Sentinel · Beginner · Tutorial 1 of 3
Build a guard that watches for the player and walks its route when nobody's there — in about fifteen minutes, without writing any code and without the game installed.
Sentinel is a behaviour-tree editor. A behaviour tree is how an NPC decides what to do next: a small diagram, read top to bottom, that the game walks every tick. You build it by dragging nodes; Sentinel exports it as a file the game reads.
You don't need Ascent of Ashes installed for any of this. Sentinel ships templates and drives its own preview, so everything below happens inside the tool.
Save early, and save often. Sentinel currently has no unsaved-changes warning. Close the window with unsaved work and it closes immediately — no prompt, no recovery file, tree gone. This is a known gap in the tool, not something you're doing wrong. Build the habit of pressing Save… before you close anything.
From AshForge Studio, find AshForge Sentinel on the dashboard and press Launch. A welcome panel appears with six numbered steps. Read it — it's short, it's accurate, and it's the map for this whole tutorial. Then press Get started.
You're looking at three regions: the node palette down the left, the canvas in the middle with a single Root node, and the Blackboard on the right. Ignore the Blackboard for now — that's tutorial two.
Building a tree from an empty canvas is a poor first exercise, because the interesting part of a behaviour tree isn't the nodes — it's the order they're tried in. Far easier to read a working one first.
Open the Templates menu in the toolbar. Five options: Aggressive, Defensive, Pack Hunter, Patrol Guard, Elite Combatant. They run roughly in order of complexity, and Patrol Guard is the one to start with — five nodes, one idea.
Click it. The status line under the toolbar confirms: “Loaded the 'Patrol Guard' template — tweak it, then Save or Test in Crucible.”
A Selector tries its children in order and stops at the first one that succeeds. So this guard asks: can I see the player? If yes, the Sequence continues on to Investigate and the Selector is satisfied — it never reaches Patrol. If no, the Sequence fails, and the Selector falls through to Patrol.
That's the one idea worth taking away. Selector means or. Sequence means and. Everything else in Sentinel is built from those two.
| Node type | Succeeds when | Use it for |
|---|---|---|
| Selector | any child succeeds | fallbacks — try this, else that |
| Sequence | every child succeeds | steps that must all happen, in order |
| Parallel | per its policy | doing two things at once |
| Condition | the world says so | gates — CanSeePlayer, HealthLow |
| Action | the behaviour completes | doing — Patrol, Attack, Wait |
Right now the guard investigates the instant it sees anyone. Let's make it hesitate first — a beat of realism, and an excuse to use the palette.
Type wait into the palette's Search nodes… box. Drag + Wait onto the canvas. Then connect it: drag from a node's right-hand slot into another node's left-hand slot. Place Wait between CanSeePlayer and Investigate, inside the Sequence.
Read the tree again. See the player, and pause, and investigate — otherwise patrol. You've just changed an NPC's personality with one node.
Press Save… and give it a name. Do it before you experiment further, and again after any change you'd hate to redo. See the warning at the top: there is no safety net here yet.
Set Agents in the toolbar to 3, then press Test in Crucible. Crucible is the suite's testing lab — it drops live 3D agents into an arena and drives them with your tree.
Watch for the fallback firing. Agents who can't see anyone should patrol; the ones who spot the player should stop, pause for your Wait, then investigate.
Back in Sentinel, the debug bar along the bottom carries Stats, Heatmap and Analytics, plus a timeline scrubber. Stats shows how often each node fired.
A node that fired zero times is the most useful thing on that screen. It means a branch is unreachable, and that is almost always a wiring mistake rather than a design one.
Drag the scrubber to step through the run tick by tick.
Open Info… and set a version. Then Export… writes a versioned .behavior.json — the file the game actually loads. Set the version before you export, not after; it's written into the file.
Next — Intermediate: The Contract. Sentinel describes behaviour rather than running it, and once that lands, the Blackboard, the Decorator and the two version numbers all stop being mysterious. It also explains why CanSeePlayer has no settings.