diff --git a/entrypoints/content/email-helper.css b/entrypoints/content/email-helper.css
index 75074bdc..6eb1d8f0 100644
--- a/entrypoints/content/email-helper.css
+++ b/entrypoints/content/email-helper.css
@@ -263,11 +263,36 @@ input.gmail-alias-input-preview::placeholder {
   color: #2563eb;
 }
 
+.gmail-alias-popup-user-guide {
+  position: relative;
+  display: flex;
+  width: 28px;
+  height: 28px;
+  box-sizing: border-box;
+  align-items: center;
+  justify-content: center;
+  padding: 0;
+  border: 1px solid #bfdbfe;
+  border-radius: 7px;
+  background: #eff6ff;
+  color: #2563eb;
+  cursor: pointer;
+  text-decoration: none;
+}
+
+.gmail-alias-popup-user-guide:hover,
+.gmail-alias-popup-user-guide:focus-visible {
+  border-color: #93c5fd;
+  background: #dbeafe;
+  color: #1d4ed8;
+  outline: none;
+}
 .gmail-alias-popup-disable-site {
   position: relative;
   display: flex;
   width: 28px;
   height: 28px;
+  box-sizing: border-box;
   align-items: center;
   justify-content: center;
   padding: 0;
@@ -284,6 +309,7 @@ input.gmail-alias-input-preview::placeholder {
   color: #b91c1c;
 }
 
+.gmail-alias-popup-user-guide::after,
 .gmail-alias-popup-disable-site::after {
   position: absolute;
   z-index: 2;
@@ -310,6 +336,8 @@ input.gmail-alias-input-preview::placeholder {
   white-space: normal;
 }
 
+.gmail-alias-popup-user-guide:hover::after,
+.gmail-alias-popup-user-guide:focus-visible::after,
 .gmail-alias-popup-disable-site:hover::after,
 .gmail-alias-popup-disable-site:focus-visible::after {
   opacity: 1;
diff --git a/entrypoints/content/index.ts b/entrypoints/content/index.ts
index 563da141..7e82a788 100644
--- a/entrypoints/content/index.ts
+++ b/entrypoints/content/index.ts
@@ -5,6 +5,7 @@ import {
   parseDisabledInlineSites,
 } from "src/utils/inlineSiteSettings";
 import { t } from "../../lib/i18n";
+import { USER_GUIDE_URL } from "src/utils/externalLinks";
 import {
   getPreviousAliasForWebsite,
   generateSuggestionsForWebsite,
@@ -240,12 +241,20 @@ function createPopup(
     nextPage: escapeHtml(t("nextPage")),
     disableInlineForSite: escapeHtml(t("disableInlineForSite")),
     extensionName: escapeHtml(t("extensionName")),
+    userGuide: escapeHtml(t("userGuide")),
     reportReview: escapeHtml(t("reportReview")),
   };
   popup.innerHTML = `
     <div class="gmail-alias-popup-header" style="display: flex; justify-content: space-between; align-items: center; padding: 12px 16px; border-bottom: 1px solid #e5e7eb; background: #f9fafb; border-radius: 8px 8px 0 0;">
       <span class="gmail-alias-popup-title" title="${safeWebsite}" style="font-weight: 600; font-size: 13px; color: #374151;">${labels.extensionName}</span>
       <div class="gmail-alias-popup-header-actions" style="display: flex; align-items: center; gap: 6px;">
+        <a class="gmail-alias-popup-user-guide" href="${USER_GUIDE_URL}" target="_blank" rel="noopener noreferrer" data-tooltip="${labels.userGuide}" aria-label="${labels.userGuide}">
+          <svg viewBox="0 0 24 24" width="16" height="16" aria-hidden="true" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round">
+            <circle cx="12" cy="12" r="10" />
+            <path d="M9.1 9a3 3 0 1 1 5.83 1c0 2-3 2-3 4" />
+            <path d="M12 18h.01" />
+          </svg>
+        </a>
         <button class="gmail-alias-popup-disable-site" type="button" data-tooltip="${labels.disableInlineForSite}" aria-label="${labels.disableInlineForSite}">
           <svg viewBox="0 0 24 24" width="16" height="16" aria-hidden="true" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round">
             <path d="M2 12s3.5-6 10-6 10 6 10 6-3.5 6-10 6S2 12 2 12Z" />
diff --git a/public/_locales/de/messages.json b/public/_locales/de/messages.json
index ea2e7529..453b4d53 100644
--- a/public/_locales/de/messages.json
+++ b/public/_locales/de/messages.json
@@ -770,5 +770,8 @@
   },
   "storageError": {
     "message": "Verlauf konnte nicht geladen werden. Überprüfen Sie den Speicherzugriff."
+  },
+  "userGuide": {
+    "message": "Benutzerhandbuch"
   }
 }
diff --git a/public/_locales/en/messages.json b/public/_locales/en/messages.json
index ed76b117..71349424 100644
--- a/public/_locales/en/messages.json
+++ b/public/_locales/en/messages.json
@@ -736,12 +736,24 @@
   "noTagsYet": {
     "message": "No tags yet"
   },
-  "disableInlineForSite": { "message": "Turn off the inline helper on this website" },
-  "inlineDisabledSites": { "message": "Disabled inline helper sites" },
-  "inlineDisabledSitesDescription": { "message": "The inline icon and quick popup are hidden on these websites." },
-  "noDisabledSites": { "message": "No disabled websites" },
-  "enableInlineForSite": { "message": "Enable" },
-  "reportReview": { "message": "Report / Review" },
+  "disableInlineForSite": {
+    "message": "Turn off the inline helper on this website"
+  },
+  "inlineDisabledSites": {
+    "message": "Disabled inline helper sites"
+  },
+  "inlineDisabledSitesDescription": {
+    "message": "The inline icon and quick popup are hidden on these websites."
+  },
+  "noDisabledSites": {
+    "message": "No disabled websites"
+  },
+  "enableInlineForSite": {
+    "message": "Enable"
+  },
+  "reportReview": {
+    "message": "Report / Review"
+  },
   "percentLabel": {
     "message": "$PERCENT$%",
     "placeholders": {
@@ -758,5 +770,8 @@
   },
   "storageError": {
     "message": "Failed to load history. Check storage access."
+  },
+  "userGuide": {
+    "message": "User guide"
   }
 }
diff --git a/public/_locales/es/messages.json b/public/_locales/es/messages.json
index b889e62c..1d0fd13d 100644
--- a/public/_locales/es/messages.json
+++ b/public/_locales/es/messages.json
@@ -770,5 +770,8 @@
   },
   "storageError": {
     "message": "No se pudo cargar el historial. Verifique el acceso al almacenamiento."
+  },
+  "userGuide": {
+    "message": "Guía del usuario"
   }
 }
diff --git a/public/_locales/fr/messages.json b/public/_locales/fr/messages.json
index c1ecb7ac..14d3131f 100644
--- a/public/_locales/fr/messages.json
+++ b/public/_locales/fr/messages.json
@@ -770,5 +770,8 @@
   },
   "storageError": {
     "message": "Impossible de charger l'historique. Vérifiez l'accès au stockage."
+  },
+  "userGuide": {
+    "message": "Guide d’utilisation"
   }
 }
diff --git a/public/_locales/hi/messages.json b/public/_locales/hi/messages.json
index 1eb9dc64..78641eeb 100644
--- a/public/_locales/hi/messages.json
+++ b/public/_locales/hi/messages.json
@@ -770,5 +770,8 @@
   },
   "storageError": {
     "message": "इतिहास लोड नहीं हो सका। संग्रहण पहुंच की जांच करें।"
+  },
+  "userGuide": {
+    "message": "उपयोगकर्ता मार्गदर्शिका"
   }
 }
diff --git a/public/_locales/it/messages.json b/public/_locales/it/messages.json
index 6814024e..3290c6b4 100644
--- a/public/_locales/it/messages.json
+++ b/public/_locales/it/messages.json
@@ -770,5 +770,8 @@
   },
   "storageError": {
     "message": "Impossibile caricare la cronologia. Verificare l'accesso all'archivio."
+  },
+  "userGuide": {
+    "message": "Guida utente"
   }
 }
diff --git a/public/_locales/ja/messages.json b/public/_locales/ja/messages.json
index e1ec2517..319eb41f 100644
--- a/public/_locales/ja/messages.json
+++ b/public/_locales/ja/messages.json
@@ -770,5 +770,8 @@
   },
   "storageError": {
     "message": "履歴を読み込めませんでした。ストレージアクセスを確認してください。"
+  },
+  "userGuide": {
+    "message": "ユーザーガイド"
   }
 }
diff --git a/public/_locales/ko/messages.json b/public/_locales/ko/messages.json
index cd785f6e..4027d12d 100644
--- a/public/_locales/ko/messages.json
+++ b/public/_locales/ko/messages.json
@@ -770,5 +770,8 @@
   },
   "storageError": {
     "message": "기록을 로드할 수 없습니다. 저장소 접근을 확인하세요."
+  },
+  "userGuide": {
+    "message": "사용자 가이드"
   }
 }
diff --git a/public/_locales/pl/messages.json b/public/_locales/pl/messages.json
index 30ed7769..4ed5e449 100644
--- a/public/_locales/pl/messages.json
+++ b/public/_locales/pl/messages.json
@@ -770,5 +770,8 @@
   },
   "storageError": {
     "message": "Nie udało się załadować historii. Sprawdź dostęp do pamięci."
+  },
+  "userGuide": {
+    "message": "Podręcznik użytkownika"
   }
 }
diff --git a/public/_locales/pt_BR/messages.json b/public/_locales/pt_BR/messages.json
index 745db700..1a9b7045 100644
--- a/public/_locales/pt_BR/messages.json
+++ b/public/_locales/pt_BR/messages.json
@@ -770,5 +770,8 @@
   },
   "storageError": {
     "message": "Falha ao carregar o histórico. Verifique o acesso ao armazenamento."
+  },
+  "userGuide": {
+    "message": "Guia do usuário"
   }
 }
diff --git a/public/_locales/ru/messages.json b/public/_locales/ru/messages.json
index 34df8490..4fa3c92a 100644
--- a/public/_locales/ru/messages.json
+++ b/public/_locales/ru/messages.json
@@ -770,5 +770,8 @@
   },
   "storageError": {
     "message": "Не удалось загрузить историю. Проверьте доступ к хранилищу."
+  },
+  "userGuide": {
+    "message": "Руководство пользователя"
   }
 }
diff --git a/public/_locales/tr/messages.json b/public/_locales/tr/messages.json
index c527b7b7..5a59c0a8 100644
--- a/public/_locales/tr/messages.json
+++ b/public/_locales/tr/messages.json
@@ -770,5 +770,8 @@
   },
   "storageError": {
     "message": "Geçmiş yüklenemedi. Depolama erişimini kontrol edin."
+  },
+  "userGuide": {
+    "message": "Kullanım kılavuzu"
   }
 }
diff --git a/public/_locales/vi/messages.json b/public/_locales/vi/messages.json
index b17f8aae..adc13e4a 100644
--- a/public/_locales/vi/messages.json
+++ b/public/_locales/vi/messages.json
@@ -770,5 +770,8 @@
   },
   "storageError": {
     "message": "Không thể tải lịch sử. Kiểm tra quyền truy cập bộ nhớ."
+  },
+  "userGuide": {
+    "message": "Hướng dẫn sử dụng"
   }
 }
diff --git a/public/_locales/zh_CN/messages.json b/public/_locales/zh_CN/messages.json
index f8cdb90b..a6699994 100644
--- a/public/_locales/zh_CN/messages.json
+++ b/public/_locales/zh_CN/messages.json
@@ -770,5 +770,8 @@
   },
   "storageError": {
     "message": "无法加载历史记录。请检查存储访问权限。"
+  },
+  "userGuide": {
+    "message": "用户指南"
   }
 }
diff --git a/src/components/alias/PopupHeader.tsx b/src/components/alias/PopupHeader.tsx
index 1a7ab46d..767f8c55 100644
--- a/src/components/alias/PopupHeader.tsx
+++ b/src/components/alias/PopupHeader.tsx
@@ -1,8 +1,9 @@
 // skipcq: JS-0415 - Header markup is a compact visual composition with no nested business logic.
-import { Settings, Sparkles } from "lucide-react";
+import { CircleHelp, Settings, Sparkles } from "lucide-react";
 import { Button } from "src/components/motion/button/base";
 import { Tooltip } from "src/components/motion/tooltip";
 import { ThemeToggle } from "src/components/motion/theme-toggle";
+import { openUserGuide } from "src/utils/externalLinks";
 import { t } from "../../../lib/i18n";
 
 export interface PopupHeaderProps {
@@ -37,12 +38,21 @@ interface HeaderActionsProps {
   onThemeChange: (theme: "light" | "dark") => void;
 }
 
-/** Header actions for theme switching and opening settings. */
+/** Opens the public user guide and contains any unexpected navigation error. */
+function handleOpenUserGuide() {
+  void openUserGuide().catch((error) => {
+    console.error("Failed to open the Gmail Alias Toolkit user guide.", error);
+  });
+}
+
+/** Header actions for theme switching, help, and opening settings. */
 function HeaderActions({
   isDark,
   onOpenSettings,
   onThemeChange,
 }: HeaderActionsProps) {
+  const userGuideLabel = t("userGuide");
+
   return (
     <div className="flex shrink-0 items-center gap-1.5">
       <Tooltip
@@ -61,6 +71,17 @@ function HeaderActions({
           iconClassName="h-4 w-4"
         />
       </Tooltip>
+      <Tooltip content={userGuideLabel} side="bottom">
+        <Button
+          onClick={handleOpenUserGuide}
+          variant="ghost"
+          size="icon"
+          className="shrink-0 rounded-2xl text-primary-foreground hover:bg-primary-foreground/15 focus-visible:ring-primary-foreground/60"
+          aria-label={userGuideLabel}
+        >
+          <CircleHelp className="h-5 w-5" aria-hidden="true" />
+        </Button>
+      </Tooltip>
       <Tooltip content={t("settings")} side="bottom">
         <Button
           onClick={onOpenSettings}
diff --git a/src/utils/externalLinks.ts b/src/utils/externalLinks.ts
new file mode 100644
index 00000000..8737903d
--- /dev/null
+++ b/src/utils/externalLinks.ts
@@ -0,0 +1,27 @@
+export const USER_GUIDE_URL =
+  "https://ext.eplus.dev/gmail-alias-toolkit/introduction?utm_source=gmail-alias-toolkit&utm_medium=extension&utm_campaign=user-guide";
+
+/** Opens the guide through a regular window when the tabs API is unavailable. */
+function openUserGuideWindow(): boolean {
+  try {
+    const openedWindow = globalThis.open?.(
+      USER_GUIDE_URL,
+      "_blank",
+      "noopener,noreferrer",
+    );
+    if (openedWindow) openedWindow.opener = null;
+    return Boolean(openedWindow);
+  } catch {
+    return false;
+  }
+}
+
+/** Opens the public Gmail Alias Toolkit guide with a safe browser fallback. */
+export async function openUserGuide(): Promise<boolean> {
+  try {
+    await browser.tabs.create({ url: USER_GUIDE_URL });
+    return true;
+  } catch {
+    return openUserGuideWindow();
+  }
+}
diff --git a/tests/i18n/userGuideLocales.test.ts b/tests/i18n/userGuideLocales.test.ts
new file mode 100644
index 00000000..4a24b634
--- /dev/null
+++ b/tests/i18n/userGuideLocales.test.ts
@@ -0,0 +1,48 @@
+import { type Dirent, readdirSync, readFileSync } from "node:fs";
+import { resolve } from "node:path";
+import { describe, expect, it } from "vitest";
+
+/** Returns whether a locale directory entry is a directory. */
+function isLocaleDirectory(entry: Dirent): boolean {
+  return entry.isDirectory();
+}
+
+/** Verifies that every WXT locale defines a non-empty user guide label. */
+function assertUserGuideMessages(): void {
+  const localesRoot = resolve(process.cwd(), "public/_locales");
+  const localeDirectories = readdirSync(localesRoot, {
+    withFileTypes: true,
+  }).filter(isLocaleDirectory);
+
+  expect(localeDirectories.length).toBeGreaterThan(0);
+
+  for (const locale of localeDirectories) {
+    const messagesPath = resolve(
+      localesRoot,
+      locale.name,
+      "messages.json",
+    );
+    const messages = JSON.parse(readFileSync(messagesPath, "utf8")) as Record<
+      string,
+      { message?: unknown } | undefined
+    >;
+    const userGuideMessage = messages.userGuide?.message;
+
+    expect(messages.userGuide, locale.name).toBeDefined();
+    expect(userGuideMessage, locale.name).toEqual(expect.any(String));
+    expect(
+      typeof userGuideMessage === "string" ? userGuideMessage.trim() : "",
+      locale.name,
+    ).not.toBe("");
+  }
+}
+
+/** Registers the WXT user guide localization regression test. */
+function defineUserGuideLocaleSuite(): void {
+  it(
+    "defines a non-empty userGuide message for every locale",
+    assertUserGuideMessages,
+  );
+}
+
+describe("WXT user guide translations", defineUserGuideLocaleSuite);
diff --git a/tests/utils/externalLinks.test.ts b/tests/utils/externalLinks.test.ts
new file mode 100644
index 00000000..9d4557a5
--- /dev/null
+++ b/tests/utils/externalLinks.test.ts
@@ -0,0 +1,50 @@
+import { afterEach, describe, expect, it, vi } from "vitest";
+import {
+  openUserGuide,
+  USER_GUIDE_URL,
+} from "../../src/utils/externalLinks";
+
+describe("external links", () => {
+  afterEach(() => {
+    vi.restoreAllMocks();
+    vi.unstubAllGlobals();
+  });
+
+  it("opens the tracked user guide URL in a browser tab", async () => {
+    const create = vi.fn().mockResolvedValue(undefined);
+    vi.stubGlobal("browser", { tabs: { create } });
+
+    await expect(openUserGuide()).resolves.toBe(true);
+
+    expect(create).toHaveBeenCalledWith({ url: USER_GUIDE_URL });
+    expect(USER_GUIDE_URL).toContain(
+      "https://ext.eplus.dev/gmail-alias-toolkit/introduction",
+    );
+    expect(USER_GUIDE_URL).toContain("utm_medium=extension");
+  });
+
+  it("falls back to a regular window when the tabs API rejects", async () => {
+    const create = vi.fn().mockRejectedValue(new Error("tabs unavailable"));
+    const openedWindow = { opener: {} };
+    const open = vi.fn().mockReturnValue(openedWindow);
+    vi.stubGlobal("browser", { tabs: { create } });
+    vi.stubGlobal("open", open);
+
+    await expect(openUserGuide()).resolves.toBe(true);
+
+    expect(open).toHaveBeenCalledWith(
+      USER_GUIDE_URL,
+      "_blank",
+      "noopener,noreferrer",
+    );
+    expect(openedWindow.opener).toBeNull();
+  });
+
+  it("returns false when neither navigation method is available", async () => {
+    const create = vi.fn().mockRejectedValue(new Error("tabs unavailable"));
+    vi.stubGlobal("browser", { tabs: { create } });
+    vi.stubGlobal("open", vi.fn().mockReturnValue(null));
+
+    await expect(openUserGuide()).resolves.toBe(false);
+  });
+});