Lync

Lync is a networking library for Roblox. You describe each packet, query and replicated set once, as a schema of codecs, and both the server and the client require that one module. A value sent from one side is decoded by the same definition on the other, and its Luau type is inferred from the schema, so handlers, records and replies are typed without annotations. Every value is packed at the bit, an int(0, 100) costs seven bits, and everything sent during a frame is batched into one remote call per client when you flush.

One namespace with all three primitives.

ReplicatedStorage/Net.luau

return Lync.define("arena", {
    Strike = Lync.packet(Lync.vec3(Lync.quant(-512, 512, 0.1))):unreliable(),

    Sell = Lync.query(
        Lync.struct({ item = Lync.enum({ "sword", "shield" }) }),
        Lync.struct({ earned = Lync.int(0, 1000000) })
    ),

    Fighters = Lync.replicate(Lync.struct({
        name  = Lync.str(1, 20),
        team  = Lync.enum({ "red", "blue" }),
        score = Lync.int(0, 1000000),
        pos   = Lync.vec3(Lync.quant(-512, 512, 0.1)):newest(10),
    })):keyBy("team"),
})

The server and client code for this namespace.

ServerClient

Net.Strike:onServer(function(position, player)
    resolveHit(player, position)
end)

Net.Sell:onServer(function(request, player)
    return { earned = price(request.item) }
end)

Net.Fighters:add(userId, { name = "Ada", team = "red", score = 0, pos = at })

Lync.start()
RunService.PostSimulation:Connect(function()
    Lync.flush()
end)

Net.Fighters:onChanged(function(id, record, old)
    board:set(id, record.score)
end)

Lync.start()
RunService.PostSimulation:Connect(function()
    Lync.flush()
end)

Net.Strike:fireServer(aim())

local ok, receipt = Net.Sell:request({ item = "sword" })
if ok then
    wallet:add(receipt.earned)
end

record.score and receipt.earned are typed as number without any annotation.

Setup	Installing, the shared definition module, wiring both sides.
Packets	One way messages, delivery modes, recipients.
Queries	Requests and replies, and how a request can end without one.
Sets	Server owned records replicated to the clients allowed to see them.
Codecs	Every value type and its size on the wire.