feat: warn users when too many MCP tools are enabled

apps/cli/src/types/constants.ts

@@ -1,4 +1,7 @@
-import { reasoningEffortsExtended } from "@roo-code/types"
+import { reasoningEffortsExtended, MAX_MCP_TOOLS_THRESHOLD } from "@roo-code/types"
+
+// Re-export for backward compatibility
+export { MAX_MCP_TOOLS_THRESHOLD }
 
 export const DEFAULT_FLAGS = {
 	mode: "code",

packages/types/src/mcp.ts

@@ -1,5 +1,11 @@
 import { z } from "zod"
 
+/**
+ * Maximum number of MCP tools that can be enabled before showing a warning.
+ * LLMs tend to perform poorly when given too many tools to choose from.
+ */
+export const MAX_MCP_TOOLS_THRESHOLD = 40
+
 /**
  * McpServerUse
  */

packages/types/src/message.ts

@@ -149,6 +149,7 @@ export function isNonBlockingAsk(ask: ClineAsk): ask is NonBlockingAsk {
  * - `condense_context`: Context condensation/summarization has started
  * - `condense_context_error`: Error occurred during context condensation
  * - `codebase_search_result`: Results from searching the codebase
+ * - `too_many_tools_warning`: Warning that too many MCP tools are enabled, which may confuse the LLM
  */
 export const clineSays = [
 	"error",
@@ -180,6 +181,7 @@ export const clineSays = [
 	"sliding_window_truncation",
 	"codebase_search_result",
 	"user_edit_todos",
+	"too_many_tools_warning",
 ] as const
 
 export const clineSaySchema = z.enum(clineSays)

src/core/task/Task.ts

@@ -53,6 +53,7 @@ import {
 	MIN_CHECKPOINT_TIMEOUT_SECONDS,
 	TOOL_PROTOCOL,
 	ConsecutiveMistakeError,
+	MAX_MCP_TOOLS_THRESHOLD,
 } from "@roo-code/types"
 import { TelemetryService } from "@roo-code/telemetry"
 import { CloudService, BridgeOrchestrator } from "@roo-code/cloud"
@@ -1832,6 +1833,59 @@ export class Task extends EventEmitter<TaskEvents> implements TaskLike {
 	// Lifecycle
 	// Start / Resume / Abort / Dispose
 
+	/**
+	 * Count the number of enabled MCP tools across all enabled and connected servers.
+	 * Returns the count along with the number of servers contributing.
+	 *
+	 * @returns Object with enabledToolCount and enabledServerCount
+	 */
+	private async countEnabledMcpTools(): Promise<{ enabledToolCount: number; enabledServerCount: number }> {
+		let serverCount = 0
+		let toolCount = 0
+
+		try {
+			const provider = this.providerRef.deref()
+			if (!provider) {
+				return { enabledToolCount: 0, enabledServerCount: 0 }
+			}
+
+			const { mcpEnabled } = (await provider.getState()) ?? {}
+			if (!(mcpEnabled ?? true)) {
+				return { enabledToolCount: 0, enabledServerCount: 0 }
+			}
+
+			const mcpHub = await McpServerManager.getInstance(provider.context, provider)
+			if (!mcpHub) {
+				return { enabledToolCount: 0, enabledServerCount: 0 }
+			}
+
+			const servers = mcpHub.getServers()
+			for (const server of servers) {
+				// Skip disabled servers
+				if (server.disabled) continue
+
+				// Skip servers that are not connected
+				if (server.status !== "connected") continue
+
+				serverCount++
+
+				// Count enabled tools on this server
+				if (server.tools) {
+					for (const tool of server.tools) {
+						// Tool is enabled if enabledForPrompt is undefined (default) or true
+						if (tool.enabledForPrompt !== false) {
+							toolCount++
+						}
+					}
+				}
+			}
+		} catch (error) {
+			console.error("[Task#countEnabledMcpTools] Error counting MCP tools:", error)
+		}
+
+		return { enabledToolCount: toolCount, enabledServerCount: serverCount }
+	}
+
 	private async startTask(task?: string, images?: string[]): Promise<void> {
 		if (this.enableBridge) {
 			try {
@@ -1858,6 +1912,24 @@ export class Task extends EventEmitter<TaskEvents> implements TaskLike {
 		await this.providerRef.deref()?.postStateToWebview()
 
 		await this.say("text", task, images)
+
+		// Check for too many MCP tools and warn the user
+		const { enabledToolCount, enabledServerCount } = await this.countEnabledMcpTools()
+		if (enabledToolCount > MAX_MCP_TOOLS_THRESHOLD) {
+			await this.say(
+				"too_many_tools_warning",
+				JSON.stringify({
+					toolCount: enabledToolCount,
+					serverCount: enabledServerCount,
+					threshold: MAX_MCP_TOOLS_THRESHOLD,
+				}),
+				undefined,
+				undefined,
+				undefined,
+				undefined,
+				{ isNonInteractive: true },
+			)
+		}
 		this.isInitialized = true
 
 		let imageBlocks: Anthropic.ImageBlockParam[] = formatResponse.imageBlocks(images)

webview-ui/src/components/chat/ChatRow.tsx

@@ -32,6 +32,7 @@ import { ReasoningBlock } from "./ReasoningBlock"
 import Thumbnails from "../common/Thumbnails"
 import ImageBlock from "../common/ImageBlock"
 import ErrorRow from "./ErrorRow"
+import WarningRow from "./WarningRow"
 
 import McpResourceRow from "../mcp/McpResourceRow"
 
@@ -1512,6 +1513,26 @@ export const ChatRowContent = ({
 				case "browser_action_result":
 					// Handled by BrowserSessionRow; prevent raw JSON (action/result) from rendering here
 					return null
+				case "too_many_tools_warning": {
+					const warningData = safeJsonParse<{
+						toolCount: number
+						serverCount: number
+						threshold: number
+					}>(message.text || "{}")
+					if (!warningData) return null
+					const toolsPart = t("chat:tooManyTools.toolsPart", { count: warningData.toolCount })
+					const serversPart = t("chat:tooManyTools.serversPart", { count: warningData.serverCount })
+					return (
+						<WarningRow
+							title={t("chat:tooManyTools.title")}
+							message={t("chat:tooManyTools.messageTemplate", {
+								tools: toolsPart,
+								servers: serversPart,
+								threshold: warningData.threshold,
+							})}
+						/>
+					)
+				}
 				default:
 					return (
 						<>

webview-ui/src/components/chat/ErrorRow.tsx

@@ -266,11 +266,11 @@ export const ErrorRow = memo(
 							</div>
 						</div>
 					)}
-					<div className="ml-2 pl-4 mt-1 pt-1 border-l border-vscode-errorForeground/50">
+					<div className="ml-2 pl-4 mt-1 pt-0.5 border-l border-vscode-errorForeground/50">
 						<p
 							className={
 								messageClassName ||
-								"my-0 font-light whitespace-pre-wrap break-words text-vscode-descriptionForeground"
+								"cursor-default my-0 font-light whitespace-pre-wrap break-words text-vscode-descriptionForeground"
 							}>
 							{message}
 							{formattedErrorDetails && (

webview-ui/src/components/chat/TooManyToolsWarning.tsx

@@ -0,0 +1,67 @@
+import React, { useMemo } from "react"
+import { useAppTranslation } from "@/i18n/TranslationContext"
+import { useExtensionState } from "@src/context/ExtensionStateContext"
+import { MAX_MCP_TOOLS_THRESHOLD } from "@roo-code/types"
+import WarningRow from "./WarningRow"
+
+// Re-export for backward compatibility
+export { MAX_MCP_TOOLS_THRESHOLD }
+
+/**
+ * Displays a warning when the user has too many MCP tools enabled.
+ * LLMs get confused when offered too many tools, which can lead to errors.
+ *
+ * The warning is shown when:
+ * - The total number of enabled tools across all enabled MCP servers exceeds the threshold
+ *
+ * @example
+ * <TooManyToolsWarning />
+ */
+export const TooManyToolsWarning: React.FC = () => {
+	const { t } = useAppTranslation()
+	const { mcpServers } = useExtensionState()
+
+	const { enabledServerCount, enabledToolCount } = useMemo(() => {
+		let serverCount = 0
+		let toolCount = 0
+
+		for (const server of mcpServers) {
+			// Skip disabled servers
+			if (server.disabled) continue
+
+			// Skip servers that are not connected
+			if (server.status !== "connected") continue
+
+			serverCount++
+
+			// Count enabled tools on this server
+			if (server.tools) {
+				for (const tool of server.tools) {
+					// Tool is enabled if enabledForPrompt is undefined (default) or true
+					if (tool.enabledForPrompt !== false) {
+						toolCount++
+					}
+				}
+			}
+		}
+
+		return { enabledServerCount: serverCount, enabledToolCount: toolCount }
+	}, [mcpServers])
+
+	// Don't show warning if under threshold
+	if (enabledToolCount <= MAX_MCP_TOOLS_THRESHOLD) {
+		return null
+	}
+
+	const toolsPart = t("chat:tooManyTools.toolsPart", { count: enabledToolCount })
+	const serversPart = t("chat:tooManyTools.serversPart", { count: enabledServerCount })
+	const message = t("chat:tooManyTools.messageTemplate", {
+		tools: toolsPart,
+		servers: serversPart,
+		threshold: MAX_MCP_TOOLS_THRESHOLD,
+	})
+
+	return <WarningRow title={t("chat:tooManyTools.title")} message={message} />
+}
+
+export default TooManyToolsWarning

webview-ui/src/components/chat/WarningRow.tsx

@@ -0,0 +1,57 @@
+import React from "react"
+import { TriangleAlert, BookOpenText } from "lucide-react"
+import { useAppTranslation } from "@/i18n/TranslationContext"
+import { vscode } from "@src/utils/vscode"
+
+export interface WarningRowProps {
+	title: string
+	message: string
+	docsURL?: string
+}
+
+/**
+ * A generic warning row component that displays a warning icon, title, and message.
+ * Optionally includes a documentation link.
+ *
+ * @param title - The warning title displayed in bold
+ * @param message - The warning message displayed below the title
+ * @param docsURL - Optional documentation link URL (shown as "Learn more" with book icon)
+ *
+ * @example
+ * <WarningRow
+ *   title="Too many tools enabled"
+ *   message="You have 50 tools enabled via 5 MCP servers."
+ *   docsURL="https://docs.example.com/mcp-best-practices"
+ * />
+ */
+export const WarningRow: React.FC<WarningRowProps> = ({ title, message, docsURL }) => {
+	const { t } = useAppTranslation()
+
+	return (
+		<div className="group pr-2 py-2">
+			<div className="flex items-center justify-between gap-2 break-words">
+				<TriangleAlert className="w-4 text-vscode-editorWarning-foreground shrink-0" />
+				<span className="font-bold text-vscode-editorWarning-foreground grow cursor-default">{title}</span>
+				{docsURL && (
+					<a
+						href={docsURL}
+						className="text-sm flex items-center gap-1 transition-opacity opacity-0 group-hover:opacity-100"
+						onClick={(e) => {
+							e.preventDefault()
+							vscode.postMessage({ type: "openExternal", url: docsURL })
+						}}>
+						<BookOpenText className="size-3 mt-[3px]" />
+						{t("chat:apiRequest.errorMessage.docs")}
+					</a>
+				)}
+			</div>
+			<div className="cursor-default ml-2 pl-4 mt-1 pt-0.5 border-l border-vscode-editorWarning-foreground/50">
+				<p className="my-0 font-light whitespace-pre-wrap break-words text-vscode-descriptionForeground">
+					{message}
+				</p>
+			</div>
+		</div>
+	)
+}
+
+export default WarningRow