Godot Debugging

Godot Debugging

This skill covers systematic debugging for Godot 4.3+ projects in both GDScript and C#. It covers print techniques, breakpoints, signal tracing, the built-in profiler, scene tree inspection, common error patterns, and a step-by-step debugging checklist.

Related skills: godot-optimization for performance profiling, godot-testing for regression tests after fixes, csharp-signals for C# signal debugging patterns.

1. Print Debugging

GDScript

Godot provides several print functions with different purposes. Choose based on the severity and context of what you are logging.

# print() — general output, space-separated values
print("Player position: ", position)
print("Health: ", health, " / ", max_health)

# print_rich() — BBCode-formatted output in the Output panel
print_rich("[color=yellow]WARNING:[/color] Enemy count exceeded limit: ", enemy_count)
print_rich("[b]State:[/b] [color=green]", current_state, "[/color]")

# push_error() — logs an error with a full stack trace; does NOT stop execution
push_error("save_game: file path is empty")

# push_warning() — logs a warning with stack trace; use for recoverable issues
push_warning("AudioStreamPlayer: bus '%s' not found, using Master" % bus_name)

# print_debug() — only prints in debug builds; stripped from release exports
print_debug("Frame delta: ", delta, " | FPS: ", Engine.get_frames_per_second())

# printerr() — prints to stderr; visible in external terminals and CI logs
printerr("Critical: physics state corrupted at frame ", Engine.get_process_frames())

Formatted output patterns:

# String formatting with % operator
print("Actor [%s] dealt %d damage to [%s]" % [name, damage, target.name])

# String.format() with named placeholders
var msg := "Position: ({x}, {y}) at speed {spd}"
print(msg.format({"x": position.x, "y": position.y, "spd": velocity.length()}))

# Printing arrays and dictionaries — use str() for clean output
var inventory := {"sword": 1, "potion": 3}
print("Inventory: ", str(inventory))

# Conditional verbose logging using a project-level constant or autoload flag
if DebugConfig.verbose_ai:
    print_rich("[color=cyan][AI][/color] ", agent.name, " chose action: ", chosen_action)

// String interpolation
GD.Print($"Actor [{Name}] dealt {damage} damage to [{target.Name}]");

// Printing collections
var inventory = new Godot.Collections.Dictionary { { "sword", 1 }, { "potion", 3 } };
GD.Print("Inventory: ", inventory);

// Conditional verbose logging
if (DebugConfig.VerboseAi)
    GD.PrintRich($"[color=cyan][AI][/color] {agent.Name} chose action: {chosenAction}");

When to use each function:

C#

using Godot;

public partial class Player : CharacterBody3D
{
    public override void _Ready()
    {
        // GD.Print — equivalent to GDScript print()
        GD.Print("Player position: ", Position);

        // GD.PrintRich — BBCode formatted
        GD.PrintRich("[color=yellow]Ready called on[/color] ", Name);

        // GD.PushError — logs error with stack trace
        GD.PushError("_Ready: required child node missing");

        // GD.PushWarning — logs warning with stack trace
        GD.PushWarning("AudioBus not found, falling back to Master");

        // GD.PrintErr — writes to stderr
        GD.PrintErr("Critical failure in _Ready");
    }

    private void HandleDamage(int amount)
    {
        // Formatted string output
        GD.Print($"[{Name}] took {amount} damage. HP: {_health}/{_maxHealth}");
    }
}

2. Breakpoints and the Remote Debugger

Setting Breakpoints

• Click the gutter (left of line numbers) in the Script editor to toggle a breakpoint. A red dot appears.
• Use F9 to toggle a breakpoint on the current line.
• Use breakpoint as a statement in GDScript to trigger a programmatic breakpoint:

func _physics_process(delta: float) -> void:
    if velocity.length() > MAX_SPEED:
        breakpoint  # execution pauses here during debug runs
    move_and_slide()

• In C#, use System.Diagnostics.Debugger.Break() or attach a .NET debugger (e.g. JetBrains Rider or VS Code with the Godot extension).

public override void _PhysicsProcess(double delta)
{
    if (Velocity.Length() > MaxSpeed)
    {
        System.Diagnostics.Debugger.Break(); // pause if .NET debugger is attached
    }
    MoveAndSlide();
}

Using the Built-in Debugger Panel

When execution pauses at a breakpoint, the Debugger panel (bottom of the editor) provides:

• Stack Frames — the full call stack; click a frame to inspect its local variables.
• Locals / Members / Globals — inspect and modify variable values live.
• Step Into (F11) / Step Over (F10) / Step Out (Shift+F11) — navigate execution line by line.
• Continue (F5) — resume execution until the next breakpoint.

Remote Scene Inspector

While a running game is paused or mid-session:

1. Open Debugger > Remote tab in the editor.
2. Click Remote in the Scene panel (top-left toggle next to "Scene") to switch the scene tree to the live view.
3. Click any live node to inspect its current properties in the Inspector.
4. Property changes made here are applied immediately for testing.

Monitors Tab

Debugger > Monitors displays real-time engine metrics:

• FPS / Process time / Physics time — spot performance regressions.
• Video RAM / Object count / Node count — track memory growth.
• Physics 2D/3D collision pairs — identify expensive physics scenes.
• Audio latency — catch audio callback overruns.

Click any monitor name to open its graph. Use the Add button to build custom monitor dashboards.

3. Signal Debugging

Inspect at runtime via node.get_signal_connection_list("signal_name") (returns Array of Dictionary with callable, flags, signal). The most common signal bugs: connecting twice (handler fires twice), forgetting to disconnect on free (warnings + dangling refs), wrong handler signature (silent miss).

See references/signal-tracing.md for the full GDScript and C# inspection helpers and the common-signal-issues catalog (double connect, deferred-free races, lambda capture lifecycle, signal-vs-Callable choice).

4. Common Error Patterns

5. Performance Debugging

The Profiler (Debugger → Profiler) shows per-function self-time and call counts. The Monitors tab tracks frame time, FPS, draw-call count, physics tick budget, memory. Open both during the most demanding gameplay scenario; sort the Profiler by Self time to find culprits. For draw-call bottlenecks, watch Visible/Per frame in the Monitors tab.

See references/performance-debugging.md for Profiler workflow, Monitors tab usage, draw-call bottleneck identification, physics-tick monitoring patterns. See also godot-optimization for fixes once a bottleneck is identified.

6. Scene Tree Debugging

print_tree_pretty() dumps the current scene tree to stdout — the fastest way to confirm a node lives where you think. The Remote tab in the editor shows the live scene tree while the game runs. For @tool nodes, implement _get_configuration_warnings() to surface configuration errors in the editor SceneTree dock.

See references/scene-tree-debugging.md for full examples (print_tree_pretty patterns, node-group debug helpers, _get_configuration_warnings GDScript + C#).

7. Systematic Debugging Method

When prints, breakpoints, and remote inspection don't immediately reveal the bug, fall back to a deliberate process: Reproduce → Isolate → Hypothesis → Trace → Fix → Verify → Add a Test. Each step gates the next; skipping ahead wastes time.

See references/systematic-method.md for the full 7-step method with concrete techniques per step (binary search, minimal repro, regression-test patterns).

8. Implementation Checklist

• Use print_debug() for verbose frame-level output that must not appear in release builds
• Use push_error() / push_warning() (not print()) for invalid state and recoverable problems — they include stack traces
• Set a breakpoint with F9 or the breakpoint statement to pause execution rather than sprinkling prints
• Check signal connections with get_signal_connection_list() before assuming a signal is wired correctly
• Inspect the live scene tree with Scene → Remote during a debug session to verify runtime node state
• Open Debugger → Profiler to measure Self time before optimizing — identify the real bottleneck first
• Watch Debugger → Monitors for growing Object Count or Video RAM that indicate a leak
• Use is_instance_valid() to guard any code that runs after an await in case the node was freed during the wait
• Follow the Reproduce → Isolate → Hypothesize → Trace → Fix → Verify → Test order; do not skip ahead to a fix
• Write a named regression test after fixing a bug so the same failure cannot silently recur