diff --git a/README.md b/README.md
index 29ce349..042a17d 100644
--- a/README.md
+++ b/README.md
@@ -66,6 +66,7 @@ How markdown-proxy compares to other Markdown viewing tools:
   - Print: browser print with clean filename (toolbar hidden in print output)
   - Source: link to original URL on remote server (remote pages only)
 - Multiple CSS themes (GitHub, Simple, Dark) with switching UI
+- Table of contents sidebar: toggle `TOC` in the toolbar to open a right-side panel with auto-extracted headings; visibility persists per browser (localStorage)
 - Live reload for local files (auto-refreshes browser on file changes)
 - Directory listing for local files
 - Line anchor links: `[text](foo.md:12)` or `<a href="foo.md:12">` links navigate to specific source lines with highlighting (Markdown and text files)
diff --git a/internal/template/template.go b/internal/template/template.go
index edc2f9d..7f99c93 100644
--- a/internal/template/template.go
+++ b/internal/template/template.go
@@ -87,6 +87,7 @@ const markdownPageTplHead = `<!DOCTYPE html>
 <style>` + darkCSS + `</style>
 <style>` + commonCSS + `</style>
 <style>` + lineAnchorCSS + `</style>
+<style>` + tocCSS + `</style>
 `
 
 const markdownPageTplTail = `<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/katex@0.16.11/dist/katex.min.css">
@@ -99,6 +100,7 @@ const markdownPageTplTail = `<link rel="stylesheet" href="https://cdn.jsdelivr.n
   <div class="toolbar-actions">
     {{if .SourceURL}}<a href="{{.SourceURL}}" target="_blank" rel="noopener" class="toolbar-link">Source</a>{{end}}
     <a href="javascript:void(0)" onclick="printPage()" class="toolbar-link">Print</a>
+    <a href="javascript:void(0)" class="toolbar-link toc-toggle">TOC</a>
     <div class="theme-switcher">
       <label>Theme:</label>
       <select onchange="switchTheme(this.value)">
@@ -112,6 +114,10 @@ const markdownPageTplTail = `<link rel="stylesheet" href="https://cdn.jsdelivr.n
 <div class="markdown-body">
 {{.Content}}
 </div>
+<aside id="toc-panel" class="toc-panel">
+  <div class="toc-header">Table of Contents</div>
+  <div class="toc-body"><ul class="toc-list"></ul></div>
+</aside>
 <script>
 mermaid.initialize({startOnLoad: true, theme: document.body.className.includes('dark') ? 'dark' : 'default'});
 function printPage() {
@@ -149,6 +155,7 @@ document.addEventListener('DOMContentLoaded', function() {
 });
 </script>
 ` + lineAnchorJS + `
+` + tocJS + `
 {{if .WatchPath}}
 <script>
 (function() {
diff --git a/internal/template/toc.go b/internal/template/toc.go
new file mode 100644
index 0000000..21744e1
--- /dev/null
+++ b/internal/template/toc.go
@@ -0,0 +1,258 @@
+package template
+
+const tocCSS = `
+.markdown-body h1, .markdown-body h2, .markdown-body h3,
+.markdown-body h4, .markdown-body h5, .markdown-body h6 {
+  scroll-margin-top: 50px;
+}
+.toc-panel {
+  position: fixed;
+  top: 41px;
+  right: 0;
+  width: 280px;
+  height: calc(100vh - 41px);
+  overflow-y: auto;
+  border-left: 1px solid #e1e4e8;
+  background: #f6f8fa;
+  transform: translateX(100%);
+  transition: transform 0.2s ease-out;
+  z-index: 90;
+  font-size: 13px;
+}
+body.toc-visible .toc-panel { transform: translateX(0); }
+body.toc-visible .markdown-body { margin-right: 280px; }
+.toc-header {
+  padding: 10px 16px;
+  border-bottom: 1px solid #e1e4e8;
+  font-weight: bold;
+}
+.toc-body { padding: 8px 0; }
+.toc-list, .toc-list ul {
+  list-style: none;
+  padding-left: 0;
+  margin: 0;
+}
+.toc-list ul { padding-left: 14px; display: none; }
+.toc-list li.open > ul { display: block; }
+.toc-list li { margin: 0; position: relative; }
+.toc-list .toc-row {
+  display: flex;
+  align-items: flex-start;
+}
+.toc-list .toc-caret {
+  flex: 0 0 16px;
+  cursor: pointer;
+  user-select: none;
+  text-align: center;
+  line-height: 27px;
+  color: #6a737d;
+  font-size: 10px;
+}
+.toc-list .toc-caret::before { content: '\25B6'; }
+.toc-list li.open > .toc-row > .toc-caret::before { content: '\25BC'; }
+.toc-list .toc-caret.empty { visibility: hidden; }
+.toc-list a {
+  flex: 1;
+  display: block;
+  padding: 4px 16px 4px 4px;
+  text-decoration: none;
+  color: inherit;
+  border-left: 2px solid transparent;
+  word-break: break-word;
+}
+.toc-list a:hover { background: rgba(0,0,0,0.05); }
+.toc-list a.active {
+  border-left-color: #0366d6;
+  background: rgba(3,102,214,0.08);
+  font-weight: 600;
+}
+.toc-toggle.disabled {
+  opacity: 0.4;
+  pointer-events: none;
+}
+.theme-dark .toc-panel {
+  background: #161b22;
+  border-left-color: #30363d;
+}
+.theme-dark .toc-header { border-bottom-color: #30363d; }
+.theme-dark .toc-list a:hover { background: rgba(255,255,255,0.08); }
+.theme-dark .toc-list .toc-caret { color: #8b949e; }
+.theme-dark .toc-list a.active {
+  border-left-color: #58a6ff;
+  background: rgba(88,166,255,0.12);
+}
+.theme-simple .toc-panel {
+  background: #f5f5f5;
+  border-left-color: #ddd;
+}
+.theme-simple .toc-header { border-bottom-color: #ddd; }
+.theme-simple .toc-list a.active {
+  border-left-color: #07c;
+  background: rgba(0,119,204,0.08);
+}
+@media (max-width: 900px) {
+  body.toc-visible .markdown-body { margin-right: 0; }
+  .toc-panel { box-shadow: -2px 0 8px rgba(0,0,0,0.15); }
+}
+@media print {
+  .toc-panel, .toc-toggle { display: none !important; }
+  body.toc-visible .markdown-body { margin-right: 0 !important; }
+}
+`
+
+const tocJS = `<script>
+(function() {
+  var STORAGE_KEY = 'mdproxy_toc_visible';
+  var toggleBtn = document.querySelector('.toc-toggle');
+  var panel = document.getElementById('toc-panel');
+  if (!toggleBtn || !panel) return;
+
+  var headings = Array.prototype.slice.call(document.querySelectorAll(
+    '.markdown-body h1, .markdown-body h2, .markdown-body h3, .markdown-body h4, .markdown-body h5, .markdown-body h6'
+  ));
+  if (headings.length === 0) {
+    toggleBtn.classList.add('disabled');
+    toggleBtn.setAttribute('title', 'No headings in this document');
+    return;
+  }
+
+  var listRoot = panel.querySelector('.toc-list');
+
+  // Assign IDs and determine top level (smallest tag number).
+  var topLevel = 6;
+  headings.forEach(function(h, i) {
+    if (!h.id) h.id = 'toc-' + i;
+    var level = parseInt(h.tagName.substring(1), 10);
+    if (level < topLevel) topLevel = level;
+  });
+  // Initially expand items whose children are at level <= topLevel + 1.
+  var initialOpenThreshold = topLevel + 1;
+
+  // Build nested tree. Each stack entry represents a heading whose li may host
+  // deeper children; the ul under it is created lazily on first child.
+  var linkByHeading = new Map();
+  var liByHeading = new Map();
+  var stack = [{ level: topLevel - 1, ul: listRoot, li: null }];
+
+  headings.forEach(function(h) {
+    var level = parseInt(h.tagName.substring(1), 10);
+    while (stack.length > 1 && stack[stack.length - 1].level >= level) {
+      stack.pop();
+    }
+    var parent = stack[stack.length - 1];
+    if (!parent.ul) {
+      parent.ul = document.createElement('ul');
+      parent.li.appendChild(parent.ul);
+    }
+    var li = document.createElement('li');
+    var row = document.createElement('div');
+    row.className = 'toc-row';
+    var caret = document.createElement('span');
+    caret.className = 'toc-caret empty';
+    var a = document.createElement('a');
+    a.href = '#' + h.id;
+    a.textContent = h.textContent.trim();
+    a.addEventListener('click', function(e) {
+      e.preventDefault();
+      var toolbar = document.querySelector('.toolbar');
+      var offset = toolbar ? toolbar.getBoundingClientRect().height : 0;
+      var y = h.getBoundingClientRect().top + window.pageYOffset - offset - 8;
+      window.scrollTo({top: y, behavior: 'smooth'});
+      history.replaceState(null, '', '#' + h.id);
+    });
+    row.appendChild(caret);
+    row.appendChild(a);
+    li.appendChild(row);
+    parent.ul.appendChild(li);
+    linkByHeading.set(h, a);
+    liByHeading.set(h, li);
+    stack.push({ level: level, ul: null, li: li });
+  });
+
+  // Wire up carets for items that ended up with child <ul>.
+  listRoot.querySelectorAll('li').forEach(function(li) {
+    var childUl = li.querySelector(':scope > ul');
+    if (!childUl) return;
+    var caret = li.querySelector(':scope > .toc-row > .toc-caret');
+    if (!caret) return;
+    caret.classList.remove('empty');
+    caret.addEventListener('click', function(e) {
+      e.preventDefault();
+      e.stopPropagation();
+      li.classList.toggle('open');
+    });
+  });
+
+  // Initial expansion: open ancestors of items at or above initialOpenThreshold,
+  // so the first two heading levels are visible while deeper ones stay folded.
+  headings.forEach(function(h) {
+    var level = parseInt(h.tagName.substring(1), 10);
+    if (level >= initialOpenThreshold) return;
+    var li = liByHeading.get(h);
+    var node = li;
+    while (node && node.tagName === 'LI') {
+      node.classList.add('open');
+      var parentUl = node.parentElement;
+      node = parentUl ? parentUl.closest('li') : null;
+    }
+  });
+
+  // Toggle panel visibility.
+  function setVisible(v) {
+    document.body.classList.toggle('toc-visible', v);
+    try { localStorage.setItem(STORAGE_KEY, v ? '1' : '0'); } catch (e) {}
+  }
+  toggleBtn.addEventListener('click', function() {
+    setVisible(!document.body.classList.contains('toc-visible'));
+  });
+  var saved = null;
+  try { saved = localStorage.getItem(STORAGE_KEY); } catch (e) {}
+  if (saved === '1') setVisible(true);
+
+  // Scroll following: the active heading is the last one whose top is at or
+  // above a reference line just below the sticky toolbar. This mirrors the
+  // reading position regardless of scroll direction.
+  var active = null;
+  function updateActive() {
+    var toolbar = document.querySelector('.toolbar');
+    var offset = toolbar ? toolbar.getBoundingClientRect().height : 0;
+    var ref = offset + 10;
+    var candidate = null;
+    for (var i = 0; i < headings.length; i++) {
+      if (headings[i].getBoundingClientRect().top <= ref) {
+        candidate = headings[i];
+      } else {
+        break;
+      }
+    }
+    if (!candidate) candidate = headings[0];
+    if (candidate === active) return;
+    if (active) {
+      var prev = linkByHeading.get(active);
+      if (prev) prev.classList.remove('active');
+    }
+    active = candidate;
+    var link = linkByHeading.get(active);
+    if (link) {
+      link.classList.add('active');
+      var li = liByHeading.get(active);
+      var node = li ? li.parentElement : null;
+      while (node && node !== listRoot) {
+        if (node.tagName === 'LI') node.classList.add('open');
+        node = node.parentElement;
+      }
+    }
+  }
+  var ticking = false;
+  function onScroll() {
+    if (ticking) return;
+    ticking = true;
+    requestAnimationFrame(function() {
+      updateActive();
+      ticking = false;
+    });
+  }
+  window.addEventListener('scroll', onScroll, { passive: true });
+  updateActive();
+})();
+</script>`
