Post
Never trust the client -- the server is the only source of truth about what actually happened.
Server authoritative design is the networking architecture where the server has final say over all game state. The client sends inputs (I pressed shoot, I moved left), and the server validates those inputs, simulates the result, and sends back the authoritative state. The client never directly modifies game state -- it only renders what the server tells it. This prevents the most common category of cheats: a client that claims 'I have infinite health' or 'I teleported to this position' gets overruled because the server knows neither of those things happened. The tradeoff is latency -- every action must round-trip to the server before being confirmed, which is why client-side prediction is used to mask the delay. The server also needs enough compute power to simulate everything, which gets expensive at scale.
Example
Fortnite runs a server authoritative model where the server validates every shot, every building placement, and every player position. When players experience 'ghost shots' (shooting through an opponent with no damage), it is usually because the server's authoritative position of the target differed from what the client was showing -- the price of security over responsiveness.
Why it matters
Server authoritative design is the only reliable foundation for fair multiplayer gaming. Any system that trusts client-reported data will be exploited. The entire modern competitive gaming ecosystem depends on servers that validate reality rather than accepting whatever clients claim happened.
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