feat: add disableTaskLists option to mode configuration

- Add optional disableTaskLists property to ModeConfig type schema
- Update tool description generation to conditionally exclude update_todo_list tool
- Modify isToolAllowedForMode to respect disableTaskLists setting
- Add comprehensive tests for the new functionality

Fixes #5693

packages/types/src/mode.ts

@@ -70,6 +70,7 @@ export const modeConfigSchema = z.object({
 	customInstructions: z.string().optional(),
 	groups: groupEntryArraySchema,
 	source: z.enum(["global", "project"]).optional(),
+	disableTaskLists: z.boolean().optional(),
 })
 
 export type ModeConfig = z.infer<typeof modeConfigSchema>

src/core/prompts/tools/__tests__/index.spec.ts

@@ -0,0 +1,119 @@
+// npx vitest run src/core/prompts/tools/__tests__/index.spec.ts
+
+import type { ModeConfig } from "@roo-code/types"
+
+import { getToolDescriptionsForMode } from "../index"
+
+describe("getToolDescriptionsForMode", () => {
+	describe("disableTaskLists", () => {
+		it("excludes update_todo_list from tool descriptions when disableTaskLists is true", () => {
+			const customModes: ModeConfig[] = [
+				{
+					slug: "no-tasks-mode",
+					name: "No Tasks Mode",
+					roleDefinition: "A mode without task lists",
+					groups: ["read"] as const,
+					disableTaskLists: true,
+				},
+			]
+
+			const toolDescriptions = getToolDescriptionsForMode(
+				"no-tasks-mode",
+				"/test/cwd",
+				false, // supportsComputerUse
+				undefined, // codeIndexManager
+				undefined, // diffStrategy
+				undefined, // browserViewportSize
+				undefined, // mcpHub
+				customModes,
+				{}, // experiments
+				false, // partialReadsEnabled
+				{}, // settings
+			)
+
+			// Should not contain update_todo_list tool description
+			expect(toolDescriptions).not.toContain("update_todo_list")
+			expect(toolDescriptions).not.toContain("## update_todo_list")
+
+			// Should still contain other always available tools
+			expect(toolDescriptions).toContain("ask_followup_question")
+			expect(toolDescriptions).toContain("attempt_completion")
+		})
+
+		it("includes update_todo_list in tool descriptions when disableTaskLists is false", () => {
+			const customModes: ModeConfig[] = [
+				{
+					slug: "tasks-mode",
+					name: "Tasks Mode",
+					roleDefinition: "A mode with task lists",
+					groups: ["read"] as const,
+					disableTaskLists: false,
+				},
+			]
+
+			const toolDescriptions = getToolDescriptionsForMode(
+				"tasks-mode",
+				"/test/cwd",
+				false, // supportsComputerUse
+				undefined, // codeIndexManager
+				undefined, // diffStrategy
+				undefined, // browserViewportSize
+				undefined, // mcpHub
+				customModes,
+				{}, // experiments
+				false, // partialReadsEnabled
+				{}, // settings
+			)
+
+			// Should contain update_todo_list tool description
+			expect(toolDescriptions).toContain("## update_todo_list")
+		})
+
+		it("includes update_todo_list in tool descriptions when disableTaskLists is undefined", () => {
+			const customModes: ModeConfig[] = [
+				{
+					slug: "default-mode",
+					name: "Default Mode",
+					roleDefinition: "A mode with default task list behavior",
+					groups: ["read"] as const,
+				},
+			]
+
+			const toolDescriptions = getToolDescriptionsForMode(
+				"default-mode",
+				"/test/cwd",
+				false, // supportsComputerUse
+				undefined, // codeIndexManager
+				undefined, // diffStrategy
+				undefined, // browserViewportSize
+				undefined, // mcpHub
+				customModes,
+				{}, // experiments
+				false, // partialReadsEnabled
+				{}, // settings
+			)
+
+			// Should contain update_todo_list tool description by default
+			expect(toolDescriptions).toContain("## update_todo_list")
+		})
+
+		it("includes update_todo_list in built-in mode tool descriptions", () => {
+			const toolDescriptions = getToolDescriptionsForMode(
+				"code",
+				"/test/cwd",
+				false, // supportsComputerUse
+				undefined, // codeIndexManager
+				undefined, // diffStrategy
+				undefined, // browserViewportSize
+				undefined, // mcpHub
+				[], // customModes
+				{}, // experiments
+				false, // partialReadsEnabled
+				{}, // settings
+			)
+
+			// Built-in modes should always include update_todo_list
+			expect(toolDescriptions).toContain("## update_todo_list")
+		})
+	})
+})

src/core/prompts/tools/index.ts

@@ -98,8 +98,14 @@ export function getToolDescriptionsForMode(
 		}
 	})
 
-	// Add always available tools
-	ALWAYS_AVAILABLE_TOOLS.forEach((tool) => tools.add(tool))
+	// Add always available tools, but check for mode-specific exclusions
+	ALWAYS_AVAILABLE_TOOLS.forEach((tool) => {
+		// Check if update_todo_list should be excluded for this mode
+		if (tool === "update_todo_list" && config.disableTaskLists) {
+			return // Skip adding this tool
+		}
+		tools.add(tool)
+	})
 
 	// Conditionally exclude codebase_search if feature is disabled or not configured
 	if (

src/core/tools/__tests__/validateToolUse.spec.ts

@@ -128,6 +128,59 @@ describe("mode-validator", () => {
 				expect(isToolAllowedForMode("apply_diff", codeMode, [], requirements)).toBe(false)
 			})
 		})
+
+		describe("disableTaskLists", () => {
+			it("disallows update_todo_list when disableTaskLists is true", () => {
+				const customModes: ModeConfig[] = [
+					{
+						slug: "no-tasks-mode",
+						name: "No Tasks Mode",
+						roleDefinition: "A mode without task lists",
+						groups: ["read"] as const,
+						disableTaskLists: true,
+					},
+				]
+				// Should not allow update_todo_list tool
+				expect(isToolAllowedForMode("update_todo_list", "no-tasks-mode", customModes)).toBe(false)
+				// Should still allow other always available tools
+				expect(isToolAllowedForMode("ask_followup_question", "no-tasks-mode", customModes)).toBe(true)
+				expect(isToolAllowedForMode("attempt_completion", "no-tasks-mode", customModes)).toBe(true)
+			})
+
+			it("allows update_todo_list when disableTaskLists is false", () => {
+				const customModes: ModeConfig[] = [
+					{
+						slug: "tasks-mode",
+						name: "Tasks Mode",
+						roleDefinition: "A mode with task lists",
+						groups: ["read"] as const,
+						disableTaskLists: false,
+					},
+				]
+				// Should allow update_todo_list tool
+				expect(isToolAllowedForMode("update_todo_list", "tasks-mode", customModes)).toBe(true)
+			})
+
+			it("allows update_todo_list when disableTaskLists is undefined", () => {
+				const customModes: ModeConfig[] = [
+					{
+						slug: "default-mode",
+						name: "Default Mode",
+						roleDefinition: "A mode with default task list behavior",
+						groups: ["read"] as const,
+					},
+				]
+				// Should allow update_todo_list tool by default
+				expect(isToolAllowedForMode("update_todo_list", "default-mode", customModes)).toBe(true)
+			})
+
+			it("allows update_todo_list in built-in modes", () => {
+				// Built-in modes should always allow update_todo_list
+				expect(isToolAllowedForMode("update_todo_list", codeMode, [])).toBe(true)
+				expect(isToolAllowedForMode("update_todo_list", architectMode, [])).toBe(true)
+				expect(isToolAllowedForMode("update_todo_list", askMode, [])).toBe(true)
+			})
+		})
 	})
 
 	describe("validateToolUse", () => {

src/shared/modes.ts

@@ -231,8 +231,15 @@ export function isToolAllowedForMode(
 	toolParams?: Record<string, any>, // All tool parameters
 	experiments?: Record<string, boolean>,
 ): boolean {
-	// Always allow these tools
+	// Always allow these tools, but check for mode-specific exclusions
 	if (ALWAYS_AVAILABLE_TOOLS.includes(tool as any)) {
+		// Check if update_todo_list should be excluded for this mode
+		if (tool === "update_todo_list") {
+			const mode = getModeBySlug(modeSlug, customModes)
+			if (mode?.disableTaskLists) {
+				return false
+			}
+		}
 		return true
 	}
 	if (experiments && Object.values(EXPERIMENT_IDS).includes(tool as ExperimentId)) {