Udon Profiler

An editor-only profiler for VRChat Udon. It hooks the SDK’s editor Udon runtime and records every event execution with timing, nesting, caller/callee edges and extern usage, then shows it in a UI Toolkit window. Nothing in this package ships in a world.

Unity’s built-in profiler only shows Udon as a single UdonBehaviour.ManagedUpdate() block. This one answers: which scripts, which events, who calls whom, which externs, per frame.

Install

Drop the package into Packages/ (Unity 2022.3, com.vrchat.worlds >= 3.7). Open Window > Udon Profiler, enter play mode (ClientSim), and it records.

What it shows

• Stat tiles: Udon ms per frame (average and max over the selected range), events per frame, externs per frame, active behaviours. The colour uses a Quest scale factor (default 4x) so editor numbers are judged against a Quest-sized budget.
• Frame chart: one bar per frame. Click selects a frame, drag selects a range, the wheel scrolls. A dashed line shows the auto-pause threshold.
• Frame timeline: a flame chart of the selected frame in execution order and nesting depth, coloured per script. Click a bar to jump to its row.
• Tree: group by Script, GameObject or Event. Columns: % of Udon time, Total, Self, Calls, Externs, Avg, Max per call, Extern ms, and Delta against a saved baseline. Sort by any column. Double-click a row to select the GameObject.
• Detail pane: for the selected row, its instances, who called it, what it calls (delayed events marked), and its externs by count and time.

Toolbar

• Record / Clear.
• Loop events only: keep only _update, _lateUpdate, _fixedUpdate, _postLateUpdate roots so one-off spikes (_start, player joins) do not dominate the maximum.
• Extern timing: toggle the per-extern timestamps.
• Pause >: stop recording on the first frame above N ms and select it.
• Set baseline / Clear baseline: snapshot the current view; later captures show a signed percentage per row.
• Export CSV.
• Quest x: the budget scale factor.

How it works

Harmony patches applied in the editor only:

• UdonBehaviour.RunProgram(uint): a prefix and finalizer record one sample per event with a timestamp pair. Nested events (one behaviour calling SendCustomEvent on another) form the call tree.
• UdonWrapper.GetExternFunctionDelegate: each extern delegate is wrapped once so extern count and time are attributed to the running event, with nested event time subtracted.
• UdonManager.ScheduleDelayedEvent: delayed events are linked to the event that scheduled them instead of appearing as orphan roots.

Recording keeps a 600-frame ring buffer and allocates nothing on the hot path. Overhead while recording is two timestamps per event plus one per extern. Off the main thread (_onAudioFilterRead) nothing is recorded.

Notes

• Frame numbers are Unity’s Time.frameCount, so they line up with the Unity Profiler.
• Editor timings are Mono; Quest runs IL2CPP on a slower CPU. Use the numbers for ranking and the scale factor for rough budgets, not as absolute device timings.
• If the separate Fast Udon VM package is installed, the footer shows which VM is active. Its fused operations bypass the wrapper, so the extern count drops while it is on; timings stay comparable.

License: MIT.