How to make a Roblox dialogue system (with AI)

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8 files · 237 lines · one recipe call

Sample output: ServerScriptService/DialogServer

-- Dialog tree per NPC. Extend by adding more NPC keys with start/end nodes.
local TREES = {
	Sage = {
		start = {
			text = "Traveler. What brings you here?",
			replies = {
				{ text = "Tell me about this place.", next = "lore" },
				{ text = "I'm just passing through.", next = "leave" },
			},
		},
		lore = {
			text = "Wisdom lives here in old stones. Walk carefully near the lower halls.",
			replies = {
				{ text = "Thank you.", next = "leave" },
			},
		},
		leave = {
			text = "Walk safely.",
			["end"] = true,
		},
	},
}

local currentNode: { [number]: { npc: string, node: string } } = {}

local function getNode(npcName: string, nodeId: string)
	local tree = TREES[npcName]
	if not tree then return nil end
	return tree[nodeId]
end

local function buildResponse(npcName: string, nodeId: string)
	local node = getNode(npcName, nodeId)
	if not node then return { closed = true } end
	local clientReplies = {}
	if node.replies then
		for i, r in ipairs(node.replies) do
			table.insert(clientReplies, { index = i, text = r.text })
		end
	end
	return {
		npc = npcName,
		text = node.text,
		replies = clientReplies,
		ended = node["end"] == true,
	}
end

DialogStart.OnServerInvoke = function(player: Player, npcArg: any)
	-- Server validates input — never trusts client args
	if type(npcArg) ~= "string" then return { closed = true } end
	if not TREES[npcArg] then return { closed = true } end
	currentNode[player.UserId] = { npc = npcArg, node = "start" }
	return buildResponse(npcArg, "start")
end

DialogReply.OnServerInvoke = function(player: Player, replyIndexArg: any)
	local state = currentNode[player.UserId]
	if not state then return { closed = true } end
	if type(replyIndexArg) ~= "number" then return { closed = true } end

	local replyIndex = math.floor(replyIndexArg)
	local node = getNode(state.npc, state.node)
	if not node or not node.replies or not node.replies[replyIndex] then
		return { closed = true }
	end

	local nextId = node.replies[replyIndex].next
	if not nextId then return { closed = true } end

	local nextNode = getNode(state.npc, nextId)
	if not nextNode then return { closed = true } end

	currentNode[player.UserId] = { npc = state.npc, node = nextId }
	if nextNode["end"] then currentNode[player.UserId] = nil end

	return buildResponse(state.npc, nextId)
end