roblox-remote-events

name	roblox-remote-events
description	Use when implementing client-server communication in Roblox, firing events between LocalScripts and Scripts, passing data across the network boundary, syncing game state, or defending against exploits that abuse RemoteEvents or RemoteFunctions.

Roblox Remote Events & Functions

RemoteEvent vs RemoteFunction

Type	Direction	Returns value?	Use when
RemoteEvent	Any direction	No (fire-and-forget)	Notifying server of player action, broadcasting state
RemoteFunction	Client→Server	Yes (yields caller)	Client needs a result back (e.g. fetch inventory)
UnreliableRemoteEvent	Any direction	No	High-frequency updates where dropped packets are fine

Default to RemoteEvent. Avoid server→client RemoteFunction — an exploiter's frozen callback stalls your server thread indefinitely.

---

Where to Put Remotes

Always store Remotes in ReplicatedStorage. Create them from a server Script that runs before any LocalScript.

ReplicatedStorage/
  Remotes/
    DealDamage        (RemoteEvent)
    GetInventory      (RemoteFunction)
    SyncPosition      (UnreliableRemoteEvent)

-- Script in ServerScriptService
local folder = Instance.new("Folder")
folder.Name = "Remotes"
folder.Parent = game:GetService("ReplicatedStorage")

local function make(class, name)
    local r = Instance.new(class)
    r.Name = name
    r.Parent = folder
    return r
end

make("RemoteEvent",           "DealDamage")
make("RemoteFunction",        "GetInventory")
make("UnreliableRemoteEvent", "SyncPosition")

---

Firing Patterns

Client → Server (FireServer)

-- LocalScript
local DealDamage = game:GetService("ReplicatedStorage").Remotes:WaitForChild("DealDamage")
DealDamage:FireServer({ targetId = 12345, amount = 50 })
-- First arg on server is always the firing Player (injected automatically, cannot be spoofed)

-- Script (server) — VALIDATE everything in the payload
DealDamage.OnServerEvent:Connect(function(player, data)
    -- player identity is trustworthy; data contents are not
end)

Server → One Client

local Notify = game:GetService("ReplicatedStorage").Remotes:WaitForChild("Notify")
Notify:FireClient(player, { message = "Welcome!" })

-- LocalScript
Notify.OnClientEvent:Connect(function(data)
    print(data.message)
end)

Server → All Clients

AnnounceEvent:FireAllClients({ text = "Game starting in 10 seconds!" })

RemoteFunction (Client Calls, Server Returns)

-- Script (server)
GetInventory.OnServerInvoke = function(player)
    return getPlayerInventory(player.UserId)
end

-- LocalScript
local inventory = GetInventory:InvokeServer()  -- yields until server returns

UnreliableRemoteEvent (High-Frequency Sync)

-- LocalScript
RunService.Heartbeat:Connect(function()
    SyncPosition:FireServer(character.HumanoidRootPart.CFrame)
end)

-- Script (server) — still validate
SyncPosition.OnServerEvent:Connect(function(player, cframe)
    if typeof(cframe) ~= "CFrame" then return end
    -- apply with sanity bounds check
end)

---

CRITICAL: Server-Side Security

The client is hostile. Treat every argument as untrusted input.

local MAX_DAMAGE = 100
local COOLDOWNS = {}
local COOLDOWN_SECONDS = 0.5

DealDamage.OnServerEvent:Connect(function(player, data)
    -- 1. Rate limit
    local now = tick()
    if COOLDOWNS[player.UserId] and now - COOLDOWNS[player.UserId] < COOLDOWN_SECONDS then
        return
    end
    COOLDOWNS[player.UserId] = now

    -- 2. Type checks
    if type(data) ~= "table" then return end
    if type(data.targetId) ~= "number" then return end
    if type(data.amount) ~= "number" then return end

    -- 3. Range clamp
    local amount = math.clamp(data.amount, 0, MAX_DAMAGE)

    -- 4. Server-side weapon lookup — never trust client-provided Instance
    local weapon = getEquippedWeapon(player)
    if not weapon then return end

    -- 5. Server-side target lookup
    local target = getPlayerByUserId(data.targetId)
    if not target then return end

    applyDamage(target, amount, player)
end)

---

Exploit Patterns & Defenses

Exploit	What the attacker does	Defense
Argument injection	Sends unexpected types to crash handler	Type-check all arguments
Damage amplification	Sends amount = math.huge	Clamp to sane maximum
Remote spam	Fires thousands of times per second	Per-player cooldown
Spoofed target	Sends another player's UserId	Server resolves from its own state
Infinite yield	Never returns from OnClientEvent callback	Avoid server→client RemoteFunction
Duplicate action	Replays a valid fire to buy twice	Check state / consume token before acting

---

Quick Reference

FireServer(args)            LocalScript → server
FireClient(player, args)    server → one client
FireAllClients(args)        server → every client
InvokeServer(args)          LocalScript → server, waits for return
OnServerEvent               server-side listener for FireServer
OnClientEvent               client-side listener for FireClient/FireAllClients
OnServerInvoke              server-side function assigned for InvokeServer

---

Common Mistakes

Mistake	Fix
OnServerEvent in a LocalScript	Use OnClientEvent on client; OnServerEvent is server-only
Remotes in ServerStorage	Move to ReplicatedStorage
Trusting payload beyond player identity	Validate every field in the payload
Server→client RemoteFunction	Use RemoteEvent; frozen client stalls server thread
No WaitForChild in LocalScript	Remotes may not exist yet; always use WaitForChild
Multiple OnServerInvoke assignments	Only the last assignment wins; keep it in one place
Firing inside tight loop without throttle	Use UnreliableRemoteEvent or accumulate delta time