csharpfritz/aspire-minecraft/rcon-minecraft-commands

SKILL: RCON Minecraft Commands

Patterns for sending Minecraft RCON commands from the Worker service to create in-game effects.

When to Use

When implementing new in-world features that send RCON commands to the Minecraft server — particles, sounds, titles, boss bars, weather, entity spawning, scoreboard updates, etc.

Command Format Reference

Particle Effects

particle minecraft:{type} {x} {y} {z} {dx} {dy} {dz} {speed} {count} force

• force makes particles visible from far away (important for demo visibility)
• dx dy dz control the spread area (1 1 1 for a 2-block cube)
• Coordinates should align with StructureBuilder layout: BaseX=10, BaseY=-60, BaseZ=0, Spacing=6
• Particle center is at structure center: (BaseX + index*Spacing + 1, BaseY + 2, BaseZ + 1)

Title Screen Text

title @a times {fadeIn} {stay} {fadeOut}     // in ticks (20 ticks = 1 second)
title @a title {json}                        // main title (large text)
title @a subtitle {json}                     // subtitle (smaller text below)
title @a actionbar {json}                    // action bar (above hotbar)
title @a clear                               // clear current title

• JSON text format: {"text":"message","color":"red","bold":true}
• Set times BEFORE title/subtitle — order matters
• Colors: red, green, gold, gray, white, etc.

Weather

weather clear
weather rain
weather thunder

• No duration = persists until changed
• Only one weather state at a time — track last state to avoid redundant commands

Boss Bar

bossbar add {namespace:id} {json}            // create with display name
bossbar set {id} max {int}                   // max value (typically 100)
bossbar set {id} value {int}                 // current value (0 to max)
bossbar set {id} players @a                  // show to all players
bossbar set {id} visible true                // toggle visibility
bossbar set {id} color green|yellow|red|blue|pink|purple|white
bossbar set {id} name {json}                 // update display name
bossbar remove {id}                          // remove

• ID must be namespace:name format (e.g., aspire:fleet_health)
• ID must be lowercase
• Create once, then update value/color/name as needed

Sound Effects

playsound minecraft:{sound} {source} {selector} {x} {y} {z} {volume} {pitch}
playsound minecraft:{sound} {source} {selector}   // short form, plays at player location

• ~ ~ ~ for relative coordinates (plays at each player's location)
• Source channel: master, music, record, weather, block, hostile, neutral, player, ambient, voice
• Volume: float, 1.0 = normal
• Pitch: 0.5–2.0 (0.5 = half speed, 2.0 = double speed)

Architecture Pattern: Opt-in Features

Builder Extension Method (Hosting side)

public static IResourceBuilder<MinecraftServerResource> WithFeatureName(
    this IResourceBuilder<MinecraftServerResource> builder)
{
    var workerBuilder = builder.Resource.WorkerBuilder
        ?? throw new InvalidOperationException(
            "WithFeatureName() requires WithAspireWorldDisplay() to be called first.");
 
    workerBuilder.WithEnvironment("ASPIRE_FEATURE_FEATURENAME", "true");
    return builder;
}

Conditional Registration (Worker Program.cs)

if (!string.IsNullOrEmpty(builder.Configuration["ASPIRE_FEATURE_FEATURENAME"]))
    builder.Services.AddSingleton<FeatureNameService>();

Optional Injection (Worker BackgroundService)

file sealed class MinecraftWorldWorker(
    // ... required services ...
    FeatureNameService? featureName = null) : BackgroundService

Service Pattern

public sealed class FeatureNameService(
    RconService rcon,
    AspireResourceMonitor monitor,      // if aggregate feature
    ILogger<FeatureNameService> logger)
{
    private SomeState _lastState;       // track for transition-only logic
 
    public async Task DoSomethingAsync(IReadOnlyList<ResourceStatusChange> changes, CancellationToken ct)
    {
        // Only act when state changed (transition-only)
        if (newState == _lastState) return;
 
        await rcon.SendCommandAsync("command here", ct);
        _lastState = newState;
    }
}

Key Rules

1. Minimize RCON commands — track state, only send on transitions
2. Use `force` for particles — demos need visibility from spawn
3. Set title `times` before content — Minecraft processes them in order
4. Boss bar IDs are `namespace:name` — lowercase, colon-separated
5. Per-resource features (particles, titles, sounds) iterate changes list
6. Aggregate features (weather, boss bar) read monitor.HealthyCount/TotalCount
7. All services are opt-in — never break backward compatibility
8. Structure visual depth — layer fills in order: base shell (fill hollow), then overlay contrasting blocks (buttresses, weathering), then decorative elements (stairs, glass, iron bars). Later fills overwrite earlier ones, creating material variety without replace commands.
9. Block palette for depth — use 3+ block types per structure face: a primary (stone_bricks), a dark accent (deepslate_bricks), weathering (cracked/mossy), and decorative (chiseled, stairs, walls). Contrast creates perceived depth even on flat surfaces.
10. RCON budget accounting — count commands in the method AND all village overhead (fence, paths, health indicator, sign, BlueMap). The test asserts total < 100.