The Client-Server Model in Roblox
In Roblox, the server is an authoritative game instance that runs Scripts under ServerScriptService and ServerStorage. Clients are the player instances that run LocalScripts under StarterPlayerScripts, StarterCharacterScripts, and PlayerGui. The server and client communicate through RemoteEvents (fire-and-forget messages) and RemoteFunctions (request-response calls). The critical rule is that the server can see and modify everything, while the client can only see what the server replicates to it. Exploiters cannot access ServerStorage or ServerScriptService. They can, however, read and modify anything on the client, including all LocalScripts, ReplicatedStorage modules, and the local workspace hierarchy.
Why Clients Lie
Roblox exploiters use script injection tools that let them execute arbitrary Luau code on the client. This means they can fire any RemoteEvent with any arguments, modify their character properties locally, teleport their position, speed up animations, and read any client-accessible code. If your server receives a RemoteEvent like DealDamage(targetId, 9999) and applies it without validation, exploiters will one-shot every player and NPC in your game. If your shop system fires BuyItem(itemId) and the server does not verify the player has enough currency, exploiters get everything for free. Every piece of data from the client must be treated as untrusted input.
Validation Patterns for RemoteEvents
Every server-side RemoteEvent handler should follow the same validation structure: verify the player argument exists and is valid, type-check all additional arguments, range-check numerical values, verify spatial conditions like distance, and confirm the player is in a valid state to perform the action. For a combat system, when the client fires an attack event, the server should check: is the player alive? Is the target alive and within range? Has the attack cooldown elapsed on the server clock? Is the weapon equipped? Only after all checks pass should the server apply damage. Store cooldown timestamps, player states, and inventory on the server. Never read these values from the client.
- Type-check every argument: if typeof(targetId) ~= "number" then return end
- Range-check values: if damage < 0 or damage > MAX_DAMAGE then return end
- Distance validation: if (attacker.Position - target.Position).Magnitude > MAX_RANGE then return end
- State validation: if not playerState[player].isAlive then return end
- Cooldown enforcement: if tick() - lastAttack[player] < COOLDOWN then return end
Damage Validation and Hit Registration
The most exploited system in Roblox games is combat. The safest approach is fully server-side hit detection, where the server performs raycasts or overlap checks to determine hits. However, this adds latency. A common compromise is client-predicted hit registration with server validation. The client sends a hit request with the target and the server verifies the distance, line of sight, weapon state, and cooldown. If any check fails, the hit is rejected. For competitive games, you can add additional checks like velocity validation (was the player moving at a reasonable speed) and hit-rate limiting (no more than N hits per second). Accept that some edge-case hits will be rejected. This is vastly preferable to allowing exploits.
Movement and Speed Validation
Speed hackers modify their character Humanoid.WalkSpeed or apply direct velocity changes on the client. The server should periodically check player positions against expected movement speeds. Record the player position every few seconds and calculate whether the distance traveled is physically possible given their WalkSpeed and JumpPower. Do not kick players instantly for a single violation since network lag can cause legitimate teleports during rubber-banding. Instead, use a violation counter that resets over time. Three violations in ten seconds is a reasonable threshold for a teleport-back or soft punishment. Hard bans should only come from sustained, obvious cheating.
Building a Security-First Mindset
Server-authoritative design is not something you add after building your game. It is a mindset that informs every architectural decision from the start. When you add a new feature, ask: what happens if the client lies about this? If the answer involves losing game integrity, you need server validation. Keep your server-side code clean and modular so validation logic is easy to add and maintain. Use ModuleScripts to centralize validation functions that multiple handlers can share. The cost of building secure systems upfront is a fraction of the cost of patching exploits after launch while your playerbase watches.