diff --git a/codemap/templates/viewer.html b/codemap/templates/viewer.html
new file mode 100644
index 0000000..a5eebec
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+++ b/codemap/templates/viewer.html
@@ -0,0 +1,147 @@
+<!DOCTYPE html>
+<html lang="en">
+<head>
+    <meta charset="UTF-8">
+    <meta name="viewport" content="width=device-width, initial-scale=1.0">
+    <title>{{ title }}</title>
+    <script type="module">
+        import mermaid from 'https://cdn.jsdelivr.net/npm/mermaid@10/dist/mermaid.esm.min.mjs';
+        mermaid.initialize({
+            startOnLoad: true,
+            theme: 'default',
+            securityLevel: 'loose',
+            flowchart: {
+                useMaxWidth: true,
+                htmlLabels: true,
+                curve: 'basis'
+            }
+        });
+    </script>
+    <style>
+        * {
+            margin: 0;
+            padding: 0;
+            box-sizing: border-box;
+        }
+        body {
+            font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, sans-serif;
+            background: linear-gradient(135deg, #1a1a2e 0%, #16213e 100%);
+            min-height: 100vh;
+            color: #e1e4e8;
+        }
+        .container {
+            max-width: 1400px;
+            margin: 0 auto;
+            padding: 20px;
+        }
+        header {
+            display: flex;
+            justify-content: space-between;
+            align-items: center;
+            padding: 20px 0;
+            border-bottom: 1px solid #30363d;
+            margin-bottom: 20px;
+        }
+        h1 {
+            font-size: 1.5rem;
+            font-weight: 600;
+            color: #58a6ff;
+        }
+        .controls {
+            display: flex;
+            gap: 10px;
+        }
+        button {
+            background: #238636;
+            color: white;
+            border: none;
+            padding: 8px 16px;
+            border-radius: 6px;
+            cursor: pointer;
+            font-size: 0.9rem;
+            transition: background 0.2s;
+        }
+        button:hover {
+            background: #2ea043;
+        }
+        .diagram-container {
+            background: #0d1117;
+            border-radius: 12px;
+            padding: 20px;
+            min-height: 600px;
+            border: 1px solid #30363d;
+        }
+        .mermaid {
+            display: flex;
+            justify-content: center;
+            align-items: center;
+            min-height: 500px;
+        }
+        .status {
+            padding: 10px 15px;
+            background: #161b22;
+            border-radius: 6px;
+            margin-top: 15px;
+            font-size: 0.85rem;
+            color: #8b949e;
+        }
+        .loading {
+            display: flex;
+            justify-content: center;
+            align-items: center;
+            height: 400px;
+            color: #8b949e;
+        }
+        .spinner {
+            width: 40px;
+            height: 40px;
+            border: 3px solid #30363d;
+            border-top-color: #58a6ff;
+            border-radius: 50%;
+            animation: spin 1s linear infinite;
+        }
+        @keyframes spin {
+            to { transform: rotate(360deg); }
+        }
+    </style>
+</head>
+<body>
+    <div class="container">
+        <header>
+            <h1>{{ title }}</h1>
+            <div class="controls">
+                <button onclick="window.print()">Export PDF</button>
+                <button onclick="downloadMermaid()">Download Mermaid</button>
+            </div>
+        </header>
+        <div class="diagram-container">
+            <div class="mermaid">
+{{ mermaid_content }}
+            </div>
+        </div>
+        <div class="status">
+            Last updated: <span id="timestamp"></span>
+        </div>
+    </div>
+    <script>
+        document.getElementById('timestamp').textContent = new Date().toLocaleString();
+
+        {% if auto_refresh %}
+        setInterval(function() {
+            location.reload();
+        }, {{ refresh_interval }} * 1000);
+        {% endif %}
+
+        function downloadMermaid() {
+            const content = `{{ mermaid_content }}`;
+            const blob = new Blob([content], { type: 'text/plain' });
+            const url = URL.createObjectURL(blob);
+            const a = document.createElement('a');
+            a.href = url;
+            a.download = 'diagram.mmd';
+            a.click();
+            URL.revokeObjectURL(url);
+        }
+    </script>
+</body>
+</html>
