Table of Contents

Getting Started

This guide walks you through setting up SteamNetworkLib in a Schedule 1 MelonLoader mod and implementing the minimal loop.

Installation

Prerequisites

  1. MelonLoader installed on Schedule 1
  2. Steam client running
  3. Schedule 1 launched through Steam
  4. Basic C# and MelonLoader modding knowledge
  5. Visual Studio or VS Code

Add SteamNetworkLib to Your Mod Project

Target .NET Standard 2.1 (works for Mono and Il2Cpp) and reference SteamNetworkLib:

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <TargetFramework>netstandard2.1</TargetFramework>
    <AssemblyTitle>YourScheduleOneMod</AssemblyTitle>
    <AssemblyVersion>1.0.0</AssemblyVersion>
  </PropertyGroup>
</Project>

Add references to:

  • MelonLoader.dll
  • UnityEngine.dll
  • Assembly-CSharp.dll
  • SteamNetworkLib.dll

Download the matching SteamNetworkLib DLL from the GitHub releases page, keep that DLL in your mod project or local dependency folder, and reference the runtime-specific binary:

  • Mono mods/configurations must reference the Mono release DLL
  • Il2Cpp mods/configurations must reference the Il2Cpp release DLL

Do not mix these references across build targets, and do not point your mod project at a sibling ..\SteamNetworkLib\bin\... source checkout.

If your mod has separate Mono and Il2Cpp configurations, reference the downloaded DLLs conditionally in your .csproj:

<ItemGroup Condition="'$(Configuration)'=='Mono' or '$(Configuration)'=='MonoDebug'">
  <Reference Include="SteamNetworkLib">
    <HintPath>libs\SteamNetworkLib\Mono\SteamNetworkLib.dll</HintPath>
  </Reference>
</ItemGroup>

<ItemGroup Condition="'$(Configuration)'=='Il2cpp' or '$(Configuration)'=='Il2cppDebug'">
  <Reference Include="SteamNetworkLib">
    <HintPath>libs\SteamNetworkLib\Il2cpp\SteamNetworkLib.dll</HintPath>
  </Reference>
</ItemGroup>

When to initialize

SteamNetworkLib requires the game process to have Steamworks attached and initialized. In Schedule One mods, that is not always true during OnInitializeMelon(), and it is common for users to launch in a way where Steamworks is unavailable. Treat networking as an optional capability until initialization succeeds.

Recommended lifecycle:

  • Create the SteamNetworkClient in OnInitializeMelon() or when your network feature starts.
  • Attempt initialization after the menu or first relevant scene has loaded, then retry on a short timer if Steamworks is not ready.
  • Keep your mod's single-player/local behavior working when initialization fails.
  • Call ProcessIncomingMessages() every frame only after the client is initialized.
  • Dispose the client in OnDeinitializeMelon().

Use TryInitialize() for normal consumer mods. Use Initialize() only when networking is mandatory and a thrown exception should fail the feature immediately.

Minimal mod setup

using MelonLoader;
using SteamNetworkLib;
using SteamNetworkLib.Core;
using SteamNetworkLib.Exceptions;
using UnityEngine;

public class YourScheduleOneModMain : MelonMod
{
    private SteamNetworkClient client;
    private float nextNetworkInitAttempt;
    private bool multiplayerAvailable;

    public override void OnInitializeMelon()
    {
        // Optional: configure network rules (relay, session policy, channels)
        var rules = new NetworkRules
        {
            EnableRelay = true,
            AcceptOnlyFriends = false
        };

        client = new SteamNetworkClient(rules);
    }

    public override void OnSceneWasInitialized(int buildIndex, string sceneName)
    {
        if (sceneName == "Menu")
        {
            TryInitializeNetworking();
        }
    }

    public override void OnUpdate()
    {
        if (!multiplayerAvailable && Time.realtimeSinceStartup >= nextNetworkInitAttempt)
        {
            TryInitializeNetworking();
        }

        if (multiplayerAvailable)
        {
            client.ProcessIncomingMessages();
        }
    }

    public override void OnDeinitializeMelon()
    {
        client?.Dispose();
    }

    private void TryInitializeNetworking()
    {
        if (client.IsInitialized)
        {
            multiplayerAvailable = true;
            return;
        }

        if (client.TryInitialize(out var error))
        {
            multiplayerAvailable = true;
            client.OnLobbyCreated += (s, e) => MelonLogger.Msg($"Lobby: {e.Lobby.LobbyId64}");
            MelonLogger.Msg("SteamNetworkLib initialized.");
            return;
        }

        multiplayerAvailable = false;
        nextNetworkInitAttempt = Time.realtimeSinceStartup + 2f;
        MelonLogger.Warning($"Steam networking unavailable, retrying later: {error?.Message}");
    }
}

If multiplayer is optional, guard every sync/send path with your own multiplayerAvailable flag and keep local logic active. Do not call lobby, member data, SyncVar, or P2P methods before initialization succeeds.

Working with Steam IDs

SteamNetworkLib still exposes the native CSteamID for Steamworks interop, but common identity lookups also have runtime-neutral helpers:

if (client.TryGetHostMember(out var host))
{
    MelonLogger.Msg($"Host: {host.DisplayName} ({host.SteamId64})");
}

ulong localPlayer = client.LocalPlayerId64;
ulong hostPlayer = client.HostPlayerId64;

foreach (var member in client.GetRemoteMembers())
{
    MelonLogger.Msg($"Remote member: {member.DisplayName} ({member.SteamIdString})");
}

Prefer the ulong properties for config files, JSON payloads, dictionaries, and logs. Convert back to CSteamID only when you call an API that requires the Steamworks type.

Best Practices

  • Use unique prefixes for your mod's data keys to avoid collisions with other mods. See Data Synchronization for details.
  • Fail open for optional multiplayer. If Steamworks is unavailable, log once or retry quietly and keep single-player behavior working.
  • Retry instead of crashing when Steamworks is not ready. TryInitialize() is intended for this path.

From here, pick the guide you need next:

  • Lobby Management: create/join/leave/invite
  • Data Synchronization: lobby and member data
  • P2P Messaging: typed messages, files, channels
  • Events and Errors: event model and exceptions
  • Recipes: copy-paste snippets for common tasks
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