Imported from decentraland/godot-explorer (.claude/skills/mobile-dev-debug-tool/SKILL.md). Install upstream with npx skills add decentraland/godot-explorer --skill mobile-dev-debug-tool. Copyright stays with the author.

Mobile dev debug tool — scene-inspector debug-hub

A single WebSocket channel exposes live client state (scenes / entities / UI / avatars / focus), a log/network/lifecycle stream, and an eval command that runs arbitrary GDScript — reachable on any platform, including iOS/Android devices that can't be dialed into. The client dials out to a desktop debug-hub; local tools (AI / websocat) connect to the hub's consumer port.

There is one transport: the scene-inspector CMD protocol (the source-of-truth contract an external inspector app already parses, so additions stay backward-compatible). eval is hard-disabled in production builds.

Bring up the hub

cargo run -- debug-hub                       # device port 9231, consumer port 9230
# launch the client pointed at the hub's device port (LAN IP shown in the banner):
cargo run -- run -- --scene-inspector=ws://127.0.0.1:9231              # desktop
cargo run -- run --target ios -- --scene-inspector=ws://<this-mac>:9231   # device

On iOS the dcl-ios-devtools export plugin auto-bakes the hub address (debug builds), so even a Godot-editor deploy phones home — just accept the local-network prompt on first launch. The bridge activates at boot (global.gd::_activate_scene_inspector_from_config, from _ready + on every deeplink), so the channel is live from the lobby, before login — no need to enter a world first.

Answering "what state is the app in?" — ONE step

Run the pre-armed connector in the background, read its output, then query:

scripts/hub-connect.sh          # Bash tool: run_in_background: true — read its output

hub-connect.sh does the whole cold-start dance in one shot: wires Android adb reverse, ensures a hub (reuse or start), waits ≤35 s for the device to dial in, and prints either === CONNECTED === + a ping snapshot or a NO DEVICE relaunch hint. If it started the hub it keeps the task alive so the hub persists. Then query with the id-filtered helpers:

scripts/unified.sh scenes
scripts/unified.sh scene '{"scene_id":0,"filters":{"limit":5}}'
scripts/unified.sh eval  'return {"scene": str(get_tree().current_scene.name), "scenes_loaded": Global.scene_runner.debug_get_loaded_scene_ids().size()}'

Why it just works: the client dials out and retries forever (backoff 1s→…→30 s cap, scene_inspector_websocket.gd), and debug builds default the target to ws://127.0.0.1:9231 with no arg (global.gd), so a hub started after the app is picked up within ≤30 s — no app restart needed. Per platform:

• iOS — the dcl-ios-devtools export plugin bakes ws://<LAN-IP>:9231 (even a Godot-editor deploy phones home); accept the Local Network prompt once.
• Android — NO plugin bakes the arg (the baking plugin is iOS-only, and Android editor-deploy CLI args don't reach the app). The debug loopback default + adb reverse tcp:9231 (set by hub-connect.sh) carry it instead. A build made before that default won't connect — rebuild+redeploy, or use cargo run -- run --target android.
• desktop — cargo run -- run -- --scene-inspector=ws://127.0.0.1:9231, or an editor F5 also auto-dials loopback.

If hub-connect.sh reports NO DEVICE, the app simply isn't dialing — follow the hint it prints (usually: relaunch/redeploy the app).

Wiring

• Command backend: DebugWs autoload → godot/src/tool/debug_server/debug_ws_server.gd (run_command) + debug_collector.gd (data assembly). No longer a server — purely the shared inspection/eval backend + keyboard-focus tracker.
• Transport: godot/src/tool/scene_inspector_bridge.gd (drives CMD ↔ ACK and the streams) + godot/src/logic/scene_inspector_websocket.gd; Rust side in lib/src/tools/scene_inspector/. The hub is the debug-hub xtask (src/log_server.rs).
• Rust #[func] hooks for state only Rust can reach:
  • SceneManager::debug_* (lib/src/scene_runner/scene_manager.rs) — CRDT enumeration, deserialization, UI control lookup.
  • AvatarScene::debug_* (lib/src/avatars/avatar_scene.rs) — avatar listing, address/alias/entity/local lookup.

Protocol (scene-inspector CMD)

• request: {"type":"SCENE_INSPECTOR_CMD","cmd":"<verb>","args":{...},"id":"<id>"}
• reply: {"type":"SCENE_INSPECTOR_CMD_ACK","id":"<id>","ok":<bool>,"data":...} (or {"ok":false,"error":"..."})
• streams (push): {"type":"SCENE_INSPECTOR","payload":{"sessionId":...,"entries":[{type:...}]}} where entries[].type ∈ crdt | op_call_start | op_call_end | scene_lifecycle | perf | log | network | session_start | session_end.

The id is echoed in the ACK — always match replies by it (see the perf-vs-ACK note below). The helpers (scripts/unified.sh) do this for you.

Five trees, one command surface

All four data cmds (scene, ui_scene, avatar, app_ui) share a filters dict:

• component: [...] — OR-match SDK component names (cheap, no proto decode)
• property_is: {component, field, contains} — generic substring filter on any (SDK component, field) pair
• collect_nodes: {<child_name>: [<property>, ...]} — per-child-node property dump via Object.get(); values pass through _variant_to_json
• include_parents, include_children, limit, offset, depth, class_filter, name_contains — traversal/pagination knobs

Querying — unified.sh

scripts/unified.sh <cmd> [args-json] sends one CMD frame to the hub consumer port (ws://127.0.0.1:9230) and returns its matching ACK. It bakes in -B 16777216 so websocat doesn't split large replies, and keeps the socket open until the ACK's id matches (needed for on-device round-trips). Requires websocat on $PATH (cargo install websocat or your package manager).

# Confirm the round-trip to the connected client
scripts/unified.sh ping

# All loaded scenes
scripts/unified.sh scenes

# All TextShape entities in scene 0 with their Label3D properties
scripts/unified.sh scene '{"scene_id":0,"filters":{
  "component":["TextShape"],
  "collect_nodes":{"TextShape":["text","font_size","pixel_size","outline_size","modulate"]}
}}'

# Your own avatar — what it's wearing + what's playing
scripts/unified.sh avatar '{"by":"local","filters":{
  "collect_nodes":{"AnimationPlayer":["current_animation","autoplay"],"AnimationTree":["active"]}
}}'

# Explorer's own UI hierarchy (lobby in this state, scene UI when loaded)
scripts/unified.sh app_ui '{"filters":{"depth":2}}'

# Keyboard-focus tracker — current owner + ui_root + change history
scripts/unified.sh focus

Eval — running GDScript

scripts/unified.sh eval '<gdscript>' compiles and runs the snippet against the live client and returns the serialized result — the agent-facing equivalent of a devtools console. Non-production only: in a production build the cmd replies {"ok":false,"error":"eval disabled in production builds"}.

code is a GDScript function body. Use return X to send a value back. Three locals are in scope:

Autoloads (Global, DebugWs, …) and engine singletons (OS, Engine, Time, …) are reachable directly too. A bare single-line expression is auto-wrapped in return, so eval '1 + 1' works without the keyword.

The result passes through the same _variant_to_json used elsewhere (primitives, Vector*, Color, AABB, Array, Dictionary; everything else — Object/Node/Callable — falls back to str()).

# Bare expression (auto-wrapped)
scripts/unified.sh eval 'Engine.get_frames_per_second()'

# Reach into the tree
scripts/unified.sh eval 'return tree.get_root().get_child_count()'

# Multi-line statement body
scripts/unified.sh eval 'var names = []
for c in tree.get_root().get_children():
	names.append(c.name)
return names'

Limitations: synchronous only — await is not supported (it would return a coroutine signal, not the awaited value). GDScript runtime errors (e.g. a null access) are logged to the client console and the eval returns null with ok:true; only compile errors come back as ok:false.

focus — keyboard-focus tracker

focus takes no args and returns the viewport's current keyboard-focus owner plus a timestamped change history (no filters). Reply data: {"current": "<path> [<class>]", "ui_root_path": "/root/explorer/UI", "history": [{"t_ms", "frame", "from", "to"}, ...]} (last FOCUS_HISTORY_MAX = 64 changes; "<none>" means focus was released to null).

DebugWs polls get_viewport().gui_get_focus_owner() every _process frame (in debug builds) so the history captures transient changes — including release-to-null, which the engine's gui_focus_changed signal misses.

Use it for "input stops working" bugs: mobile walk/jump are gated by player.gd → explorer_has_focus() (== ui_root.has_focus()), so movement silently dies whenever current ≠ ui_root_path. The history shows which control stole focus and on which frame. (This is how the navbar-toggle focus-steal bug was found: the gate read true→false when a press landed focus on the navbar's full-rect Button.)

Streams — unified-tail.sh

scripts/unified-tail.sh                 # logs only (default)
scripts/unified-tail.sh log,network     # logs + HTTP
scripts/unified-tail.sh log,lifecycle   # logs + per-tick scene lifecycle

Capture is connection-gated + opt-in. With no consumer connected, the device captures NOTHING (no buffering) — safe to leave the tool enabled in prod. Classic streams (crdt/perf) flow once a consumer connects; log/network/lifecycle are opt-in (the helper subscribes for you). source ∈ rust | godot | native (Swift/ObjC on iOS).

MCP / AI loop: the hub's consumer port (ws://127.0.0.1:9230) is a stable local endpoint an MCP server (or the helpers above, called from Bash) can use to read all logs and issue eval/queries — the same contract the external app uses.

Important notes

• Report state from a request/reply ACK, never from a stray perf frame. On the hub, perf (and crdt) are always-on pushes that start the instant a consumer connects — so a naïve read of the socket returns a perf frame, not the answer to your command. Always query with the id-filtered request/reply (unified.sh <cmd>), which matches the ACK by its unique id. If a query comes back empty, that's a dropped ACK — do not fall back to inferring app state from a perf push (it only happens to carry fps/mem/scene_count; it has no realm/avatar/UI, and its scene_count: 0 can mislead you into "everything's fine / in lobby"). On a device the ACK needs a full consumer→hub→device→hub round-trip, so it lands after the first pushed perf: the helper must keep the socket open until the id matches (unified.sh does this via a trailing sleep that grep -m1 tears down on match). Closing stdin right after sending — as an ad-hoc printf frame | websocat does — drops the ACK on-device.
• The local-player avatar appears in avatars with is_local: true and lives on SceneManager.player_avatar_node, separate from the AvatarScene.avatar_godot_scene HashMap that tracks remote players.
• The entity cmd returns godot.present: false for CRDT entities the renderer hasn't instantiated yet — that's an instantiation throttle in large scenes, not a bug in the tool.
• app_ui skips <root>/SceneUIContainer/scenes_ui by default to avoid shadowing ui_scene; pass include_scene_ui: true to lift the skip.
• The inspection cmds are read-only; only eval can mutate client state.
• Large replies (expanded scene / app_ui) can be huge — narrow filters (add component / property_is, drop include_children/include_parents, use limit) if a reply is unwieldy.
• scene defaults include_children and include_parents to false. Pass them as true explicitly when you want the tree expanded; entity still inlines parents/direct children by default.

Recipes (use cases)

Setup once (export H=.claude/skills/mobile-dev-debug-tool/scripts):

cargo run -- debug-hub                                    # the hub (terminal 1)
cargo run -- run -- --scene-inspector=ws://127.0.0.1:9231 # desktop client -> hub
# iOS device: cargo run -- run --target ios  (export plugin auto-bakes the hub
#   address); then log in + enter a world + accept the local-network prompt.

1. Inspect a scene

$H/unified.sh scenes                                           # loaded scenes (id/title/urn/count)
$H/unified.sh scene  '{"scene_id":0,"filters":{"limit":5}}'    # entities + their components
$H/unified.sh entity '{"scene_id":0,"entity_id":600}'          # one entity + parents/children
$H/unified.sh scene  '{"scene_id":0,"filters":{"component":["MeshRenderer"]}}'  # by component
$H/unified.sh avatars                                          # avatars present
$H/unified.sh avatar '{"by":"local"}'                          # your avatar (position, animations)
$H/unified.sh app_ui '{"filters":{"depth":2}}'                 # the explorer's own UI tree

Component histogram across the scene (via eval): $H/unified.sh eval with a snippet that loops debug_list_entities × debug_get_entity_component_names and tallies — see "Tower of Madness" example in the session notes (Transform/TextShape/GltfContainer counts).

2. See logs

$H/unified-tail.sh log | jq -r 'select(.type=="SCENE_INSPECTOR").payload.entries[]?
                               | select(.type=="log") | "[\(.source)] \(.msg)"'
$H/unified-tail.sh log,network                                 # + HTTP

Logs are opt-in (the helper subscribes for you) and connection-gated — nothing flows without it. source ∈ rust | godot | native (Swift/ObjC on iOS).

3. Follow the app lifecycle via logs

Start tailing BEFORE the action, then trigger it (realm change / jump / re-enter world):

$H/unified-tail.sh log | jq -rc 'select(.type=="SCENE_INSPECTOR").payload.entries[]?
  | select(.type=="log" or .type=="scene_lifecycle")
  | if .type=="log" then "[\(.source)] \(.msg)"
    else "LIFECYCLE \(.event) scene=\(.scene_id)" end'

scene_lifecycle events: scene_init, main_crdt_loaded, script_loaded, on_start, on_update(_end), scene_shutdown. Silence the per-tick on_update firehose with the set_lifecycle_verbose command (args:{"enabled":false}) so boot/load events stay readable.

4. Instrument a feature you're building (add logs + verify)

The dev loop while working ON this branch:

1. Add a log at debug level for your feature:
   • Rust: tracing::debug!("[myfeat] x={:?}", x); — use debug!, NOT info! (info ships to mobile/Sentry-adjacent paths).
   • GDScript: print("[myfeat] ...") — captured as source "godot".
2. Run with debug logging on for your module:

   cargo run -- run -- --scene-inspector=ws://127.0.0.1:9231 --rust-log='dclgodot::yourmod=debug,warn'

   (device: bake --rust-log=... into DCL_IOS_GODOT_CMDLINE next to --scene-inspector=.)
3. Tail just your tag while you exercise the feature:

   $H/unified-tail.sh log | jq -rc 'select(.type=="SCENE_INSPECTOR").payload.entries[]?
     | select(.type=="log" and (.msg|test("myfeat"))) | "[\(.source)] \(.msg)"'

4. Poke it live without redeploying — eval to read state or call your code:

   $H/unified.sh eval 'return Global.your_singleton.your_state'
   $H/unified.sh eval 'Global.your_singleton.trigger(); return "ok"'

   (eval mutates — non-prod only. Ideal for "does my new function actually do X?" with no rebuild.)

Caveats: GDScript print is captured but push_warning/push_error are NOT (only Rust warn/error, via the tracing layer). Mobile's default filter is info, so debug! lines need --rust-log=...=debug. Everything is connection-gated + opt-in, so a prod build with the tool present captures nothing until you connect.