S&box Gamemode Development Skill
This skill teaches you how to develop gamemodes in S&box (Facepunch's game engine on Source 2).
When to Use This Skill
- •Learning S&box game development from scratch
- •Building a new gamemode or game feature
- •Debugging multiplayer/networking issues
- •Understanding component lifecycle and patterns
- •Avoiding common pitfalls in S&box development
Core Concepts
Component Architecture
S&box uses a Unity/Godot-like component system. All game behavior lives in Components:
public sealed class MyComponent : Component
{
[Property] public float Speed { get; set; } = 100f; // Exposed in editor
[RequireComponent] Rigidbody Body { get; set; } // Auto-linked
protected override void OnStart() { } // First enable
protected override void OnUpdate() { } // Every frame
protected override void OnFixedUpdate() { } // Physics tick (50/sec)
}
Lifecycle order: OnLoad → OnAwake → OnStart → OnUpdate/OnFixedUpdate → OnDestroy
Input Handling
Define actions in ProjectSettings/Input.config, then query them:
if (Input.Pressed("Jump")) // Just pressed this frame
if (Input.Down("Attack1")) // Held down
if (Input.Released("Reload")) // Just released
Vector3 move = Input.AnalogMove; // WASD or left stick
Angles look = Input.AnalogLook; // Mouse or right stick
Networking Fundamentals
Player Spawning (on host):
public sealed class GameManager : Component, Component.INetworkListener
{
[Property] public GameObject PlayerPrefab { get; set; }
public void OnActive(Connection connection)
{
var player = PlayerPrefab.Clone(SpawnPosition);
player.NetworkSpawn(connection); // Assign ownership
}
}
Proxy Check (critical for input):
protected override void OnUpdate()
{
if (IsProxy) return; // Don't process input for other players!
// Your input handling here
}
RPC Broadcasting:
[Rpc.Broadcast]
public void OnDamaged(float amount)
{
// Runs on ALL clients
PlayHitSound();
}
Physics & Raycasting
var tr = Scene.Trace
.Ray(startPos, endPos)
.WithCollisionRules("bullet")
.UseHitboxes(true)
.Run();
if (tr.Hit)
{
Log.Info($"Hit {tr.GameObject} at {tr.HitPosition}");
}
UI with Razor
Create .razor files for UI panels:
@inherits PanelComponent
<root>
<div class="hud">
<label>Health: @Health</label>
</div>
</root>
@code {
[Property] public int Health { get; set; }
}
Common Pitfalls & Blindspots
1. Forgetting IsProxy Check
Problem: Input code runs for all players, causing chaos.
Solution: Always check if (IsProxy) return; at the start of OnUpdate.
2. Not Calling NetworkSpawn()
Problem: Cloned objects don't appear on other clients.
Solution: Always call go.NetworkSpawn() after cloning networked prefabs.
3. Using OnUpdate for Physics
Problem: Frame-rate dependent physics behavior.
Solution: Use OnFixedUpdate for movement, forces, and physics logic.
4. Missing [Property] Attribute
Problem: Fields don't appear in the S&box editor.
Solution: Add [Property] to expose fields in the inspector.
5. Null Reference on Components
Problem: GetComponent<T>() returns null.
Solution: Use [RequireComponent] for guaranteed references, or check for null.
6. Scene References Breaking
Problem: References to scene objects become null after scene reload.
Solution: Use [Property] references or find objects dynamically.
7. RPC Not Calling
Problem: [Rpc.Broadcast] method doesn't execute on clients.
Solution: Ensure the method is on a networked GameObject and ownership is correct.
Debugging Tips
Log.Info("Debug message"); // Console output
Log.Warning("Something weird"); // Yellow warning
Log.Error("Something broke!"); // Red error
// Console commands
[ConCmd("debug_health")]
static void DebugHealth(int amount)
{
Log.Info($"Setting health to {amount}");
}
Log files: <sbox-install>/logs/Log.log
Project Structure Best Practices
Code/ ├── Components/ # Reusable components │ ├── Player/ # Player-related │ └── Weapons/ # Weapon systems ├── GameModes/ # Gamemode-specific logic ├── UI/ # Razor panels └── Managers/ # Singleton managers Assets/ ├── prefabs/ # Prefab GameObjects ├── scenes/ # Scene files └── ui/ # UI assets
Quick Reference
| Task | Code |
|---|---|
| Create GameObject | var go = new GameObject(); |
| Clone prefab | var go = Prefab.Clone(position); |
| Get component | var c = go.Components.Get<T>(); |
| Find in scene | Scene.GetAllComponents<T>() |
| Network spawn | go.NetworkSpawn(connection); |
| Check ownership | if (IsProxy) return; |
| Raycast | Scene.Trace.Ray(start, end).Run() |
API References
- •Docs: https://docs.facepunch.com/s/sbox-dev
- •API Reference: https://sbox.game/api
- •GitHub Issues: https://github.com/Facepunch/sbox-issues