diff --git a/web/src/app/_ui/section-header.tsx b/web/src/app/_ui/section-header.tsx
index ef14af5..0c1a528 100644
--- a/web/src/app/_ui/section-header.tsx
+++ b/web/src/app/_ui/section-header.tsx
@@ -1,4 +1,6 @@
-export function SectionHeader({ title, note }: { title: string; note?: string }) {
+import type { ReactNode } from "react";
+
+export function SectionHeader({ title, note }: { title: string; note?: ReactNode }) {
   return (
     <div className="dept">
       <h2>{title}</h2>
diff --git a/web/src/app/api/library/integrity/route.test.ts b/web/src/app/api/library/integrity/route.test.ts
new file mode 100644
index 0000000..9efe3f7
--- /dev/null
+++ b/web/src/app/api/library/integrity/route.test.ts
@@ -0,0 +1,63 @@
+import { describe, it, expect, beforeEach, afterEach } from "vitest";
+import { mkdtempSync, mkdirSync, writeFileSync, rmSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { prisma } from "@/lib/db";
+import { GET } from "./route";
+
+let root: string;
+const original = process.env.LYRA_LIBRARY_ROOT;
+
+beforeEach(() => {
+  root = mkdtempSync(join(tmpdir(), "lyra-integ-"));
+  process.env.LYRA_LIBRARY_ROOT = root;
+});
+afterEach(() => {
+  if (original === undefined) delete process.env.LYRA_LIBRARY_ROOT;
+  else process.env.LYRA_LIBRARY_ROOT = original;
+  rmSync(root, { recursive: true, force: true });
+});
+
+async function item(artist: string, album: string, dir: string, trackNames: string[] = []) {
+  return prisma.libraryItem.create({
+    data: { artist, album, path: dir, source: "scan", format: "FLAC", qualityClass: 2, trackNames },
+  });
+}
+
+describe("library integrity API", () => {
+  it("flags a healthy album with no issues", async () => {
+    const dir = join(root, "A", "Good (2020)");
+    mkdirSync(dir, { recursive: true });
+    writeFileSync(join(dir, "01 One.flac"), "xxxx");
+    writeFileSync(join(dir, "02 Two.flac"), "yyyy");
+    await item("A", "Good", dir, ["01 One.flac", "02 Two.flac"]);
+    const { checked, issues } = await (await GET()).json();
+    expect(checked).toBe(1);
+    expect(issues).toEqual([]);
+  });
+
+  it("flags a missing folder, empty files, and a track-count drift", async () => {
+    await item("Gone", "Missing", join(root, "Gone", "Missing"));
+
+    const zdir = join(root, "Z", "Zero (2021)");
+    mkdirSync(zdir, { recursive: true });
+    writeFileSync(join(zdir, "01 A.flac"), ""); // 0 bytes → truncated
+    writeFileSync(join(zdir, "02 B.flac"), "ok");
+    await item("Z", "Zero", zdir, ["01 A.flac", "02 B.flac", "03 C.flac"]); // expected 3, on disk 2
+
+    const { issues } = await (await GET()).json();
+    const byAlbum = Object.fromEntries(issues.map((i: { album: string; issues: string[] }) => [i.album, i.issues]));
+    expect(byAlbum["Missing"]).toEqual(["folder is missing on disk"]);
+    expect(byAlbum["Zero"]).toContain("1 empty/unreadable file");
+    expect(byAlbum["Zero"]).toContain("2 of 3 tracks on disk");
+  });
+
+  it("flags a folder with no audio", async () => {
+    const dir = join(root, "N", "NoAudio");
+    mkdirSync(dir, { recursive: true });
+    writeFileSync(join(dir, "cover.jpg"), "img");
+    await item("N", "NoAudio", dir);
+    const { issues } = await (await GET()).json();
+    expect(issues[0].issues).toEqual(["no audio files in the folder"]);
+  });
+});
diff --git a/web/src/app/api/library/integrity/route.ts b/web/src/app/api/library/integrity/route.ts
new file mode 100644
index 0000000..8ce3c6b
--- /dev/null
+++ b/web/src/app/api/library/integrity/route.ts
@@ -0,0 +1,51 @@
+import { readdir, stat } from "node:fs/promises";
+import { join, resolve, sep, extname } from "node:path";
+import { prisma } from "@/lib/db";
+
+// GET /api/library/integrity — on-demand disk check of every owned album folder (via the
+// /music mount). Flags folders that are missing, hold no audio, contain zero-byte (truncated)
+// files, or whose on-disk audio count drifted from what was captured at import/scan. Cheap
+// (metadata only: readdir + stat), so it runs only when the user asks.
+const AUDIO_EXT = new Set([".flac", ".mp3", ".m4a", ".opus", ".ogg", ".aac", ".wav"]);
+
+export async function GET() {
+  const items = await prisma.libraryItem.findMany({ orderBy: [{ artist: "asc" }, { album: "asc" }] });
+  const root = resolve(process.env.LYRA_LIBRARY_ROOT ?? "/music");
+
+  const results = await Promise.all(
+    items.map(async (li) => {
+      const dir = resolve(li.path);
+      const issues: string[] = [];
+      if (dir !== root && !dir.startsWith(root + sep)) {
+        return { id: li.id, artist: li.artist, album: li.album, issues: ["path is outside the library root"] };
+      }
+      let names: string[];
+      try {
+        names = await readdir(dir);
+      } catch {
+        return { id: li.id, artist: li.artist, album: li.album, issues: ["folder is missing on disk"] };
+      }
+      const audio = names.filter((n) => AUDIO_EXT.has(extname(n).toLowerCase()));
+      if (audio.length === 0) {
+        issues.push("no audio files in the folder");
+      } else {
+        let empty = 0;
+        for (const n of audio) {
+          try {
+            if ((await stat(join(dir, n))).size === 0) empty++;
+          } catch {
+            empty++; // unreadable counts as broken
+          }
+        }
+        if (empty > 0) issues.push(`${empty} empty/unreadable file${empty === 1 ? "" : "s"}`);
+        const expected = li.trackNames.length;
+        if (expected > 0 && audio.length !== expected) {
+          issues.push(`${audio.length} of ${expected} tracks on disk`);
+        }
+      }
+      return { id: li.id, artist: li.artist, album: li.album, issues };
+    }),
+  );
+
+  return Response.json({ checked: items.length, issues: results.filter((r) => r.issues.length > 0) });
+}
diff --git a/web/src/app/library/library-client.tsx b/web/src/app/library/library-client.tsx
index e868634..5e93ad9 100644
--- a/web/src/app/library/library-client.tsx
+++ b/web/src/app/library/library-client.tsx
@@ -33,11 +33,14 @@ const SORTS: { key: SortKey; label: string; cmp: (a: Album, b: Album) => number
 
 type Unmatched = { id: string; artist: string; album: string; path: string; reason: string };
 type DupItem = { id: string; artist: string; album: string; format: string; qualityClass: number; year: string | null };
+type IntegrityIssue = { id: string; artist: string; album: string; issues: string[] };
 
 export function LibraryClient() {
   const [albums, setAlbums] = useState<Album[]>([]);
   const [unmatched, setUnmatched] = useState<Unmatched[]>([]);
   const [duplicates, setDuplicates] = useState<DupItem[][]>([]);
+  const [integrity, setIntegrity] = useState<{ checked: number; issues: IntegrityIssue[] } | null>(null);
+  const [checking, setChecking] = useState(false);
   const [q, setQ] = useState("");
   const [sort, setSort] = useState<SortKey>("added");
   const [open, setOpen] = useState<Album | null>(null);
@@ -112,6 +115,20 @@ export function LibraryClient() {
     refresh();
   }, []);
 
+  async function checkIntegrity() {
+    setChecking(true);
+    try {
+      const res = await fetch("/api/library/integrity").catch(() => null);
+      if (res?.ok) {
+        setIntegrity(await res.json());
+      } else {
+        toast("Couldn't run the integrity check");
+      }
+    } finally {
+      setChecking(false);
+    }
+  }
+
   async function dismissUnmatched(u: Unmatched) {
     const res = await fetch(`/api/library/unmatched?id=${u.id}`, { method: "DELETE" }).catch(() => null);
     if (res?.ok) {
@@ -175,6 +192,51 @@ export function LibraryClient() {
         </div>
       ) : null}
 
+      {albums.length > 0 ? (
+        <>
+          <SectionHeader
+            title="Integrity"
+            note={
+              <button className="btn sm ghost" onClick={checkIntegrity} disabled={checking}>
+                {checking ? "Checking…" : "Check now"}
+              </button>
+            }
+          />
+          {integrity ? (
+            integrity.issues.length === 0 ? (
+              <p className="muted-note">Checked {integrity.checked} albums — no problems found.</p>
+            ) : (
+              <ul className="list">
+                {integrity.issues.map((it) => {
+                  const album = albums.find((a) => a.id === it.id);
+                  return (
+                    <li key={it.id} className="list-row">
+                      <div className="main">
+                        {album ? (
+                          <button className="linkish rtitle" onClick={() => show(album)}>
+                            {it.artist} — {it.album}
+                          </button>
+                        ) : (
+                          <div className="rtitle">{it.artist} — {it.album}</div>
+                        )}
+                        <div className="rmeta">
+                          <span className="score">{it.issues.join(" · ")}</span>
+                        </div>
+                      </div>
+                    </li>
+                  );
+                })}
+              </ul>
+            )
+          ) : (
+            <p className="muted-note">
+              Check every album folder on disk for missing folders, empty/truncated files, and
+              track-count drift.
+            </p>
+          )}
+        </>
+      ) : null}
+
       {duplicates.length > 0 ? (
         <>
           <SectionHeader title="Possible duplicates" note={`${duplicates.length}`} />