diff --git a/src/constants/prompts.ts b/src/constants/prompts.ts
index 49755d8a74..fabaa146bb 100644
--- a/src/constants/prompts.ts
+++ b/src/constants/prompts.ts
@@ -20,6 +20,7 @@ import { TASK_CREATE_TOOL_NAME } from '@claude-code-best/builtin-tools/tools/Tas
 import type { Tools } from '../Tool.js'
 import type { Command } from '../types/command.js'
 import { BASH_TOOL_NAME } from '@claude-code-best/builtin-tools/tools/BashTool/toolName.js'
+import { POWERSHELL_TOOL_NAME } from '@claude-code-best/builtin-tools/tools/PowerShellTool/toolName.js'
 import {
   getCanonicalName,
   getMarketingNameForModel,
@@ -273,8 +274,20 @@ function getUsingYourToolsSection(enabledTools: Set<string>): string {
     return [`# Using your tools`, ...prependBullets(items)].join(`\n`)
   }
 
+  const hasPowerShell = enabledTools.has(POWERSHELL_TOOL_NAME)
+  const hasBash = enabledTools.has(BASH_TOOL_NAME)
+  const shellToolGuidance = hasPowerShell
+    ? hasBash
+      ? `On Windows, prefer the ${POWERSHELL_TOOL_NAME} tool for terminal operations (git, npm, docker, builds, tests, system commands). Use ${BASH_TOOL_NAME} only when the user asks for bash/Git Bash or a command is clearly bash-only. Prefer dedicated tools over shell equivalents (e.g., ${FILE_READ_TOOL_NAME} over Get-Content/cat, ${FILE_EDIT_TOOL_NAME} over sed, ${GLOB_TOOL_NAME} over find, ${GREP_TOOL_NAME} over grep/Select-String).`
+      : `Prefer dedicated tools over ${POWERSHELL_TOOL_NAME} equivalents (e.g., ${FILE_READ_TOOL_NAME} over Get-Content, ${FILE_EDIT_TOOL_NAME} over (Get-Content) -replace, ${GLOB_TOOL_NAME} over Get-ChildItem -Recurse, ${GREP_TOOL_NAME} over Select-String). Reserve ${POWERSHELL_TOOL_NAME} for shell operations: package installs, test runners, build commands, git operations.`
+    : `Prefer dedicated tools over ${BASH_TOOL_NAME} equivalents (e.g., ${FILE_READ_TOOL_NAME} over cat, ${FILE_EDIT_TOOL_NAME} over sed, ${GLOB_TOOL_NAME} over find, ${GREP_TOOL_NAME} over grep). Reserve ${BASH_TOOL_NAME} for shell operations: package installs, test runners, build commands, git operations.`
+
+  const coreToolsList = hasPowerShell
+    ? `Core tools (Read, Edit, Write, Glob, Grep, ${POWERSHELL_TOOL_NAME}${hasBash ? `, ${BASH_TOOL_NAME}` : ''}, Agent, WebFetch, WebSearch, AskUserQuestion, NotebookEdit, TaskCreate, TaskUpdate, TaskList, TaskGet, TodoWrite, Skill, CronCreate, CronDelete, CronList, Config, LSP, MCPTool) can be called directly as needed. ${shellToolGuidance}`
+    : `Core tools (Read, Edit, Write, Glob, Grep, Bash, Agent, WebFetch, WebSearch, AskUserQuestion, NotebookEdit, TaskCreate, TaskUpdate, TaskList, TaskGet, TodoWrite, Skill, CronCreate, CronDelete, CronList, Config, LSP, MCPTool) can be called directly as needed. ${shellToolGuidance}`
+
   const items = [
-    `Core tools (Read, Edit, Write, Glob, Grep, Bash, Agent, WebFetch, WebSearch, AskUserQuestion, NotebookEdit, TaskCreate, TaskUpdate, TaskList, TaskGet, TodoWrite, Skill, CronCreate, CronDelete, CronList, Config, LSP, MCPTool) can be called directly as needed. Prefer dedicated tools over ${BASH_TOOL_NAME} equivalents (e.g., ${FILE_READ_TOOL_NAME} over cat, ${FILE_EDIT_TOOL_NAME} over sed, ${GLOB_TOOL_NAME} over find, ${GREP_TOOL_NAME} over grep). Reserve ${BASH_TOOL_NAME} for shell operations: package installs, test runners, build commands, git operations.`,
+    coreToolsList,
     `Search before saying unknown — when the user references a file, function, or module you have not seen, search with ${GREP_TOOL_NAME}/${GLOB_TOOL_NAME} first.`,
     taskToolName
       ? `Break down and manage your work with the ${taskToolName} tool. Mark each task as completed as soon as you are done.`
diff --git a/src/services/tips/tipRegistry.ts b/src/services/tips/tipRegistry.ts
index 6afa145747..d7672e5088 100644
--- a/src/services/tips/tipRegistry.ts
+++ b/src/services/tips/tipRegistry.ts
@@ -238,11 +238,12 @@ const externalTips: Tip[] = [
   {
     id: 'powershell-tool-env',
     content: async () =>
-      'Set CLAUDE_CODE_USE_POWERSHELL_TOOL=1 to enable the PowerShell tool (preview)',
-    cooldownSessions: 10,
+      'PowerShell is the default shell on Windows. Set CLAUDE_CODE_USE_POWERSHELL_TOOL=0 or defaultShell=bash to prefer Bash/Git Bash instead.',
+    cooldownSessions: 20,
     isRelevant: async () =>
       getPlatform() === 'windows' &&
-      process.env.CLAUDE_CODE_USE_POWERSHELL_TOOL === undefined,
+      process.env.CLAUDE_CODE_USE_POWERSHELL_TOOL === undefined &&
+      getSettings_DEPRECATED().defaultShell === undefined,
   },
   {
     id: 'status-line',
diff --git a/src/utils/settings/types.ts b/src/utils/settings/types.ts
index 6125911fd1..dbdbd4c61b 100644
--- a/src/utils/settings/types.ts
+++ b/src/utils/settings/types.ts
@@ -460,13 +460,13 @@ export const SettingsSchema = lazySchema(() =>
         .boolean()
         .optional()
         .describe('Disable all hooks and statusLine execution'),
-      // Which shell backs input-box `!` (see docs/design/ps-shell-selection.md §4.2)
+      // Which shell backs input-box `!` (see resolveDefaultShell)
       defaultShell: z
         .enum(['bash', 'powershell'])
         .optional()
         .describe(
           'Default shell for input-box ! commands. ' +
-            "Defaults to 'bash' on all platforms (no Windows auto-flip).",
+            "Defaults to 'powershell' on Windows when the PowerShell tool is enabled, otherwise 'bash'. Set explicitly to override.",
         ),
       // Only run hooks defined in managed settings (managed-settings.json)
       allowManagedHooksOnly: z
diff --git a/src/utils/shell/__tests__/shellDefaults.windows.test.ts b/src/utils/shell/__tests__/shellDefaults.windows.test.ts
new file mode 100644
index 0000000000..3fe1306178
--- /dev/null
+++ b/src/utils/shell/__tests__/shellDefaults.windows.test.ts
@@ -0,0 +1,73 @@
+/**
+ * Windows default shell: PowerShell tool on by default; ! routing prefers it.
+ */
+import { afterEach, beforeEach, describe, expect, mock, test } from 'bun:test'
+
+const settingsState: { defaultShell?: 'bash' | 'powershell' } = {}
+
+mock.module('src/utils/settings/settings.js', () => ({
+  getInitialSettings: () => ({ ...settingsState }),
+}))
+
+// Force windows platform for these unit tests regardless of host OS.
+mock.module('src/utils/platform.js', () => ({
+  getPlatform: () => 'windows' as const,
+  SUPPORTED_PLATFORMS: ['macos', 'wsl'],
+}))
+
+import { isPowerShellToolEnabled } from '../shellToolUtils.js'
+import { resolveDefaultShell } from '../resolveDefaultShell.js'
+
+const ENV_KEY = 'CLAUDE_CODE_USE_POWERSHELL_TOOL'
+let savedEnv: string | undefined
+
+beforeEach(() => {
+  savedEnv = process.env[ENV_KEY]
+  delete process.env[ENV_KEY]
+  delete settingsState.defaultShell
+})
+
+afterEach(() => {
+  if (savedEnv === undefined) delete process.env[ENV_KEY]
+  else process.env[ENV_KEY] = savedEnv
+  delete settingsState.defaultShell
+})
+
+describe('isPowerShellToolEnabled (windows)', () => {
+  test('enabled by default when env unset', () => {
+    expect(isPowerShellToolEnabled()).toBe(true)
+  })
+
+  test('disabled when env is falsy', () => {
+    process.env[ENV_KEY] = '0'
+    expect(isPowerShellToolEnabled()).toBe(false)
+    process.env[ENV_KEY] = 'false'
+    expect(isPowerShellToolEnabled()).toBe(false)
+  })
+
+  test('enabled when env is truthy', () => {
+    process.env[ENV_KEY] = '1'
+    expect(isPowerShellToolEnabled()).toBe(true)
+  })
+})
+
+describe('resolveDefaultShell (windows)', () => {
+  test('defaults to powershell when tool enabled and no settings', () => {
+    expect(resolveDefaultShell()).toBe('powershell')
+  })
+
+  test('honors settings.defaultShell=bash', () => {
+    settingsState.defaultShell = 'bash'
+    expect(resolveDefaultShell()).toBe('bash')
+  })
+
+  test('honors settings.defaultShell=powershell', () => {
+    settingsState.defaultShell = 'powershell'
+    expect(resolveDefaultShell()).toBe('powershell')
+  })
+
+  test('falls back to bash when PowerShell tool is disabled', () => {
+    process.env[ENV_KEY] = '0'
+    expect(resolveDefaultShell()).toBe('bash')
+  })
+})
diff --git a/src/utils/shell/resolveDefaultShell.ts b/src/utils/shell/resolveDefaultShell.ts
index fd6dd3da56..0897226288 100644
--- a/src/utils/shell/resolveDefaultShell.ts
+++ b/src/utils/shell/resolveDefaultShell.ts
@@ -1,14 +1,25 @@
 import { getInitialSettings } from '../settings/settings.js'
+import { getPlatform } from '../platform.js'
+import { isPowerShellToolEnabled } from './shellToolUtils.js'
 
 /**
- * Resolve the default shell for input-box `!` commands.
+ * Resolve the default shell for input-box `!` commands and agent preference.
  *
- * Resolution order (docs/design/ps-shell-selection.md §4.2):
- *   settings.defaultShell → 'bash'
+ * Resolution order:
+ *   1. settings.defaultShell (explicit user/project setting)
+ *   2. Windows + PowerShell tool enabled → 'powershell'
+ *   3. otherwise → 'bash'
  *
- * Platform default is 'bash' everywhere — we do NOT auto-flip Windows to
- * PowerShell (would break existing Windows users with bash hooks).
+ * Opt out of the Windows PowerShell default via settings.defaultShell=bash
+ * or CLAUDE_CODE_USE_POWERSHELL_TOOL=0 (disables the PowerShell tool entirely).
  */
 export function resolveDefaultShell(): 'bash' | 'powershell' {
-  return getInitialSettings().defaultShell ?? 'bash'
+  const configured = getInitialSettings().defaultShell
+  if (configured === 'bash' || configured === 'powershell') {
+    return configured
+  }
+  if (getPlatform() === 'windows' && isPowerShellToolEnabled()) {
+    return 'powershell'
+  }
+  return 'bash'
 }
diff --git a/src/utils/shell/shellToolUtils.ts b/src/utils/shell/shellToolUtils.ts
index b11cb40550..099a71242f 100644
--- a/src/utils/shell/shellToolUtils.ts
+++ b/src/utils/shell/shellToolUtils.ts
@@ -1,14 +1,16 @@
 import { BASH_TOOL_NAME } from '@claude-code-best/builtin-tools/tools/BashTool/toolName.js'
 import { POWERSHELL_TOOL_NAME } from '@claude-code-best/builtin-tools/tools/PowerShellTool/toolName.js'
-import { isEnvDefinedFalsy, isEnvTruthy } from '../envUtils.js'
+import { isEnvDefinedFalsy } from '../envUtils.js'
 import { getPlatform } from '../platform.js'
 
 export const SHELL_TOOL_NAMES: string[] = [BASH_TOOL_NAME, POWERSHELL_TOOL_NAME]
 
 /**
  * Runtime gate for PowerShellTool. Windows-only (the permission engine uses
- * Win32-specific path normalizations). Ant defaults on (opt-out via env=0);
- * external defaults off (opt-in via env=1).
+ * Win32-specific path normalizations).
+ *
+ * Default: ON on Windows for all builds (opt-out via
+ * CLAUDE_CODE_USE_POWERSHELL_TOOL=0 / false / off). Non-Windows always off.
  *
  * Used by tools.ts (tool-list visibility), processBashCommand (! routing),
  * and promptShellExecution (skill frontmatter routing) so the gate is
@@ -16,7 +18,5 @@ export const SHELL_TOOL_NAMES: string[] = [BASH_TOOL_NAME, POWERSHELL_TOOL_NAME]
  */
 export function isPowerShellToolEnabled(): boolean {
   if (getPlatform() !== 'windows') return false
-  return process.env.USER_TYPE === 'ant'
-    ? !isEnvDefinedFalsy(process.env.CLAUDE_CODE_USE_POWERSHELL_TOOL)
-    : isEnvTruthy(process.env.CLAUDE_CODE_USE_POWERSHELL_TOOL)
+  return !isEnvDefinedFalsy(process.env.CLAUDE_CODE_USE_POWERSHELL_TOOL)
 }