diff --git a/frontend/src/app/workspace/agents/[agent_name]/chats/[thread_id]/page.tsx b/frontend/src/app/workspace/agents/[agent_name]/chats/[thread_id]/page.tsx
index 6346891c3..8389a96b3 100644
--- a/frontend/src/app/workspace/agents/[agent_name]/chats/[thread_id]/page.tsx
+++ b/frontend/src/app/workspace/agents/[agent_name]/chats/[thread_id]/page.tsx
@@ -6,6 +6,7 @@ import { useCallback, useEffect, useState } from "react";
 
 import type { PromptInputMessage } from "@/components/ai-elements/prompt-input";
 import { Button } from "@/components/ui/button";
+import { SidebarTrigger } from "@/components/ui/sidebar";
 import { AgentWelcome } from "@/components/workspace/agent-welcome";
 import { ArtifactTrigger } from "@/components/workspace/artifacts";
 import { ChatBox, useThreadChat } from "@/components/workspace/chats";
@@ -168,33 +169,36 @@ export default function AgentChatPage() {
         <div className="relative flex size-full min-h-0 justify-between">
           <header
             className={cn(
-              "absolute top-0 right-0 left-0 z-30 flex h-12 shrink-0 items-center gap-2 px-4",
+              "absolute top-0 right-0 left-0 z-30 flex h-12 shrink-0 items-center gap-2 px-2 sm:px-4",
               isWelcomeMode
                 ? "bg-background/0 backdrop-blur-none"
                 : "bg-background/80 shadow-xs backdrop-blur",
             )}
           >
+            <SidebarTrigger className="md:hidden" />
             {/* Agent badge */}
-            <div className="flex shrink-0 items-center gap-1.5 rounded-md border px-2 py-1">
+            <div className="flex min-w-0 shrink-0 items-center gap-1.5 rounded-md border px-2 py-1">
               <BotIcon className="text-primary h-3.5 w-3.5" />
-              <span className="text-xs font-medium">
+              <span className="hidden max-w-24 truncate text-xs font-medium sm:inline sm:max-w-none">
                 {agent?.name ?? agent_name}
               </span>
             </div>
 
-            <div className="flex w-full items-center text-sm font-medium">
+            <div className="flex min-w-0 flex-1 items-center text-sm font-medium">
               <ThreadTitle threadId={threadId} thread={thread} />
             </div>
-            <div className="mr-4 flex items-center">
+            <div className="flex shrink-0 items-center sm:mr-4">
               <Tooltip content={t.agents.newChat}>
                 <Button
+                  className="px-2 sm:px-3"
                   size="sm"
                   variant="secondary"
                   onClick={() => {
                     router.push(`/workspace/agents/${agent_name}/chats/new`);
                   }}
                 >
-                  <PlusSquare /> {t.agents.newChat}
+                  <PlusSquare />
+                  <span className="hidden sm:inline">{t.agents.newChat}</span>
                 </Button>
               </Tooltip>
               <TokenUsageIndicator
@@ -229,14 +233,15 @@ export default function AgentChatPage() {
 
             <div
               className={cn(
-                "right-0 bottom-0 left-0 z-30 flex justify-center px-4",
+                "right-0 bottom-0 left-0 z-30 flex justify-center px-3 sm:px-4",
                 isWelcomeMode ? "absolute" : "relative shrink-0 pb-4",
               )}
             >
               <div
                 className={cn(
                   "relative w-full",
-                  isWelcomeMode && "-translate-y-[calc(50vh-96px)]",
+                  isWelcomeMode &&
+                    "-translate-y-[calc(50vh-48px)] sm:-translate-y-[calc(50vh-96px)]",
                   isWelcomeMode
                     ? "max-w-(--container-width-sm)"
                     : "max-w-(--container-width-md)",
@@ -267,7 +272,7 @@ export default function AgentChatPage() {
                 <InputBox
                   className={cn(
                     "bg-background/5 w-full",
-                    isWelcomeMode && "-translate-y-4",
+                    isWelcomeMode && "-translate-y-2 sm:-translate-y-4",
                   )}
                   isWelcomeMode={isWelcomeMode}
                   threadId={threadId}
diff --git a/frontend/src/app/workspace/chats/[thread_id]/page.tsx b/frontend/src/app/workspace/chats/[thread_id]/page.tsx
index 0c8ed87ef..3e3e93877 100644
--- a/frontend/src/app/workspace/chats/[thread_id]/page.tsx
+++ b/frontend/src/app/workspace/chats/[thread_id]/page.tsx
@@ -4,6 +4,7 @@ import { useRouter } from "next/navigation";
 import { useCallback, useEffect, useRef, useState } from "react";
 
 import { type PromptInputMessage } from "@/components/ai-elements/prompt-input";
+import { SidebarTrigger } from "@/components/ui/sidebar";
 import { ArtifactTrigger } from "@/components/workspace/artifacts";
 import {
   ChatBox,
@@ -170,16 +171,17 @@ export default function ChatPage() {
         <div className="relative flex size-full min-h-0 justify-between">
           <header
             className={cn(
-              "absolute top-0 right-0 left-0 z-30 flex h-12 shrink-0 items-center px-4",
+              "absolute top-0 right-0 left-0 z-30 flex h-12 shrink-0 items-center gap-2 px-2 sm:px-4",
               isWelcomeMode
                 ? "bg-background/0 backdrop-blur-none"
                 : "bg-background/80 shadow-xs backdrop-blur",
             )}
           >
-            <div className="flex w-full items-center text-sm font-medium">
+            <SidebarTrigger className="md:hidden" />
+            <div className="flex min-w-0 flex-1 items-center text-sm font-medium">
               <ThreadTitle threadId={threadId} thread={thread} />
             </div>
-            <div className="flex items-center gap-2">
+            <div className="flex shrink-0 items-center gap-2">
               <TokenUsageIndicator
                 threadId={isNewThread ? undefined : threadId}
                 backendUsage={backendTokenUsage}
@@ -210,14 +212,15 @@ export default function ChatPage() {
             </div>
             <div
               className={cn(
-                "right-0 bottom-0 left-0 z-30 flex justify-center px-4",
+                "right-0 bottom-0 left-0 z-30 flex justify-center px-3 sm:px-4",
                 isWelcomeMode ? "absolute" : "relative shrink-0 pb-4",
               )}
             >
               <div
                 className={cn(
                   "relative w-full",
-                  isWelcomeMode && "-translate-y-[calc(50vh-96px)]",
+                  isWelcomeMode &&
+                    "-translate-y-[calc(50vh-48px)] sm:-translate-y-[calc(50vh-96px)]",
                   isWelcomeMode
                     ? "max-w-(--container-width-sm)"
                     : "max-w-(--container-width-md)",
@@ -248,7 +251,7 @@ export default function ChatPage() {
                   <InputBox
                     className={cn(
                       "bg-background/5 w-full",
-                      isWelcomeMode && "-translate-y-4",
+                      isWelcomeMode && "-translate-y-2 sm:-translate-y-4",
                     )}
                     isWelcomeMode={isWelcomeMode}
                     threadId={threadId}
@@ -280,7 +283,7 @@ export default function ChatPage() {
                     aria-hidden="true"
                     className={cn(
                       "bg-background/5 h-32 w-full rounded-2xl",
-                      isWelcomeMode && "-translate-y-4",
+                      isWelcomeMode && "-translate-y-2 sm:-translate-y-4",
                     )}
                   />
                 )}
diff --git a/frontend/src/components/workspace/input-box.tsx b/frontend/src/components/workspace/input-box.tsx
index 6241016d5..ad28a4a88 100644
--- a/frontend/src/components/workspace/input-box.tsx
+++ b/frontend/src/components/workspace/input-box.tsx
@@ -582,7 +582,7 @@ export function InputBox({
     <div
       ref={promptRootRef}
       className={cn(
-        "relative flex flex-col",
+        "relative flex min-w-0 flex-col",
         isWelcomeMode ? "gap-4" : "gap-2",
       )}
     >
@@ -694,8 +694,8 @@ export function InputBox({
             ref={textareaRef}
           />
         </PromptInputBody>
-        <PromptInputFooter className="flex">
-          <PromptInputTools>
+        <PromptInputFooter className="flex flex-wrap gap-2 sm:flex-nowrap">
+          <PromptInputTools className="min-w-0 flex-1 flex-wrap">
             {/* TODO: Add more connectors here
           <PromptInputActionMenu>
             <PromptInputActionMenuTrigger className="px-2!" />
@@ -717,7 +717,7 @@ export function InputBox({
                     : "flash"
                 }
               >
-                <PromptInputActionMenuTrigger className="gap-1! px-2!">
+                <PromptInputActionMenuTrigger className="max-w-28 gap-1! px-2! sm:max-w-none">
                   <div>
                     {context.mode === "flash" && <ZapIcon className="size-3" />}
                     {context.mode === "thinking" && (
@@ -732,7 +732,7 @@ export function InputBox({
                   </div>
                   <div
                     className={cn(
-                      "text-xs font-normal",
+                      "truncate text-xs font-normal",
                       context.mode === "ultra" ? "golden-text" : "",
                     )}
                   >
@@ -879,7 +879,7 @@ export function InputBox({
             </PromptInputActionMenu>
             {supportReasoningEffort && context.mode !== "flash" && (
               <PromptInputActionMenu>
-                <PromptInputActionMenuTrigger className="gap-1! px-2!">
+                <PromptInputActionMenuTrigger className="hidden gap-1! px-2! sm:inline-flex">
                   <div className="text-xs font-normal">
                     {t.inputBox.reasoningEffort}:
                     {context.reasoning_effort === "minimal" &&
@@ -994,13 +994,13 @@ export function InputBox({
               </PromptInputActionMenu>
             )}
           </PromptInputTools>
-          <PromptInputTools>
+          <PromptInputTools className="min-w-0 justify-end">
             <ModelSelector
               open={modelDialogOpen}
               onOpenChange={setModelDialogOpen}
             >
               <ModelSelectorTrigger asChild>
-                <PromptInputButton>
+                <PromptInputButton className="max-w-40 min-w-0 sm:max-w-56">
                   <div className="flex min-w-0 flex-col items-start text-left">
                     <ModelSelectorName className="text-xs font-normal">
                       {selectedModel?.display_name}
@@ -1103,7 +1103,7 @@ function SuggestionList() {
     [textInput],
   );
   return (
-    <Suggestions className="min-h-16 w-fit items-start">
+    <Suggestions className="min-h-16 w-full max-w-full justify-center px-4 sm:w-fit sm:px-0">
       <ConfettiButton
         className="text-muted-foreground cursor-pointer rounded-full px-4 text-xs font-normal"
         variant="outline"
diff --git a/frontend/src/components/workspace/welcome.tsx b/frontend/src/components/workspace/welcome.tsx
index f737ae00c..a0a8d23ac 100644
--- a/frontend/src/components/workspace/welcome.tsx
+++ b/frontend/src/components/workspace/welcome.tsx
@@ -10,6 +10,14 @@ import { AuroraText } from "../ui/aurora-text";
 
 let waved = false;
 
+function WelcomeDescription({ children }: { children: string }) {
+  return (
+    <p className="max-w-full text-wrap break-words whitespace-pre-line">
+      {children}
+    </p>
+  );
+}
+
 export function Welcome({
   className,
   mode,
@@ -32,15 +40,15 @@ export function Welcome({
   return (
     <div
       className={cn(
-        "mx-auto flex w-full flex-col items-center justify-center gap-2 px-8 py-4 text-center",
+        "mx-auto flex w-full max-w-full flex-col items-center justify-center gap-2 px-4 py-4 text-center sm:px-8",
         className,
       )}
     >
-      <div className="text-2xl font-bold">
+      <div className="max-w-full text-2xl font-bold">
         {searchParams.get("mode") === "skill" ? (
           `✨ ${t.welcome.createYourOwnSkill} ✨`
         ) : (
-          <div className="flex items-center gap-2">
+          <div className="flex max-w-full flex-wrap items-center justify-center gap-2">
             <div className={cn("inline-block", !waved ? "animate-wave" : "")}>
               {isUltra ? "🚀" : "👋"}
             </div>
@@ -49,24 +57,14 @@ export function Welcome({
         )}
       </div>
       {searchParams.get("mode") === "skill" ? (
-        <div className="text-muted-foreground text-sm">
-          {t.welcome.createYourOwnSkillDescription.includes("\n") ? (
-            <pre className="font-sans whitespace-pre">
-              {t.welcome.createYourOwnSkillDescription}
-            </pre>
-          ) : (
-            <p>{t.welcome.createYourOwnSkillDescription}</p>
-          )}
+        <div className="text-muted-foreground max-w-full text-sm">
+          <WelcomeDescription>
+            {t.welcome.createYourOwnSkillDescription}
+          </WelcomeDescription>
         </div>
       ) : (
-        <div className="text-muted-foreground text-sm">
-          {t.welcome.description.includes("\n") ? (
-            <pre className="font-sans whitespace-pre">
-              {t.welcome.description}
-            </pre>
-          ) : (
-            <p>{t.welcome.description}</p>
-          )}
+        <div className="text-muted-foreground max-w-full text-sm">
+          <WelcomeDescription>{t.welcome.description}</WelcomeDescription>
         </div>
       )}
     </div>
diff --git a/frontend/src/components/workspace/workspace-container.tsx b/frontend/src/components/workspace/workspace-container.tsx
index 9dd547d74..e1e9c3b7d 100644
--- a/frontend/src/components/workspace/workspace-container.tsx
+++ b/frontend/src/components/workspace/workspace-container.tsx
@@ -12,6 +12,7 @@ import {
   BreadcrumbPage,
   BreadcrumbSeparator,
 } from "@/components/ui/breadcrumb";
+import { SidebarTrigger } from "@/components/ui/sidebar";
 import { useI18n } from "@/core/i18n/hooks";
 import { cn } from "@/lib/utils";
 
@@ -51,7 +52,8 @@ export function WorkspaceHeader({
       )}
       {...props}
     >
-      <div className="flex items-center gap-2 px-4">
+      <div className="flex min-w-0 items-center gap-2 px-2 sm:px-4">
+        <SidebarTrigger className="md:hidden" />
         <Breadcrumb>
           <BreadcrumbList>
             {segments?.[0] && (
diff --git a/frontend/tests/e2e/sidebar.spec.ts b/frontend/tests/e2e/sidebar.spec.ts
index 4aac9fa58..6bccf8f73 100644
--- a/frontend/tests/e2e/sidebar.spec.ts
+++ b/frontend/tests/e2e/sidebar.spec.ts
@@ -29,4 +29,45 @@ test.describe("Sidebar navigation", () => {
     await page.waitForURL("**/workspace/agents");
     await expect(page).toHaveURL(/\/workspace\/agents/);
   });
+
+  test("mobile welcome layout stays within viewport and opens sidebar", async ({
+    page,
+  }) => {
+    await page.setViewportSize({ width: 390, height: 844 });
+    mockLangGraphAPI(page);
+
+    await page.goto("/workspace/chats/new");
+
+    const viewportWidth = page.viewportSize()?.width ?? 390;
+    const expectInsideViewport = async (
+      locator: ReturnType<typeof page.locator>,
+    ) => {
+      await expect(locator).toBeVisible({ timeout: 15_000 });
+      const box = await locator.boundingBox();
+      expect(box).not.toBeNull();
+      expect(box!.x).toBeGreaterThanOrEqual(-1);
+      expect(box!.x + box!.width).toBeLessThanOrEqual(viewportWidth + 1);
+    };
+
+    await expectInsideViewport(page.getByText(/Welcome to|欢迎使用/).first());
+    await expectInsideViewport(page.getByRole("textbox").first());
+    await expectInsideViewport(page.locator("[data-slot='suggestions-list']"));
+
+    const mobileSidebarTrigger = page
+      .locator("[data-sidebar='trigger']:visible")
+      .first();
+    await expect(mobileSidebarTrigger).toBeVisible();
+    await mobileSidebarTrigger.click();
+
+    const mobileSidebar = page.locator(
+      "[data-mobile='true'][data-sidebar='sidebar']",
+    );
+    await expect(mobileSidebar).toBeVisible();
+    await expect(
+      mobileSidebar.locator("a[href='/workspace/chats']"),
+    ).toBeVisible();
+    await expect(
+      mobileSidebar.locator("a[href='/workspace/agents']"),
+    ).toBeVisible();
+  });
 });