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Server-authoritative pub/sub event messaging for multiplayer - publish from anywhere, listen from anywhere, no direct references required. One component, zero GAS dependency.

Built for Unreal Engine 5 with server-authoritative replication, transparent client-to-server routing, four delivery scopes, a late-join persistent event cache, a two-tier delegate system, and a full Blueprint API. Includes a C++ demo character, Blueprint helper library, and complete documentation.

The Problem

Multiplayer games need decoupled communication between systems - a player dies, a zone is captured, a match phase changes. Wiring direct actor references across systems creates brittle dependencies. Blueprint Game Events don't replicate. Building a proper replicated pub/sub system from scratch means handling RPCs, authority checks, late-join state, and keeping it all Blueprint accessible.

The Solution

AP Event Bus - a single component on your GameState. Any actor publishes a named event by Gameplay Tag. Any actor listens by Gameplay Tag. Publishers and listeners never reference each other. Client-to-server routing is automatic - one PublishEvent node works from any machine without authority checks.

Everything replicates automatically. Server-authoritative delivery. RPC-based replication. Late-join clients receive all persistent event state on connect.

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Part of the AfterPrime GAS-Free Multiplayer Stack

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AP Event Bus is the communication backbone of the AfterPrime plugin suite — production-grade multiplayer gameplay systems that work together, all without GAS. Every plugin follows the same architecture: server-authoritative, Gameplay Tag-keyed, single component, Blueprint-first, FastArray replicated. Try this free plugin to see the AfterPrime quality standard, then explore the full suite below.

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Core Features

▸ PUBLISH / SUBSCRIBE ARCHITECTURE

Any actor publishes events onto the bus by Gameplay Tag. Any actor listens for events by tag. No direct actor references required between publishers and subscribers - fully decoupled event-driven design. No manager actors, no subsystems, no GAS dependency.

▸ TRANSPARENT CLIENT-TO-SERVER ROUTING

Call PublishEvent from a client, the server, or anywhere - one node handles all routing automatically via Server RPC. No authority checks, no separate functions for different network roles. One node works from anywhere.

▸ FOUR DELIVERY SCOPES

• All - server fires + NetMulticast to all connected clients

• OwnerOnly - server fires + Client RPC to the owning connection only

• ServerOnly - server fires locally, zero client cost

• LocalOnly - fires on calling machine only, zero network cost - ideal for UI-only events

▸ LATE-JOIN CACHE - PERSISTENT EVENTS

Register tags as persistent so their last payload is cached server-side. Late-joining clients automatically receive all cached events on connect - no manual state sync required. Match phase changes, captured objectives, and world state transitions arrive correctly for players who join mid-game.

▸ TWO-TIER DELEGATE SYSTEM

OnEventReceived fires for every event on the bus regardless of tag - catch-all listening. OnListenedEventReceived fires only for tags registered via ListenForEvent - filtered listening. Use both simultaneously on the same component.

▸ CACHE QUERY API

WasEventFired, GetLastPayload, GetAllCachedEventTags. Query persistent event state directly without waiting for a delegate.

▸ BLUEPRINT HELPER LIBRARY

GetEventBusFromGameState, GetEventBusComponent, PublishEventOnBus, MakeEventPayload. Convenience functions available in any Blueprint graph - no component reference hunting required.

▸ BUILT FOR MULTIPLAYER

Server-authoritative architecture. RPC-based replication - no replicated UPROPERTYs. Full late-join state reconstruction for persistent events. Tested with dedicated servers and listen servers.

▸ 100% BLUEPRINT ACCESSIBLE

Every method, every delegate, every query exposed to Blueprint. Organized under AP|EventBus categories. C++ users get full access to the same API.

What's Included

• C++ plugin - Runtime module, full source included

• Blueprint helper library with 4 convenience functions

• C++ demo character with input-driven publish examples across all four delivery scopes

• Quick Start Guide, full API Reference, and Changelog

Who Is This For?

• Multiplayer developers who need decoupled communication between gameplay systems without building a replicated event bus from scratch

• Teams who want Blueprint-accessible event-driven architecture without GAS or complex dependencies

• Projects where late-join state synchronisation for game events is required - match phases, objectives, world state changes

• Any project that wants cleaner system boundaries and less direct actor coupling between gameplay systems


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The AfterPrime GAS-Free Multiplayer Stack

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Build complete multiplayer gameplay systems - no GAS required. Every AfterPrime plugin shares the same architecture: server-authoritative, Gameplay Tag-keyed, single component, Blueprint-first, FastArray replicated.

▸ AP Timer Suite - Replicated Timers + Threshold Events - Server-authoritative timer management with threshold callbacks, late-join correctness, and an optional inspector overlay. Timers for cooldowns, match phases, objectives, and more.
▸ AP Replicated Cooldowns System - Ability cooldown management with charge systems, global cooldowns, cooldown reduction, shared cooldown groups, and a UI-ready query API.
▸ AP Replicated Status Effects System - Buffs, debuffs, DoTs, HoTs, and status conditions with five stacking policies, tag-based immunity, effect interaction rules, and a buff bar UI widget. The most advanced plugin in the suite.

▸ AP Replicated Attributes System - Health, Stamina, Mana, Shield, or any float-based attribute with modifiers, regeneration, and full replication.

All plugins are standalone - use one or combine them for a complete GAS-free multiplayer combat stack.