diff --git a/db.py b/db.py
index f65a4de..6ba7cd1 100644
--- a/db.py
+++ b/db.py
@@ -204,5 +204,14 @@ def get_stats() -> dict:
     }
 
 
+def clear_sync_data() -> dict:
+    """Delete all processed_zips, uploaded_books, and sync_runs rows. Settings are kept."""
+    with get_db() as conn:
+        zips = conn.execute("DELETE FROM processed_zips").rowcount
+        books = conn.execute("DELETE FROM uploaded_books").rowcount
+        runs = conn.execute("DELETE FROM sync_runs").rowcount
+    return {"zips": zips, "books": books, "runs": runs}
+
+
 def _now() -> str:
     return datetime.now(timezone.utc).isoformat()
diff --git a/main.py b/main.py
index a8677dc..30605e2 100644
--- a/main.py
+++ b/main.py
@@ -174,6 +174,15 @@ async def test_calibre():
     return {"ok": ok, "message": message}
 
 
+# --- Data reset ---
+
+@app.post("/settings/reset-sync-data")
+async def reset_sync_data():
+    counts = db.clear_sync_data()
+    log.info("Sync data cleared: %s", counts)
+    return RedirectResponse("/settings?reset=1", status_code=303)
+
+
 # --- JSON status API ---
 
 @app.get("/api/status")
diff --git a/static/style.css b/static/style.css
index 809821a..efba279 100644
--- a/static/style.css
+++ b/static/style.css
@@ -153,6 +153,9 @@ tr:hover td { background: rgba(255,255,255,0.02); }
 .btn-secondary { background: transparent; color: var(--accent); border: 1px solid var(--accent); }
 .btn-secondary:hover { background: rgba(99,102,241,0.1); }
 .btn-disabled { background: var(--border); color: var(--muted); cursor: not-allowed; }
+.btn-danger { background: #dc2626; color: #fff; border: 1px solid #dc2626; }
+.btn-danger:hover { background: #b91c1c; border-color: #b91c1c; }
+.danger-zone { border-color: rgba(220,38,38,0.4); }
 
 /* Forms */
 .form-section {
diff --git a/templates/settings.html b/templates/settings.html
index d69b51e..8f29c94 100644
--- a/templates/settings.html
+++ b/templates/settings.html
@@ -148,6 +148,17 @@
   </div>
 </form>
 
+<section class="form-section danger-zone">
+  <h2>Danger zone</h2>
+  {% if request.query_params.get("reset") %}
+    <div class="alert alert-success">Sync data cleared — all processed zip and book records have been deleted.</div>
+  {% endif %}
+  <p class="muted small">Deletes all records of processed zips, uploaded books, and sync run history. Your settings are kept. Use this to start fresh after test runs.</p>
+  <form method="post" action="/settings/reset-sync-data" onsubmit="return confirm('Delete all sync data? This cannot be undone.')">
+    <button type="submit" class="btn btn-danger">Delete all sync data</button>
+  </form>
+</section>
+
 <script>
 function toggleAuth(method) {
   document.getElementById("row-key").style.display = method === "key" ? "" : "none";