How do I know if my game has a desync problem?

Look for clients in the same session ending up with different game states. The defining sign is players seeing different things, positions, scores, or world state not matching between clients (reports of 'it looked different on my screen'), which means the clients have diverged, the essence of desync. A sign is confusing bugs that only happen with multiple players (not single-player) and depend on the interaction between clients, outcomes that don't make sense or register differently for different players, inconsistent and hard to reproduce. And player-reported signs include complaints that something happened differently for different players (a hit registering for one but not another, different outcomes on each screen). To diagnose, capture crashes and errors from both clients and the server, since desync depends on the interaction between machines, seeing issues from both sides (and how they disagree) is how you trace where the state diverges. If players report seeing different states, you have confusing multiplayer-only bugs, or players complain about things differing between them, you have a desync problem, clients diverging from one another, which is a multiplayer-specific failure rooted in distributed state and unreliable networks. The inconsistency and difficulty reproducing it are hallmarks of desync (it depends on timing and network conditions), which is why field capture from both clients and server is valuable, it lets you see the divergence that's hard to reproduce locally.

What causes desync in multiplayer games?

Clients ending up with different game states, which happens when they diverge without a single authoritative source of truth, compounded by the network's unreliability. If clients each compute important state independently, small differences, in timing, in the order events are processed, in floating-point results, accumulate until they have meaningfully different states (desync). The unreliable network makes it worse: messages arriving late, out of order, or lost mean clients receive updates at different times or miss them, causing them to drift apart even if they'd otherwise stay aligned. Without a mechanism to reconcile clients back to a correct state, these divergences persist and grow, producing the confusing bugs where players see different things. So desync is caused by distributed state diverging, clients computing state independently (so they drift) under an unreliable network (which delivers updates imperfectly), without a single source of truth to keep them aligned. This is why desync is inconsistent and hard to reproduce: it depends on the timing, network conditions, and combinations of client states, which vary from session to session, so it manifests unpredictably and is hard to recreate locally (which is why capturing issues from clients and the server in the field, to see the divergence under real conditions, is valuable). The prevention addresses the root: make the host or an authoritative server the source of truth for important state, so clients reconcile to it rather than diverging independently (the most reliable desync prevention, since there's one correct state everyone converges on), handle the network's unreliability robustly (so late and missing messages don't cause lasting drift, with clients reconciling back to the authoritative state), and validate state (so bad peer data doesn't diverge others). So desync is caused by clients diverging, from independent state computation and unreliable network delivery, without a single source of truth, and preventing it requires an authoritative source of truth plus robust network handling and reconciliation, which is a deliberate architectural choice, not something that happens automatically.

How do I fix desync in my multiplayer game?

Establish a single source of truth (an authoritative server or host), handle the network's unreliability with reconciliation, and validate state, so clients converge on one correct state rather than diverging. The root cause of desync is clients diverging without a single source of truth under an unreliable network, so the fixes target that: make the host or an authoritative server the source of truth for important state, so clients reconcile to it rather than computing state independently and drifting, this is the most reliable fix, since it gives the game one correct state that all clients converge on, preventing the divergence that is desync. Handle the network's unreliability robustly: account for late and missing updates, and reconcile clients back to the authoritative state when they drift (so a temporary divergence from a missed or late message is corrected rather than persisting), don't assume updates arrive cleanly. Validate incoming state and inputs rather than trusting peers, so a buggy, desynced, or malicious client can't push state that diverges others. To diagnose and verify, capture crashes and errors from both clients and the server (to see when and where desync occurs, since it's hard to reproduce locally, and to confirm fixes reduce it). So you fix desync by giving the game a single source of truth (authoritative server/host that clients reconcile to), handling the network defensively with reconciliation (so imperfect delivery doesn't cause lasting drift), and validating state (so bad peer data doesn't diverge others), with field capture from clients and server to see the desync and verify the fix. An authoritative server/host model is generally the most robust approach, since it provides the single source of truth that makes desync prevention tractable (clients converge on the authority's state) and also helps with related multiplayer problems (it can validate and control the shared state, preventing one client crashing or diverging others). Desync is one of the hardest multiplayer problems because it arises from distributed state under unreliable networks (inherently hard to reason about and reproduce), so fixing it requires these deliberate architectural defenses, authoritative state, reconciliation, validation, rather than ad-hoc patches, and capturing the desync from the field (across clients and server) is what lets you see and verify the fix for a problem that's hard to reproduce in development.

Signs Your Game Has a Desync Problem

Quick answer: Watch for players seeing different game states, positions or outcomes not matching between clients, confusing multiplayer-only bugs, and complaints about things differing between players. Desync is clients diverging from one another.

Desync, clients in a multiplayer session ending up with different game states, produces confusing bugs and breaks the shared experience. Here are the signs your game has a desync problem.

Players Seeing Different Game States

The defining sign is players in the same session seeing different things, positions, scores, or world state not matching between clients. If one player sees an outcome and another sees something different, the clients have diverged, which is desync. Reports of 'it looked different on my screen' point directly at it.

Bugnet captures crashes and errors from clients and the server, so divergence-related issues surface. Players seeing different game states is the defining sign of desync, and because it depends on the interaction between machines, capturing issues from both clients and the server (to see the divergence) is important for diagnosing it.

Confusing Bugs That Only Happen With Multiple Players

A sign is confusing bugs that only occur in multiplayer (not single-player) and depend on the interaction between clients, outcomes that don't make sense, actions that register differently for different players. If you have bugs that only manifest with multiple players and seem inconsistent, desync is a likely cause.

Bugnet captures crashes and errors with context from clients and server, so multiplayer-only issues are identifiable. Confusing multiplayer-only bugs are a sign of desync, since they arise from the distributed state diverging between clients, which is why they're inconsistent and hard to reproduce, and why field capture from both sides helps trace them.

Complaints About Things Differing Between Players

Player-reported signs include complaints that something happened differently for different players, a hit that registered for one but not another, a different outcome on each screen, the game state disagreeing. These complaints point at clients diverging, the players are experiencing the desync directly.

Bugnet captures issues from the field across clients, so you can see the divergence players report. Complaints about things differing between players are players directly experiencing desync, and capturing the issues (from both clients) helps you see where the state diverges, pointing at the synchronization problem to fix (often a missing single source of truth or network-handling issue).

Watch for players seeing different game states, positions or outcomes not matching between clients, confusing multiplayer-only bugs, and complaints about things differing between players. Desync is clients diverging from one another.