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How do you debug AI behavior in Unreal Engine?

An enemy should chase the player but stands still. The Behavior Tree, Blackboard and perception are configured and the Output Log shows no errors. You open the Gameplay Debugger in play and read the overlay categories:

[Behavior Tree]  active node: MoveTo  -> status: In Progress (never changes)
[Blackboard]     TargetActor = BP_Player  (Set, points at the player)
[Perception]     player is sensed (sight stimulus active)
[Navigation]     no green NavMesh rendered under the bot's spawn area

Diagnose the cause.

Press the apostrophe key in play to open the AI Debugger (Gameplay Debugger): it overlays the active Behavior Tree path, live Blackboard values, perception cones, NavMesh, and the EQS query. Categories toggle on the numpad to isolate the failing system.

✗Not knowing the apostrophe key opens the Gameplay Debugger live
✗Relying on logs alone instead of the visual Behavior Tree overlay
✗Forgetting to check the NavMesh (P key) when MoveTo silently fails

→How do you use the standalone Behavior Tree visual debugger to replay a session?
→What does the Visual Logger add beyond the live Gameplay Debugger?

Contents

Scenario

An enemy should chase the player but just stands still. The Behavior Tree, Blackboard and perception are all set up, and there are no log errors. Where do you look?

Diagnosis — the AI Debugger

In play mode, aim at the bot and press ' (apostrophe). An overlay opens:

[1] Navigation   — shows the NavMesh and the current path
[2] Behavior Tree — highlights the active node
[3] Blackboard    — live key values
[4] Perception    — sight/hearing cones and stimuli

Enable the Behavior Tree category: the active node is frozen on MoveTo with status In Progress and never changes. Switch to Blackboard — the TargetActor key really is Set and points to the player. So the logic is correct.

Enable Navigation: there is no green NavMesh under the bot. No path can be built — MoveTo hangs in In Progress forever, never succeeding and never failing.

Cause

The NavMeshBoundsVolume does not cover the bot's spawn area. Without a NavMesh, MoveTo cannot build a path and the Behavior Tree gets stuck on that task.

Fix

Extend the NavMeshBoundsVolume over the whole playable area and press P to verify — green coverage should appear under the bot. After the navigation rebuild, the chase works.