Core & Architecture

Tag & Layer

Tags label GameObjects for script identification (CompareTag); Layers group objects for Physics collisions, Camera culling, and Raycast LayerMasks in Unity.

Imagine...

A Tag is like a name badge — "Player", "Enemy", "Treasure" — so a guard can recognize and react immediately (CompareTag). A Layer is like a zoned floor plan in a building — staff only enter floors they are cleared for (Camera Culling Mask), and rooms decide which rooms may physically interact (Physics Layer Collision Matrix).

The concept in detail

A Tag is a string label on a GameObject (one tag per GO). Prefer gameObject.CompareTag(“Player”) over gameObject.tag == “Player” to avoid string allocations. Built-in tags: Untagged, Respawn, Finish, EditorOnly, MainCamera, Player, GameController.

A Layer is an integer 0–31 (32 layers max). Each Layer is one bit in a LayerMask (32-bit bitmask). Layers drive: (1) Camera Culling Mask — only selected Layers render; (2) Physics Layer Collision Matrix — which Layers collide; (3) Raycasting LayerMask — which Layers a ray can hit.

LayerMask: LayerMask.GetMask(“Enemy”, “NPC”) combines layers. Use ~ to invert (exclude): ~LayerMask.GetMask(“Player”) = every layer except Player.

Good practice: name Layers by role (not object names), created under Edit → Project Settings → Tags and Layers. Examples: Ground, Projectile, Interactable, UI, PostProcess.

Compare: Tag vs Layer

🏷 Tag

Purpose

Identify object type in scripts (CompareTag)

Quantity

Unlimited (string); each GO has exactly 1 tag

Uses

OnTriggerEnter, FindWithTag, script comparisons

Examples

PlayerEnemyTreasure

📚 Layer

Purpose

Group objects for Physics & Camera rendering

Quantity

Max 32 layers (0–7 reserved by Unity), bits 0–31

Uses

Culling Mask, Collision Matrix, Raycast LayerMask

Examples

GroundProjectileUI

Hands-on steps

Create a new Tag/Layer

Edit → Project Settings → Tags and Layers. Add entries to the Tags or Layers list.

Assign on a GameObject

Select the GO in Hierarchy → Inspector → Tag or Layer dropdown at the top.

Configure the Collision Matrix

Edit → Project Settings → Physics → Layer Collision Matrix → uncheck pairs that should not collide.

Set Camera Culling Mask

Select Camera → Inspector → Culling Mask → pick Layers to render (a UI Camera often only renders UI).

Use LayerMask in Raycast

Physics.Raycast(origin, dir, distance, LayerMask.GetMask("Ground")) — only hits Ground.

Interactive simulator

Click a GameObject to select it. Change Tag and Layer. Inspect the Collision Matrix and try a Raycast.

Hierarchy

Select a GameObject

Selected: None|Click a GameObject to edit Tag/Layer

Code example

Basic

Identify objects with Tag inside OnTriggerEnter.

using UnityEngine;

public class TreasureChest : MonoBehaviour
{
  private void OnTriggerEnter(Collider other)
  {
      // CompareTag does not allocate a string — better than ==
      if (other.CompareTag("Player"))
      {
          Debug.Log("Player collected the treasure chest!");
          gameObject.SetActive(false);
      }
  }
}

// Find every Enemy in the scene by Tag
GameObject[] enemies = GameObject.FindGameObjectsWithTag("Enemy");
foreach (var e in enemies) e.GetComponent<EnemyAI>().Alert();

Code example

Advanced

LayerMask in Raycast and changing layer at runtime.

using UnityEngine;

public class PlayerGroundCheck : MonoBehaviour
{
  [SerializeField] private float checkDistance = 0.1f;

  // Build LayerMask from names — cache it, do not rebuild every frame
  private readonly int _groundMask = LayerMask.GetMask("Ground", "Platform");

  public bool IsGrounded =>
      Physics.Raycast(transform.position, Vector3.down, checkDistance, _groundMask);

  void Update()
  {
      if (IsGrounded)
          GetComponent<Rigidbody>().drag = 5f;   // friction while grounded
      else
          GetComponent<Rigidbody>().drag = 0f;   // no drag in the air
  }

  // Change Layer at runtime (e.g. ghost through walls)
  public void SetGhostMode(bool ghost)
  {
      gameObject.layer = LayerMask.NameToLayer(ghost ? "Ghost" : "Player");
  }
}

📌 Quick recap

▸Tag = identify in scripts; Layer = control Physics and Camera
▸Prefer CompareTag() over tag == to avoid GC alloc
▸LayerMask is a bitmask — use GetMask() instead of magic numbers
▸Max 32 layers; uncheck Collision Matrix pairs you do not need

⚠️ Common mistakes

❌ Using gameObject.tag == "Player"
String allocation every call → GC pressure
✅ gameObject.CompareTag("Player")
❌ Hardcoded layer bits: layerMask = 8
Breaks when layer order changes
✅ LayerMask.GetMask("Ground")