diff --git a/frontend/app.js b/frontend/app.js
index 4f4b54b..cdc6517 100644
--- a/frontend/app.js
+++ b/frontend/app.js
@@ -4,6 +4,8 @@ const SCHEMA_URL = "/schemeta.schema.json";
 const NET_CLASSES = ["power", "ground", "signal", "analog", "differential", "clock", "bus"];
 const PIN_SIDES = ["left", "right", "top", "bottom"];
 const PIN_TYPES = ["power_in", "power_out", "input", "output", "bidirectional", "passive", "analog", "ground"];
+const LIST_ROW_HEIGHT = 36;
+const LIST_OVERSCAN_ROWS = 8;
 
 const state = {
   model: null,
@@ -721,6 +723,26 @@ function resolveLabelCollisions(svg) {
   }
 }
 
+function renderVirtualList(listEl, allItems, renderRow, rowHeight = LIST_ROW_HEIGHT) {
+  const items = Array.isArray(allItems) ? allItems : [];
+  if (!items.length) {
+    listEl.innerHTML = "";
+    return;
+  }
+
+  const viewportHeight = Math.max(rowHeight * 4, listEl.clientHeight || 230);
+  const scrollTop = listEl.scrollTop;
+  const total = items.length;
+  const visibleRows = Math.ceil(viewportHeight / rowHeight);
+  const start = Math.max(0, Math.floor(scrollTop / rowHeight) - LIST_OVERSCAN_ROWS);
+  const end = Math.min(total, start + visibleRows + LIST_OVERSCAN_ROWS * 2);
+  const topPad = start * rowHeight;
+  const bottomPad = (total - end) * rowHeight;
+
+  const rows = items.slice(start, end).map(renderRow).join("");
+  listEl.innerHTML = `<li class="listSpacer" style="height:${topPad}px"></li>${rows}<li class="listSpacer" style="height:${bottomPad}px"></li>`;
+}
+
 function renderInstances() {
   if (!state.model) {
     el.instanceList.innerHTML = "";
@@ -730,12 +752,15 @@ function renderInstances() {
   const q = el.instanceFilter.value.trim().toLowerCase();
   const items = state.model.instances.filter((i) => i.ref.toLowerCase().includes(q));
 
-  el.instanceList.innerHTML = items
-    .map((inst) => {
+  renderVirtualList(
+    el.instanceList,
+    items,
+    (inst) => {
       const cls = state.selectedRefs.includes(inst.ref) ? "active" : "";
       return `<li class="${cls}" data-ref-item="${inst.ref}">${inst.ref} · ${inst.symbol}</li>`;
-    })
-    .join("");
+    },
+    LIST_ROW_HEIGHT
+  );
 }
 
 function renderNets() {
@@ -747,12 +772,15 @@ function renderNets() {
   const q = el.netFilter.value.trim().toLowerCase();
   const items = state.model.nets.filter((n) => n.name.toLowerCase().includes(q));
 
-  el.netList.innerHTML = items
-    .map((net) => {
+  renderVirtualList(
+    el.netList,
+    items,
+    (net) => {
       const cls = net.name === state.selectedNet ? "active" : "";
       return `<li class="${cls}" data-net-item="${net.name}">${net.name} <small>(${net.class})</small></li>`;
-    })
-    .join("");
+    },
+    LIST_ROW_HEIGHT
+  );
 }
 
 function netByName(name) {
@@ -1843,8 +1871,16 @@ async function loadSample() {
 }
 
 function setupEvents() {
-  el.instanceFilter.addEventListener("input", renderInstances);
-  el.netFilter.addEventListener("input", renderNets);
+  el.instanceFilter.addEventListener("input", () => {
+    el.instanceList.scrollTop = 0;
+    renderInstances();
+  });
+  el.netFilter.addEventListener("input", () => {
+    el.netList.scrollTop = 0;
+    renderNets();
+  });
+  el.instanceList.addEventListener("scroll", renderInstances, { passive: true });
+  el.netList.addEventListener("scroll", renderNets, { passive: true });
 
   el.instanceList.addEventListener("click", (evt) => {
     const item = evt.target.closest("[data-ref-item]");
diff --git a/frontend/styles.css b/frontend/styles.css
index a451a19..ba84fe5 100644
--- a/frontend/styles.css
+++ b/frontend/styles.css
@@ -182,6 +182,13 @@ textarea {
   background: var(--accent-soft);
 }
 
+.list li.listSpacer {
+  padding: 0;
+  border: none;
+  cursor: default;
+  background: transparent;
+}
+
 .card {
   border: 1px solid var(--line);
   border-radius: 8px;