Adapt: Single to Multiplayer

Expert guidance for retrofitting multiplayer into single-player games.

NEVER Do (Expert Multiplayer Rules)

Security & Authority

• NEVER trust client-reported state — Clients own their 'Input', NOT their 'Position' or 'Health'. Server must validate every coordinate and health change.
• NEVER use get_tree() groups for authority checks — Use is_multiplayer_authority(). Group registration is non-deterministic in high-latency joins.
• NEVER allow unrestricted RPC rates — A malicious client can call a 'FireWeapon' RPC 10,000 times per second. Always implement rate-limiting (net_rpc_rate_limiter.gd).

Movement & Lag

• NEVER skip Client-Side Prediction — Movement without prediction feels 'heavy' and unresponsive. Predict movement locally, then correct only on server disagreement.
• NEVER sync peers at 60Hz — Sending entire state every frame will saturate client bandwidth. Use a lower tick-rate (20-30Hz) and interpolate between packets.
• NEVER snap peer positions — Abrupt position updates cause 'jitter'. Store a buffer of past states and lerp between them with a 100ms delay.