Talk to your players' client.

Install

Use it from your plugin

Add the API jar as a compileOnly / provided dependency and depend: [EmberBridge] in your plugin.yml. The API is split into modules (EmberBridge.module(...)): Nametag, StaffMod, Notification, Waypoint, Cooldown, Title, Team, Vignette and ModSetting. Each takes Recipients: one player, a list, or everyone on Solar. Everything runs on the main thread.

import gg.ember.bridge.api.*;

public final class ArenaListener implements Listener {
    private final NametagModule nametags = EmberBridge.module(NametagModule.class);
    private final StaffModModule staff = EmberBridge.module(StaffModModule.class);
    private final CooldownModule cooldowns = EmberBridge.module(CooldownModule.class);

    @EventHandler
    public void onEmberJoin(EmberPlayerJoinEvent e) {
        Player p = e.getEmberPlayer().getPlayer();
        Recipients them = Recipients.of(p);

        EmberBridge.module(NotificationModule.class).displayNotification(them,
            Notification.builder().title("Welcome to the arena").body("First to 5 kills wins.").build());
        EmberBridge.module(ModSettingModule.class).disableMods(them, Arrays.asList(EmberMod.ZOOM, EmberMod.FULLBRIGHT));
        EmberBridge.module(WaypointModule.class).displayWaypoint(them,
            Waypoint.builder("mid").name("Middle").location(arena.getCenter()).color("#FBBF24").build());

        // everyone on Ember sees this player's rank over their head (also players who join later)
        nametags.overrideNametag(Recipients.everyone(), p, Nametag.builder()
            .line(ranks.prefix(p))
            .line("&f" + p.getName())
            .build());

        // staff tools for moderators (on top of the emberbridge.staff.* permissions)
        if (p.hasPermission("arena.mod")) staff.enableStaffMods(them, StaffMod.XRAY, StaffMod.NAMETAGS);
    }

    @EventHandler
    public void onPearl(ProjectileLaunchEvent e) {
        if (!(e.getEntity() instanceof EnderPearl)) return;
        Player p = (Player) e.getEntity().getShooter();
        cooldowns.displayCooldown(Recipients.of(p),
            Cooldown.builder("pearl").name("Ender pearl").duration(15_000).color("#C084FC").build());
    }
}

Staff mods

Give the permission to your staff (ops have emberbridge.staff.* by default). They find the mods under Staff in the Solar mods menu, and only while they're on your server. Remove the permission and the mod turns off in their client within a second.

Nametags without code

Turn on nametags in the config and pick the lines. Placeholders: {name}, {displayname}, {health}, {world} and {ping}, with & color codes. Try one by hand with /emberbridge nametag <player> &cADMIN | &fName.

Mods you can turn off

The protocol

Not on Bukkit? It's plain JSON on the ember:bridge plugin channel, so any server software can speak it. Solar registers the channel when it joins and then says hello.

// server → client, on the "ember:bridge" plugin channel (UTF-8 JSON)
{"type":"notification","title":"Welcome","body":"Have fun"}
{"type":"waypoint.add","id":"mid","name":"Middle","x":0,"y":64,"z":0,"color":"#FBBF24"}
{"type":"waypoint.remove","id":"mid"}      {"type":"waypoint.clear"}
{"type":"cooldown.add","id":"pearl","name":"Ender pearl","millis":15000,"color":"#C084FC"}
{"type":"cooldown.remove","id":"pearl"}
{"type":"rules","disabled":["zoom","fullbright"]}
{"type":"vignette","color":"#E11D2E","opacity":0.4}
{"type":"title","title":"Round 1","subtitle":"Fight!","fadeIn":300,"stay":2000,"fadeOut":600}
{"type":"team","color":"#4ADE80","members":[{"uuid":"…","name":"Kairo","x":12.5,"y":64,"z":-3.2}]}
{"type":"nametag","uuid":"…","lines":["§c§lADMIN","§fKairo","§a20 HP"]}   // protocol 3
{"type":"nametag.reset","uuid":"…"}      {"type":"nametag.clear"}
{"type":"staff","mods":["xray","nametags"]}   // the whole list: anything missing turns off

// client → server, right after joining
{"type":"hello","protocol":3,"version":"0.55.0+1.8.9","mc":"1.8.9"}

Limits: 64 waypoints, 8 cooldowns and 32 teammates per player, cooldowns up to 1 hour, notification titles up to 60 characters, big titles up to 40, nametags up to 4 lines of 64 characters. Nametags and staff mods need protocol 3 (Solar 0.55 and newer); the plugin doesn't send them to older clients. The team list is sent whole every time (members missing from it are removed). Everything is cleared when the player leaves your server.