diff --git a/src/components/headline-tree.tsx b/src/components/headline-tree.tsx
index 1245e12..b671509 100644
--- a/src/components/headline-tree.tsx
+++ b/src/components/headline-tree.tsx
@@ -4,7 +4,12 @@ import { useState } from "react";
 import { Badge } from "@/components/ui/badge";
 import type { HeadlineNode } from "@/app/actions";
 import { KeywordHighlighter } from "./keyword-highlighter";
-import { ChevronDown, ChevronsUp, ChevronsDown } from "lucide-react";
+import {
+  ChevronDown,
+  ChevronsUp,
+  ChevronsDown,
+  AlertTriangle,
+} from "lucide-react";
 import { cn } from "@/lib/utils";
 import { Button } from "@/components/ui/button";
 import {
@@ -36,6 +41,13 @@ const getCollapsiblePaths = (
   return paths;
 };
 
+const HierarchyWarning = ({ message }: { message: string }) => (
+  <div className="flex items-center gap-3 p-4 text-sm text-destructive-foreground bg-destructive/80 border-b">
+    <AlertTriangle className="h-5 w-5 flex-shrink-0" />
+    <p className="font-medium">{message}</p>
+  </div>
+);
+
 const HeadlineNodeDisplay = ({
   node,
   level,
@@ -43,49 +55,79 @@ const HeadlineNodeDisplay = ({
   keyword,
   collapsedStates,
   onToggle,
+  parentLevel,
+  isDuplicateH1,
 }: {
   node: HeadlineNode;
   level: number;
-  path: string;
+  path:string;
   keyword?: string | null;
   collapsedStates: Record<string, boolean>;
   onToggle: (path: string) => void;
+  parentLevel: number;
+  isDuplicateH1: boolean;
 }) => {
   const isCollapsible =
     node.level === 2 && node.children && node.children.length > 0;
   const isCollapsed = collapsedStates[path];
 
+  const levelSkipped = parentLevel > 0 && node.level > parentLevel + 1;
+  const hasError = isDuplicateH1 || levelSkipped;
+
+  let errorTooltip: string | null = null;
+  if (isDuplicateH1) {
+    errorTooltip = "Duplicate H1 tag. Only one H1 is recommended per page.";
+  } else if (levelSkipped) {
+    errorTooltip = `Incorrect hierarchy. An H${node.level} should not directly follow an H${parentLevel}.`;
+  }
+
+  const content = (
+    <div
+      className={cn(
+        "flex items-center gap-3 py-2.5 pr-4 border-t",
+        isCollapsible && "cursor-pointer hover:bg-muted/50",
+        hasError && "bg-destructive/10"
+      )}
+      style={{ paddingLeft: `${16 + level * 24}px` }}
+      onClick={() => isCollapsible && onToggle(path)}
+    >
+      <Badge
+        variant={hasError ? "destructive" : "secondary"}
+        className="uppercase w-12 flex-shrink-0 justify-center font-mono"
+      >
+        {node.tag}
+      </Badge>
+      <p className="font-medium flex-grow text-foreground">
+        <KeywordHighlighter text={node.text} keyword={keyword} />
+      </p>
+      <p className="text-sm text-muted-foreground flex-shrink-0 w-10 text-right">
+        {node.length}
+      </p>
+      {isCollapsible && (
+        <ChevronDown
+          className={cn(
+            "h-4 w-4 text-muted-foreground transition-transform",
+            !isCollapsed && "rotate-180"
+          )}
+        />
+      )}
+    </div>
+  );
+
   return (
     <>
-      <div
-        className={cn(
-          "flex items-center gap-3 py-2.5 pr-4 border-t",
-          isCollapsible && "cursor-pointer hover:bg-muted/50"
-        )}
-        style={{ paddingLeft: `${16 + level * 24}px` }}
-        onClick={() => isCollapsible && onToggle(path)}
-      >
-        <Badge
-          variant="secondary"
-          className="uppercase w-12 flex-shrink-0 justify-center font-mono"
-        >
-          {node.tag}
-        </Badge>
-        <p className="font-medium flex-grow text-foreground">
-          <KeywordHighlighter text={node.text} keyword={keyword} />
-        </p>
-        <p className="text-sm text-muted-foreground flex-shrink-0 w-10 text-right">
-          {node.length}
-        </p>
-        {isCollapsible && (
-          <ChevronDown
-            className={cn(
-              "h-4 w-4 text-muted-foreground transition-transform",
-              !isCollapsed && "rotate-180"
-            )}
-          />
-        )}
-      </div>
+      {errorTooltip ? (
+        <TooltipProvider>
+          <Tooltip>
+            <TooltipTrigger asChild>{content}</TooltipTrigger>
+            <TooltipContent>
+              <p>{errorTooltip}</p>
+            </TooltipContent>
+          </Tooltip>
+        </TooltipProvider>
+      ) : (
+        content
+      )}
       {node.children &&
         (!isCollapsible || !isCollapsed) &&
         node.children.map((child, index) => (
@@ -97,6 +139,8 @@ const HeadlineNodeDisplay = ({
             keyword={keyword}
             collapsedStates={collapsedStates}
             onToggle={onToggle}
+            parentLevel={node.level}
+            isDuplicateH1={false}
           />
         ))}
     </>
@@ -139,9 +183,17 @@ export function HeadlineTree({ headlines, keyword }: HeadlineTreeProps) {
   };
 
   const hasCollapsibleNodes = Object.keys(collapsedStates).length > 0;
+  const h1Count = headlines.filter((h) => h.tag === "h1").length;
+  const firstH1Index = headlines.findIndex((h) => h.tag === "h1");
 
   return (
     <div className="w-full rounded-lg overflow-hidden">
+      {h1Count === 0 && (
+        <HierarchyWarning message="No H1 tag found. Every page should have exactly one H1." />
+      )}
+      {h1Count > 1 && (
+        <HierarchyWarning message="Multiple H1 tags found. Only one H1 is recommended per page." />
+      )}
       {hasCollapsibleNodes && (
         <div className="flex items-center justify-between p-4 border-b bg-muted/50">
           <h4 className="font-semibold text-sm text-muted-foreground">
@@ -197,6 +249,8 @@ export function HeadlineTree({ headlines, keyword }: HeadlineTreeProps) {
             keyword={keyword}
             collapsedStates={collapsedStates}
             onToggle={handleToggle}
+            parentLevel={0}
+            isDuplicateH1={headline.tag === "h1" && index !== firstH1Index}
           />
         ))}
       </div>