diff --git a/spike_visualizer/js/app.js b/spike_visualizer/js/app.js
new file mode 100644
index 0000000..02b5fb4
--- /dev/null
+++ b/spike_visualizer/js/app.js
@@ -0,0 +1,133 @@
+'use strict';
+
+async function initApp() {
+  const summaryContainer = document.getElementById('summary');
+  const chartContainer = document.getElementById('chart');
+  const filterPanel = document.getElementById('filter-panel');
+
+  if (!summaryContainer || !chartContainer || !filterPanel) {
+    console.error('Required DOM elements missing.');
+    return;
+  }
+
+  try {
+    const dataset = await fetchSpikeData();
+    renderSummary(dataset, summaryContainer);
+    renderChart(dataset, chartContainer);
+    bindUIEvents(dataset);
+  } catch (err) {
+    console.error('Failed to initialize app:', err);
+  }
+}
+
+async function fetchSpikeData(params = {}) {
+  const query = new URLSearchParams(params).toString();
+  const response = await fetch('/api/spikes' + (query ? '?' + query : ''));
+  if (!response.ok) {
+    throw new Error('API request failed with status ' + response.status);
+  }
+  return response.json();
+}
+
+function renderSummary(data, container) {
+  if (!Array.isArray(data)) return;
+  const total = data.length;
+  const avgReorder = total ? (data.reduce((sum, d) => sum + (d.reorder_score || 0), 0) / total).toFixed(2) : 0;
+  const avgPublish = total ? (data.reduce((sum, d) => sum + (d.publish_rate || 0), 0) / total).toFixed(2) : 0;
+
+  container.innerHTML = `
+    <div class="summary-item">Total Spikes: ${total}</div>
+    <div class="summary-item">Average Reorder Score: ${avgReorder}</div>
+    <div class="summary-item">Average Publish Rate: ${avgPublish}</div>
+  `;
+}
+
+function renderChart(data, container) {
+  if (typeof d3 === 'undefined') {
+    container.textContent = 'Visualization library (d3.js) not loaded.';
+    return;
+  }
+  container.innerHTML = '';
+  const width = container.clientWidth || 800;
+  const height = 300;
+
+  const svg = d3.select(container)
+    .append('svg')
+    .attr('width', width)
+    .attr('height', height);
+
+  const xScale = d3.scaleLinear()
+    .domain(d3.extent(data, d => d.timestamp))
+    .range([40, width - 20]);
+
+  const yScale = d3.scaleLinear()
+    .domain([0, d3.max(data, d => d.reorder_score || 0)])
+    .range([height - 40, 20]);
+
+  svg.selectAll('circle')
+    .data(data)
+    .enter()
+    .append('circle')
+    .attr('cx', d => xScale(d.timestamp))
+    .attr('cy', d => yScale(d.reorder_score))
+    .attr('r', 4)
+    .attr('fill', d => d.migration_flag ? '#d95f02' : '#1b9e77')
+    .on('mouseover', (event, d) => {
+      showTooltip(event, d, container);
+    })
+    .on('mouseout', () => {
+      hideTooltip(container);
+    });
+}
+
+function showTooltip(event, data, container) {
+  let tooltip = container.querySelector('.tooltip');
+  if (!tooltip) {
+    tooltip = document.createElement('div');
+    tooltip.className = 'tooltip';
+    container.appendChild(tooltip);
+  }
+  tooltip.innerHTML = `CPU ${data.cpu_id}<br>Score: ${data.reorder_score}<br>Rate: ${data.publish_rate}<br>Migration: ${data.migration_flag}`;
+  tooltip.style.visibility = 'visible';
+  tooltip.style.left = `${event.offsetX + 10}px`;
+  tooltip.style.top = `${event.offsetY - 20}px`;
+}
+
+function hideTooltip(container) {
+  const tooltip = container.querySelector('.tooltip');
+  if (tooltip) {
+    tooltip.style.visibility = 'hidden';
+  }
+}
+
+function bindUIEvents(initialData) {
+  const cpuFilter = document.getElementById('cpu-filter');
+  const reorderFilter = document.getElementById('reorder-filter');
+  const timeFilterStart = document.getElementById('start-time');
+  const timeFilterEnd = document.getElementById('end-time');
+  const chartContainer = document.getElementById('chart');
+  const summaryContainer = document.getElementById('summary');
+
+  if (!cpuFilter || !chartContainer) return;
+
+  const updateChart = async () => {
+    const params = {};
+    if (cpuFilter.value) params.cpu_id = cpuFilter.value;
+    if (timeFilterStart.value) params.start_time = timeFilterStart.value;
+    if (timeFilterEnd.value) params.end_time = timeFilterEnd.value;
+
+    try {
+      const newData = await fetchSpikeData(params);
+      renderSummary(newData, summaryContainer);
+      renderChart(newData, chartContainer);
+    } catch (err) {
+      console.error('Failed to update chart:', err);
+    }
+  };
+
+  [cpuFilter, reorderFilter, timeFilterStart, timeFilterEnd].forEach(el => {
+    if (el) el.addEventListener('change', updateChart);
+  });
+}
+
+window.addEventListener('load', initApp);
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