Your first query

A query is a client-to-server request that returns a response. Use it when the caller cannot continue without a server result.

Before you start

Complete Required initialization first. Your shared namespace module must be required on both the server and client.

1. Define request and response types

ReplicatedStorage/Network.luau

local ReplicatedStorage = game:GetService("ReplicatedStorage")
local ByteNetMax = require(ReplicatedStorage.ByteNetMax)

return ByteNetMax.defineNamespace("PlayerData", function()
    return {
        queries = {
            GetItemCount = ByteNetMax.defineQuery({
                request = ByteNetMax.struct({
                    ItemId = ByteNetMax.string,
                }),
                response = ByteNetMax.uint16,
            }),
        },
    }
end)

2. Return the response on the server

ServerScriptService/Network.server.luau

local ReplicatedStorage = game:GetService("ReplicatedStorage")
local Network = require(ReplicatedStorage.Network)

Network.queries.GetItemCount.listen(function(Request, Player)
    -- Replace this with a lookup in server-owned player data.
    local Inventory = GetInventoryFor(Player)
    return Inventory[Request.ItemId] or 0
end)

The returned value must match the query's response data type.

3. Invoke it on the client

StarterPlayerScripts/Network.client.luau

local ReplicatedStorage = game:GetService("ReplicatedStorage")
local Network = require(ReplicatedStorage.Network)

local PotionCount = Network.queries.GetItemCount.invoke({
    ItemId = "HealthPotion",
})

print(`Potions: {PotionCount}`)

invoke yields until the server responds. Do not invoke a query every frame or use one for fire-and-forget notifications.

No request data?

Use request = ByteNetMax.nothing, then call invoke(nil).

Understand query behavior