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Debug

Type	Class (static members)
Namespace	`UnityEngine`
Output	Console window, Scene view

Debug

Debug prints messages to the Console and draws lines in the Scene view. It's the quickest way to find out what your code is actually doing.

Static Methods

Method	Description
`Log(object message)`	Print a normal (white) message.
`Log(object message, Object context)`	Same, and clicking the message highlights `context` in the Hierarchy. Pass `this` or `gameObject`.
`LogWarning(object message)`	Yellow warning.
`LogError(object message)`	Red error. Doesn't stop the game.
`LogException(Exception e)`	Log a caught exception with its stack trace.
`DrawLine(start, end, color, duration)`	Draw a line in the Scene view. `duration` in seconds (0 = one frame).
`DrawRay(start, direction, color, duration)`	Draw a line from a point in a direction. The length of `direction` is the length drawn.
`Assert(bool condition, message)`	Logs an error if the condition is false. Removed from release builds.
`Break()`	Pauses the Editor, as if you'd clicked Pause.

Code Samples

Useful logging

// String interpolation ($"...") makes logs readable.
Debug.Log($"{name} took {damage} damage, health now {health}", this);

if (target == null)
{
    Debug.LogWarning($"{name} has no target assigned!", this);
}

Visualize a raycast

Vector3 origin = transform.position;
Vector3 dir = transform.forward * 10f;
bool hit = Physics.Raycast(origin, transform.forward, 10f);
Debug.DrawRay(origin, dir, hit ? Color.green : Color.red);

Gizmos: always-visible helpers in the Scene view

[SerializeField] private float detectRadius = 5f;

void OnDrawGizmosSelected() // only when this object is selected
{
    Gizmos.color = Color.yellow;
    Gizmos.DrawWireSphere(transform.position, detectRadius);
}

What happens at runtime

Debug.Log builds a message, captures a stack trace and sends it to the Console. This is relatively slow, especially with thousands per second.
Logs also run in built games. They go to a log file (Player.log), so leftover logs in Update still cost performance.
Debug.DrawLine/DrawRay only show in the Scene view, or in the Game view when the Gizmos button is on. They do nothing in builds.

Tips

Use Collapse in the Console to group identical messages.
Double-click a message to open your code at that line.
For step-by-step debugging, attach your code editor's debugger (Visual Studio / Rider / VS Code: "Attach to Unity") and set breakpoints. Often faster than adding logs.

Common Mistakes

Logging every frame and leaving it in. Hurts performance, even in builds. Remove it, or wrap it in a condition.
Console shows nothing. Check that the Log/Warning/Error filter buttons (top right of the Console) aren't turned off.

Debug

Static Methods

Code Samples

Useful logging

Visualize a raycast

Gizmos: always-visible helpers in the Scene view

What happens at runtime

Tips

Common Mistakes

See also