Unity Netcode Design Agent Skill

Netcode for GameObjects - Design Rules

Advisory module. Every rule is distilled from com.unity.netcode.gameobjects 2.x source. Each rule cites a concrete file/line so the reasoning is auditable.

> Mode: Documentation only — no REST skills to gate; load freely under any operating mode (Approval / Auto / Bypass).

When to Load This Module

Load before writing or reviewing any of:

• NetworkBehaviour scripts (OnNetworkSpawn / OnNetworkDespawn / RPCs / NetworkVariables)
• NetworkManager startup / shutdown / scene switching
• NetworkObject Spawn / Despawn / ChangeOwnership / TrySetParent
• UnityTransport configuration (direct connect / Relay)
• Any code that branches on IsHost / IsServer / IsClient / IsOwner

Critical Rule Summary (memorize even if you skip the sub-docs)

| # | Rule | Source anchor |

|---|------|---------------|

| 1 | Spawn() / Despawn() must be called on Server/Host only; client-side calls fail. | Runtime/Core/NetworkObject.cs:1884, 1921 |

| 2 | OnNetworkSpawn() runs before Unity Start() and after Awake/OnEnable. | Runtime/Core/NetworkBehaviour.cs:704 + InvokeBehaviourNetworkSpawn callers |

| 3 | Legacy [ServerRpc] method names must end with ServerRpc; [ClientRpc] must end with ClientRpc (ILPP enforced at compile time). | Editor/CodeGen/ ILPP validators |

| 4 | New [Rpc(SendTo.X)] has no naming constraint; SendTo has 11 values. | Runtime/Messaging/RpcTargets/RpcTarget.cs:9-80 |

| 5 | PlayerPrefab must exist in NetworkPrefabsList or NetworkConfig.Prefabs or 2.x runtime rejects it. | Runtime/Configuration/NetworkConfig.cs:40 + NetworkPrefabsList.cs:14 |

| 6 | Nested NetworkObjects are forbidden (NetworkObject inside another NetworkObject prefab). Re-parent at runtime via TrySetParent. | Runtime/Core/NetworkObject.cs:2135-2215 |

| 7 | NetworkVariable<T> requires T to be unmanaged or implement INetworkSerializable. string, List<>, class are rejected. | Runtime/NetworkVariable/NetworkVariable.cs:12 + ILPP |

| 8 | NetworkList<T> requires T: unmanaged, IEquatable<T>. It is NOT NetworkVariable<List<T>>. | Runtime/NetworkVariable/Collections/NetworkList.cs:14 |

| 9 | NetworkSceneManager.LoadScene/UnloadScene is Server-only. | Runtime/SceneManagement/NetworkSceneManager.cs:1496, 1252 |

| 10 | UnityTransport.SetRelayServerData and SetConnectionData are mutually exclusive; use one or the other. | Runtime/Transports/UTP/UnityTransport.cs:776-897 |

Sub-doc Routing

| Sub-doc | When to read |

|---------|--------------|

| LIFECYCLE.md | Lifecycle, callback ordering, Awake/OnNetworkSpawn/Start differences |

| OWNERSHIP.md | IsOwner/IsServer/IsHost permission matrix, ChangeOwnership, Distributed Authority |

| RPC.md | Choosing RPC attributes, SendTo semantics, RpcInvokePermission, deprecated paths |

| VARIABLES.md | NetworkVariable/NetworkList init and serialization constraints |

| SPAWNING.md | Prefab registration → Spawn → Despawn, GlobalObjectIdHash, SpawnAsPlayerObject |

| SCENE.md | NetworkSceneManager, EnableSceneManagement, in-scene object sync |

| TRANSPORT.md | UnityTransport direct / Relay / DebugSimulator configuration |

| PITFALLS.md | 30 concrete hallucination pitfalls |

Routing to Other Modules

• Generating NetworkBehaviour scripts → use the functional netcode module's netcode_add_network_behaviour_script
• Bulk attaching NetworkObject/NetworkTransform in the scene → netcode module Components skills
• Architecture-level decisions (Server-authoritative vs Distributed Authority) → also load architecture

Version Scope

This document targets com.unity.netcode.gameobjects 2.x (validated against 2.11.0, Unity 6000.0+). Some APIs (SendTo.Authority, RpcInvokePermission, the universal [Rpc] attribute) do not exist in 1.x.