Post
Your game guesses what the server will say so you do not have to wait for permission to move.
Client-side prediction is the technique where your local game client immediately acts on your inputs -- moving your character, firing your weapon -- without waiting for the server to confirm. The client predicts what the server's response will be based on the game's rules, and when the server's actual response arrives, it reconciles any differences. If the prediction was wrong, the client silently corrects with a rollback. Done well, it makes a 100ms connection feel instant. Done poorly, you get rubber-banding where your character snaps back to a previous position because the server disagreed with your client.
Example
Rocket League uses aggressive client-side prediction combined with server reconciliation to make car movement feel perfectly responsive even at higher pings, which is critical when you need frame-perfect aerial hits in a physics-based game.
Why it matters
Without client-side prediction, every online game would feel like you are playing through remote desktop -- a noticeable delay on every input. It is the core illusion that makes online multiplayer feel responsive and playable across real-world internet connections.
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