false to a jump-only destination) will fail.

Performance at scale

• Recompute paths on a staggered schedule, not every frame.
• Share target positions across similar NPCs when possible.
• Use WaypointSpacing = math.huge to reduce intermediate waypoints for long straight runs.
• Consider simplifying agent geometry or using fewer active agents.
• For very large worlds, split into regions or use local patrol paths.

Common mistakes this skill prevents

• Computing paths every frame.
• Ignoring blocked-path events and letting NPCs walk into walls.
• Trusting client position for authoritative AI.
• Forgetting pcall around ComputeAsync.
• Using material names incorrectly in Costs (must match Enum.Material names as strings).

Scripts

• scripts/NPCPathFollower.lua — Humanoid-based path follower with blocked-path recompute, custom-label support, and connection cleanup.
• scripts/PatrolBehavior.lua — state-driven patrol/chase behavior with spatial detection and throttled recomputation.
• scripts/PathfindingUtility.lua — helpers for throttled recomputation and waypoint formatting.

Best practices

• Set Path.CalculationSecondsTimeout after CreatePath to cap solver time.
• Always set an explicit Humanoid:MoveTo timeout and cancel it when the waypoint is reached or the follower is stopped.
• Detect targets with spatial queries such as workspace:GetPartBoundsInRadius instead of scanning every player each frame.
• Stop path followers and clean up Heartbeat connections when the Humanoid dies or the NPC is destroyed.
• For respawning NPCs, create a new behavior instance for the new character model and Destroy the old one.
• Use PathfindingLink labels to trigger custom traversal logic (boats, teleporters, ladders). The follower invokes a registered handler; if none exists, the waypoint falls back to normal movement.
• To enable climbing, set AgentCanClimb = true and provide TrussPart surfaces. Climb waypoints have the Label "Climb".
• PathfindingModifier parts must be Anchored = true and CanCollide = false.

How to proceed

1. Define the agent's size and movement abilities.
2. Build the world with modifiers/links for special regions.
3. Implement a path-follower that handles waypoints, jumps, and blocked events.
4. Layer a state machine for complex behaviors.
5. Run on the server for authoritative AI; use client only for visual prediction.
6. Profile with MicroProfiler and stagger recomputation for many agents.

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Reference index

• [modifiers-links-and-streaming.md](references/modifiers-links-and-streaming.md)
• [npc-behavior-patterns.md](references/npc-behavior-patterns.md)
• [pathfinding-service-details.md](references/pathfinding-service-details.md)
• [performance-and-scaling.md](references/performance-and-scaling.md)

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