diff --git a/app/src/App.jsx b/app/src/App.jsx
index de593f5..755a969 100644
--- a/app/src/App.jsx
+++ b/app/src/App.jsx
@@ -208,6 +208,40 @@ function CategorySection({ title, items, defaultOpen, quarantineDir, onQuarantin
   );
 }
 
+/**
+ * Compact summary showing top categories ranked by reclaimable bytes.
+ * Gives users an immediate overview of where space is consumed
+ * before they dive into individual expandable sections.
+ */
+function TopCategoriesSummary({ items, cap = 5 }) {
+  if (!items || items.length === 0) return null;
+
+  const categories = byCategory(items)
+    .map(([cat, catItems]) => ({
+      key: cat,
+      label: CATEGORY_LABEL[cat] ?? cat,
+      total: catItems.reduce((s, f) => s + f.reclaimable, 0),
+    }))
+    .filter((c) => c.total > 0)
+    .slice(0, cap);
+
+  if (categories.length === 0) return null;
+
+  return (
+    <div className="top-categories-summary" aria-label="Top categories">
+      <h3 className="top-categories-title">Top categories</h3>
+      <ul className="top-categories-list">
+        {categories.map((c) => (
+          <li key={c.key} className="top-category-row">
+            <span className="top-category-label">{c.label}</span>
+            <span className="top-category-size">{humanBytes(c.total)}</span>
+          </li>
+        ))}
+      </ul>
+    </div>
+  );
+}
+
 function DuplicatesSection({ sets }) {
   const [isOpen, setIsOpen] = useState(true);
   if (sets.length === 0) return null;
@@ -673,6 +707,8 @@ export default function App() {
             onRestored={handleRestored}
           />
 
+          <TopCategoriesSummary items={visibleFindings} />
+
           <DuplicatesSection sets={duplicateSets} />
           <CategorySection
             title="Safe to remove"
diff --git a/app/src/App.test.mjs b/app/src/App.test.mjs
index a79e5e2..de1a1d1 100644
--- a/app/src/App.test.mjs
+++ b/app/src/App.test.mjs
@@ -125,3 +125,21 @@ test("the region is empty while idle and announces cancelling", () => {
     "pressing Cancel should announce that the scan is stopping"
   );
 });
+
+test("shows a compact top-categories summary above the detailed results", () => {
+  assert.match(jsx, /function TopCategoriesSummary/);
+  assert.match(jsx, /className="top-categories-summary"/);
+  assert.match(jsx, /<h3 className="top-categories-title">Top categories<\/h3>/);
+  assert.match(jsx, /className="top-categories-list"/);
+  assert.match(jsx, /className="top-category-row"/);
+  assert.match(jsx, /<TopCategoriesSummary items=\{visibleFindings\} \/>/);
+
+  // Verifies TopCategoriesSummary is mounted above DuplicatesSection and CategorySection
+  const summaryIdx = jsx.indexOf("<TopCategoriesSummary");
+  const duplicatesIdx = jsx.indexOf("<DuplicatesSection");
+  const categorySectionIdx = jsx.indexOf("<CategorySection");
+  assert.ok(summaryIdx > 0, "TopCategoriesSummary must be rendered in App");
+  assert.ok(summaryIdx < duplicatesIdx, "TopCategoriesSummary must render above DuplicatesSection");
+  assert.ok(summaryIdx < categorySectionIdx, "TopCategoriesSummary must render above CategorySection");
+});
+
diff --git a/app/src/styles.css b/app/src/styles.css
index 118ec7b..8f9aacc 100644
--- a/app/src/styles.css
+++ b/app/src/styles.css
@@ -39,6 +39,43 @@ button { padding: 0.6rem 1.4rem; font-size: 1rem; cursor: pointer; }
 .summary { line-height: 1.5; }
 .scanned-folder { font-family: ui-monospace, monospace; font-size: 0.85rem; opacity: 0.7; }
 
+/* Top categories compact summary */
+.top-categories-summary {
+  margin: 1rem 0 0.5rem;
+  padding: 0.75rem 1rem;
+  background: rgba(128, 128, 128, 0.06);
+  border: 1px solid rgba(128, 128, 128, 0.2);
+  border-radius: 8px;
+}
+.top-categories-title {
+  margin: 0 0 0.5rem;
+  font-size: 0.9rem;
+  font-weight: 600;
+  opacity: 0.85;
+}
+.top-categories-list {
+  list-style: none;
+  padding: 0;
+  margin: 0;
+  display: grid;
+  gap: 0.35rem;
+}
+.top-category-row {
+  display: flex;
+  justify-content: space-between;
+  align-items: baseline;
+  font-size: 0.85rem;
+}
+.top-category-label {
+  opacity: 0.85;
+}
+.top-category-size {
+  font-family: ui-monospace, monospace;
+  font-size: 0.85rem;
+  font-weight: 500;
+  opacity: 0.9;
+}
+
 /* Collapsible verdict/category groups */
 .verdict-group { margin-top: 1.25rem; }
 .group-header {
diff --git a/app/src/styles.test.mjs b/app/src/styles.test.mjs
index ab8c2a0..8bd7bc4 100644
--- a/app/src/styles.test.mjs
+++ b/app/src/styles.test.mjs
@@ -101,3 +101,11 @@ test("category badges have quiet styling", () => {
   assert.match(css, /\.category-badge\s*\{[^}]*font-size\s*:/s);
 });
 
+test("top categories summary has compact card styling", () => {
+  assert.match(css, /\.top-categories-summary\s*\{[^}]*border-radius\s*:/s);
+  assert.match(css, /\.top-categories-title\s*\{[^}]*font-weight\s*:/s);
+  assert.match(css, /\.top-category-row\s*\{[^}]*display\s*:\s*flex\b/s);
+  assert.match(css, /\.top-category-size\s*\{[^}]*font-family\s*:\s*ui-monospace/s);
+});
+
+
diff --git a/changelog.d/158-top-categories-summary.added.md b/changelog.d/158-top-categories-summary.added.md
new file mode 100644
index 0000000..22e2126
--- /dev/null
+++ b/changelog.d/158-top-categories-summary.added.md
@@ -0,0 +1,2 @@
+- Show a compact top-categories summary card above detailed scan results
+  ranking space by reclaimable bytes for both preview and final reports.