diff --git a/studio/src/components/OverviewTab.jsx b/studio/src/components/OverviewTab.jsx
index 9e17b9e..239a215 100644
--- a/studio/src/components/OverviewTab.jsx
+++ b/studio/src/components/OverviewTab.jsx
@@ -1,3 +1,4 @@
+import { useMemo } from "react";
 import {
   BarChart3,
   Hash,
@@ -8,37 +9,23 @@ import {
 } from "lucide-react";
 import { Stat, Bar, Chip, SentimentChip } from "./primitives.jsx";
 import { TONE_COLOR } from "../lib/lexicons.js";
+import { overviewStats } from "../lib/stats.js";
 
 /* ============================================================
  * OVERVIEW TAB
  * ============================================================ */
 
 export function OverviewTab({ tweets }) {
-  const total = tweets.length;
-  const byLabel = { positive: 0, neutral: 0, negative: 0 };
-  const toneCounts = {};
-  let totalLikes = 0,
-    totalRts = 0,
-    totalReplies = 0,
-    totalLen = 0,
-    totalEmoji = 0,
-    totalHashtags = 0;
-  for (const t of tweets) {
-    byLabel[t.sentiment.label]++;
-    for (const tag of t.tones) toneCounts[tag] = (toneCounts[tag] || 0) + 1;
-    totalLikes += t.likes;
-    totalRts += t.retweets;
-    totalReplies += t.replies;
-    totalLen += t.length;
-    totalEmoji += t.emoji;
-    totalHashtags += t.hashtags;
-  }
-  const toneSorted = Object.entries(toneCounts).sort((a, b) => b[1] - a[1]);
-  const avgLen = total ? Math.round(totalLen / total) : 0;
-  const avgEmoji = total ? (totalEmoji / total).toFixed(1) : 0;
-  const top = [...tweets]
-    .sort((a, b) => b.engagement - a.engagement)
-    .slice(0, 5);
+  const {
+    total,
+    byLabel,
+    toneSorted,
+    avgLen,
+    avgEmoji,
+    top,
+    totalLikes,
+    totalRts,
+  } = useMemo(() => overviewStats(tweets), [tweets]);
 
   return (
     <div className="space-y-6">
diff --git a/studio/src/lib/stats.js b/studio/src/lib/stats.js
new file mode 100644
index 0000000..984859d
--- /dev/null
+++ b/studio/src/lib/stats.js
@@ -0,0 +1,49 @@
+/* ============================================================
+ * OVERVIEW STATS
+ * ============================================================ */
+
+// Aggregate the dashboard metrics for the Overview tab. Pure and
+// framework-free so the component can memoize it and it can be unit-tested
+// directly. Logic moved verbatim out of OverviewTab.
+export function overviewStats(tweets) {
+  const total = tweets.length;
+  const byLabel = { positive: 0, neutral: 0, negative: 0 };
+  const toneCounts = {};
+  let totalLikes = 0,
+    totalRts = 0,
+    totalReplies = 0,
+    totalLen = 0,
+    totalEmoji = 0,
+    totalHashtags = 0;
+  for (const t of tweets) {
+    byLabel[t.sentiment.label]++;
+    for (const tag of t.tones) toneCounts[tag] = (toneCounts[tag] || 0) + 1;
+    totalLikes += t.likes;
+    totalRts += t.retweets;
+    totalReplies += t.replies;
+    totalLen += t.length;
+    totalEmoji += t.emoji;
+    totalHashtags += t.hashtags;
+  }
+  const toneSorted = Object.entries(toneCounts).sort((a, b) => b[1] - a[1]);
+  const avgLen = total ? Math.round(totalLen / total) : 0;
+  const avgEmoji = total ? (totalEmoji / total).toFixed(1) : 0;
+  const top = [...tweets]
+    .sort((a, b) => b.engagement - a.engagement)
+    .slice(0, 5);
+  return {
+    total,
+    byLabel,
+    toneCounts,
+    totalLikes,
+    totalRts,
+    totalReplies,
+    totalLen,
+    totalEmoji,
+    totalHashtags,
+    toneSorted,
+    avgLen,
+    avgEmoji,
+    top,
+  };
+}
diff --git a/studio/src/lib/stats.test.js b/studio/src/lib/stats.test.js
new file mode 100644
index 0000000..1752e22
--- /dev/null
+++ b/studio/src/lib/stats.test.js
@@ -0,0 +1,65 @@
+import { describe, it, expect } from "vitest";
+import { overviewStats } from "./stats.js";
+
+function tw(over) {
+  return {
+    sentiment: { label: "neutral" },
+    tones: [],
+    likes: 0,
+    retweets: 0,
+    replies: 0,
+    length: 0,
+    emoji: 0,
+    hashtags: 0,
+    engagement: 0,
+    ...over,
+  };
+}
+
+describe("overviewStats", () => {
+  it("returns zeros and empties for no tweets", () => {
+    const s = overviewStats([]);
+    expect(s.total).toBe(0);
+    expect(s.byLabel).toEqual({ positive: 0, neutral: 0, negative: 0 });
+    expect(s.avgLen).toBe(0);
+    expect(s.toneSorted).toEqual([]);
+    expect(s.top).toEqual([]);
+  });
+
+  it("counts sentiment labels", () => {
+    const s = overviewStats([
+      tw({ sentiment: { label: "positive" } }),
+      tw({ sentiment: { label: "positive" } }),
+      tw({ sentiment: { label: "negative" } }),
+    ]);
+    expect(s.total).toBe(3);
+    expect(s.byLabel).toEqual({ positive: 2, neutral: 0, negative: 1 });
+  });
+
+  it("sums engagement metrics and averages length/emoji", () => {
+    const s = overviewStats([
+      tw({ likes: 10, retweets: 2, length: 100, emoji: 2 }),
+      tw({ likes: 5, retweets: 0, length: 50, emoji: 0 }),
+    ]);
+    expect(s.totalLikes).toBe(15);
+    expect(s.totalRts).toBe(2);
+    expect(s.avgLen).toBe(75); // (100 + 50) / 2
+    expect(s.avgEmoji).toBe("1.0"); // (2 + 0) / 2, toFixed(1)
+  });
+
+  it("tallies tones sorted by frequency descending", () => {
+    const s = overviewStats([
+      tw({ tones: ["Excited", "CTA"] }),
+      tw({ tones: ["Excited"] }),
+    ]);
+    expect(s.toneSorted[0]).toEqual(["Excited", 2]);
+    expect(s.toneSorted).toContainEqual(["CTA", 1]);
+  });
+
+  it("ranks top performers by engagement and caps at 5", () => {
+    const tweets = [1, 5, 3, 2, 9, 4, 7].map((e) => tw({ engagement: e }));
+    const s = overviewStats(tweets);
+    expect(s.top).toHaveLength(5);
+    expect(s.top.map((t) => t.engagement)).toEqual([9, 7, 5, 4, 3]);
+  });
+});