WebSocket is a critical building block for multiplayer apps. But once you start building, you quickly run into the harder problems: flaky connections, reconnection, presence, shared state, room lifecycle, and keeping multiple actors in sync.
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Most teams start building a multiplayer app by saying, “we just need WebSockets”. That’s true for about a week. Then the real problems show up. Connections drop. Tabs go offline. Users reconnect from another device. Two people edit the same thing at once. Presence gets out of sync. A comment appears in one place but not another. A room goes idle, wakes up again, and now the UI isn’t sure what state it should trust.
WebSocket matters a lot. It’s the backbone of most realtime products. But in a multiplayer app, opening a WebSocket connection is only one layer of the job. The hard part of realtime collaboration starts right after that.
It’s tempting to say WebSocket is the easy part, and everything else is hard. That’s not really true. WebSocket already introduces a whole new class of problems compared to a normal request-response app. The moment you keep a long-lived connection open, you now have to think about flaky networks, heartbeats, missed updates, reconnect logic, connection status, retry storms, and what should happen when a client disappears mid-session.
That complexity becomes much more obvious in collaborative products. Imagine someone editing a document on a train. Their connection drops for a few seconds. They keep typing. Then the tab reconnects. What should happen next? Which updates need to be replayed? Which state is still valid? Should other collaborators still see that person as present? If so, for how long? Those are WebSocket problems, and users feel them immediately when they’re handled badly.
Even with a solid WebSocket layer, multiplayer apps get much harder the moment multiple actors are working on the same data at the same time. That is the part people tend to underestimate. A multiplayer app is not just a stream of events flying around over a socket. It’s a stateful system where users, back end workflows, and now AI agents can all read and write shared data concurrently.
That means transport is not enough. You also need a way to keep shared state correct, visible, and responsive under constant change. This is where the sync engine starts to matter. A sync engine decides how updates are applied, merged, streamed, persisted, and replayed. It’s the layer that turns raw transport into something people can actually collaborate on. Without it, every new feature starts pulling the system apart.
This is usually the first real wall teams hit. Two people update the same piece of data at the same time. Or one person and one AI agent do. Or a backend workflow modifies the same record while someone is still editing it in the UI. Now what?
If you only think in terms of message delivery, you end up asking the wrong question: did the event arrive? The real question is: what should the shared state become? That’s a sync problem, not just a transport problem.
Presence sounds simple until you build it. Live cursors. Avatar stacks. Typing state. Selections. Active tools. Who is viewing what. Who is editing what. Which agent is currently doing work.
These signals are ephemeral, but they’re a huge part of what makes realtime collaboration feel alive. They’re also tightly connected to the shared state itself. A cursor without the right document state is confusing. A selection without the right text range is broken. A typing indicator without reliable connection state becomes noise.
This is why presence is not just UI polish. It is part of the collaborative model. The best multiplayer products don’t treat it as an afterthought. Presence and shared state need to evolve together.
This is one of the least glamorous parts of multiplayer, and one of the most important. Users refresh. Laptops sleep. Browsers freeze background tabs. Mobile connections bounce between Wi-Fi and cellular. A server restarts. A room goes idle and wakes up again. A client reconnects after missing a burst of updates.
All of those moments need to feel seamless. If they don’t, users stop trusting the product. They start wondering whether the document is stale, whether their comment was sent, whether someone else saw their changes, whether the system is still live. You can’t fake your way through this part. A good multiplayer product needs a connection engine that can recover gracefully, restore state, and make connection status legible to the UI.
Multiplayer apps don’t live in perfect network conditions.
Another thing teams discover late: multiplayer apps need structure. A socket server can move events around, but collaborative products need a shared context around the work. A document. A whiteboard. A design file. A ticket. A conversation. A project plan.
That’s why rooms matter. A room gives you a clean collaboration surface where people, agents, and backend systems can operate on the same artifact in realtime. It also gives you isolation. Presence belongs to that room. Shared state belongs to that room. Comments and threads belong to that room. Notifications may surface elsewhere, often at the user or workspace level, but they still derive from activity in that room. Without that kind of model, teams usually end up stitching together a growing pile of systems that were never meant to behave like one product.
Rooms give multiplayer systems structure and isolation.
This is where things get surprisingly tricky. Undo and redo in a multiplayer app can’t work like they do in a single-player app. If one user presses undo, they shouldn’t erase everyone else’s work. Selections need to stay meaningful as content shifts underneath them. Mentions need to notify the right person without spamming everyone. Comments need to appear live in context, not as a separate disconnected stream.
For instance, one of the most commonly used approaches to handle undo/redo is to save the application’s previous states and rewind through those when the user hits undo.
An interactive visualization displaying a canvas and its multiple states across time.
Single-player undo/redo
In a multiplayer app, nailing the UX of undo/redo is much more complex. It’s important to account for more than just the state of the document. Selection state and group intermediary commands need to be accounted for as well.
An interactive visualization displaying two side-by-side canvases and users keeping their selections after others hit undo or redo.
Multiplayer undo/redo accounting for selection state
If you’re interested in how we handle multiplayer undo/redo at Liveblocks, you can read our article on how to build undo/redo in a multiplayer environment.
Multiplayer apps are no longer just a few browser tabs talking to each other. Now you may also have background workflows, automations, and AI agents participating in the same experience. They may read shared state, leave comments, update records, post messages, or show live presence while they work.
That changes the architecture. Suddenly, your collaboration layer has to support more than a client-side WebSocket connection. It also needs to support server-side participation. It needs a model where people and agents can work in the same room, on the same state, with the same visibility.
That’s part of why multiplayer is becoming more important in the AI era, not less. Agents increase the number of actors in the system. That makes concurrency, coordination, and visibility more important too. I wrote more about that shift in AI agents are becoming native users of software, and you can see it more concretely in customer stories like how Magic Patterns powers its collaborative AI design experience.
By the time a multiplayer app is production-ready, most teams have built far more than a socket layer.
They’ve built a connection engine for flaky networks and reconnection. A sync engine for shared state. A presence system. A room model. Durable storage. Replay and catch-up logic. Comments and threads. Notification logic. Back end workflows. Observability around room health and connection quality.
That’s the part nobody tells you at the beginning. Multiplayer apps are not just realtime apps. They are coordination systems.
WebSocket is still the right foundation for many multiplayer products. It gives you low-latency, bidirectional communication and the responsiveness people expect from collaborative software. WebSockets are foundational to realtime collaboration, but they are not the whole architecture.
But WebSocket is not the product architecture. It’s the transport layer underneath a much bigger system: one that has to keep shared state correct, make presence feel alive, recover from bad networks, and coordinate multiple humans and agents in the same flow.
That’s why the best collaborative products feel simple on the surface and complex underneath. They hide the hard parts well.
If you’re building a multiplayer product, WebSocket is absolutely part of the job. It’s also not enough. The part nobody tells you is that once your app becomes collaborative, the real challenge is no longer just opening a connection. It’s keeping state correct, visible, and responsive as multiple actors work at once, often over unreliable networks, inside a system that has to recover gracefully when reality gets messy.
Problem | Symptom | What solves it |
|---|---|---|
| Concurrent edits | Changes arrive, but the shared state is still wrong | A sync engine with conflict resolution |
| Presence | Cursors, selections, and typing state drift out of context | A presence system tied to the same realtime collaboration model |
| Reconnection and offline states | Users stop trusting whether the document is current | A connection engine with replay, catch-up, and recovery |
| Room lifecycle and isolation | Features feel stitched together instead of product-shaped | A room model with clear boundaries and ownership |
| Multiplayer UX details | Undo, mentions, and comments break under concurrency | Product behaviors built on top of the sync model, not just UI |
| Backend systems and AI agents | Humans and automations update the same state without visibility | Server-side participation in the same collaboration layer |
That’s what makes multiplayer hard. And that’s also what makes it worth getting right. If you’re exploring how to build this kind of product, our get started guides are a good place to begin.