diff --git a/src/components/NotFoundPage.test.tsx b/src/components/NotFoundPage.test.tsx
new file mode 100644
index 000000000..23869764b
--- /dev/null
+++ b/src/components/NotFoundPage.test.tsx
@@ -0,0 +1,26 @@
+/* @vitest-environment jsdom */
+
+import { render, screen } from "@testing-library/react";
+import type { ReactNode } from "react";
+import { describe, expect, it, vi } from "vitest";
+import { NotFoundPage } from "./NotFoundPage";
+
+vi.mock("@tanstack/react-router", () => ({
+  Link: ({ children, to, className }: { children: ReactNode; to: string; className?: string }) => (
+    <a href={to} className={className}>
+      {children}
+    </a>
+  ),
+}));
+
+describe("NotFoundPage", () => {
+  it("renders a single recovery action back to the homepage", () => {
+    render(<NotFoundPage />);
+
+    expect(screen.getByText("404 • Page not found")).toBeTruthy();
+    expect(screen.getByRole("link", { name: "Return home" }).getAttribute("href")).toBe("/");
+    expect(screen.queryByText("Lost route")).toBeNull();
+    expect(screen.queryByText("Try next")).toBeNull();
+    expect(screen.queryByRole("link", { name: /Browse / })).toBeNull();
+  });
+});
diff --git a/src/components/NotFoundPage.tsx b/src/components/NotFoundPage.tsx
new file mode 100644
index 000000000..b4ef879a0
--- /dev/null
+++ b/src/components/NotFoundPage.tsx
@@ -0,0 +1,23 @@
+import { Link } from "@tanstack/react-router";
+
+export function NotFoundPage() {
+  return (
+    <main className="section not-found-page">
+      <section className="card not-found-card">
+        <span className="not-found-eyebrow">404 • Page not found</span>
+        <div className="not-found-copy">
+          <h1 className="section-title not-found-title">This page drifted out of reach.</h1>
+          <p className="section-subtitle not-found-description">
+            The link may be outdated, the URL may have a typo, or this page may have moved.
+            Let&apos;s get you back to something useful.
+          </p>
+          <div className="not-found-actions">
+            <Link to="/" className="btn btn-primary">
+              Return home
+            </Link>
+          </div>
+        </div>
+      </section>
+    </main>
+  );
+}
diff --git a/src/router.test.tsx b/src/router.test.tsx
new file mode 100644
index 000000000..60c06bec3
--- /dev/null
+++ b/src/router.test.tsx
@@ -0,0 +1,17 @@
+import { beforeAll, describe, expect, it } from "vitest";
+import { NotFoundPage } from "./components/NotFoundPage";
+
+describe("getRouter", () => {
+  beforeAll(() => {
+    process.env.VITE_CONVEX_URL = "https://example.convex.cloud";
+    process.env.VITE_CONVEX_SITE_URL = "https://example.convex.site";
+    process.env.SITE_URL = "http://localhost:3000";
+  });
+
+  it("registers the shared not found component", async () => {
+    const { getRouter } = await import("./router");
+    const router = getRouter();
+
+    expect(router.options.defaultNotFoundComponent).toBe(NotFoundPage);
+  });
+});
diff --git a/src/router.tsx b/src/router.tsx
index 1059a00ca..e8840fb0d 100644
--- a/src/router.tsx
+++ b/src/router.tsx
@@ -1,4 +1,5 @@
 import { createRouter } from "@tanstack/react-router";
+import { NotFoundPage } from "./components/NotFoundPage";
 // Import the generated route tree
 import { routeTree } from "./routeTree.gen";
 
@@ -10,6 +11,7 @@ export const getRouter = () => {
 
     scrollRestoration: true,
     defaultPreloadStaleTime: 0,
+    defaultNotFoundComponent: NotFoundPage,
   });
 
   return router;
diff --git a/src/styles.css b/src/styles.css
index 0c2d9875c..fb311f7c3 100644
--- a/src/styles.css
+++ b/src/styles.css
@@ -436,6 +436,76 @@ code {
   box-sizing: border-box;
 }
 
+.not-found-page {
+  display: flex;
+  align-items: center;
+  min-height: clamp(420px, 62vh, 640px);
+}
+
+.not-found-card {
+  position: relative;
+  overflow: hidden;
+  gap: 20px;
+  padding: clamp(28px, 4vw, 42px);
+  background:
+    radial-gradient(circle at top right, rgba(255, 118, 84, 0.16), transparent 36%),
+    radial-gradient(circle at bottom left, rgba(32, 158, 146, 0.12), transparent 38%),
+    linear-gradient(180deg, color-mix(in srgb, var(--surface) 96%, white 4%), var(--surface));
+  box-shadow: var(--shadow);
+}
+
+.not-found-eyebrow {
+  display: inline-flex;
+  width: fit-content;
+  align-items: center;
+  gap: 8px;
+  padding: 6px 12px;
+  border-radius: 999px;
+  border: 1px solid rgba(255, 118, 84, 0.24);
+  background: rgba(255, 118, 84, 0.1);
+  color: var(--accent-deep);
+  font-size: 0.78rem;
+  font-weight: 700;
+  letter-spacing: 0.08em;
+  text-transform: uppercase;
+}
+
+.not-found-copy {
+  display: grid;
+  gap: 14px;
+  max-width: 58ch;
+}
+
+.not-found-title {
+  margin: 0;
+  max-width: 12ch;
+  font-size: clamp(2.4rem, 5vw, 3.6rem);
+  line-height: 0.95;
+}
+
+.not-found-description {
+  margin: 0;
+  font-size: 1rem;
+  line-height: 1.7;
+}
+
+.not-found-actions {
+  display: flex;
+  flex-wrap: wrap;
+  gap: 12px;
+}
+
+@media (max-width: 760px) {
+  .not-found-title {
+    max-width: none;
+  }
+
+  .not-found-actions .btn {
+    width: 100%;
+    justify-content: center;
+  }
+}
+
 .upload-shell {
   position: relative;
 }