diff --git a/spike_visualizer/js/visualization.js b/spike_visualizer/js/visualization.js
new file mode 100644
index 0000000..ecf28d2
--- /dev/null
+++ b/spike_visualizer/js/visualization.js
@@ -0,0 +1,128 @@
+'use strict';
+
+(function(global){
+  const Visualization = {};
+
+  // Internal helpers
+  function clearSVG(svg){
+    if(!svg) return;
+    svg.selectAll('*').remove();
+  }
+
+  function createScales(data, width, height, xField, yField){
+    const xExtent = d3.extent(data, d => d[xField]);
+    const yExtent = d3.extent(data, d => d[yField]);
+
+    return {
+      x: d3.scaleTime().domain(xExtent).range([50, width - 20]),
+      y: d3.scaleLinear().domain(yExtent).range([height - 40, 20])
+    };
+  }
+
+  // --- renderTimeline ---
+  Visualization.renderTimeline = function(spikeData, svgContainer){
+    if(!svgContainer || !Array.isArray(spikeData)) return;
+    clearSVG(svgContainer);
+
+    const width = +svgContainer.attr('width') || 800;
+    const height = +svgContainer.attr('height') || 400;
+
+    const grouped = d3.group(spikeData, d => d.cpu_id);
+    const cpus = Array.from(grouped.keys());
+    const timeExtent = d3.extent(spikeData, d => d.timestamp);
+
+    const xScale = d3.scaleTime().domain(timeExtent).range([80, width - 40]);
+    const yScale = d3.scaleBand().domain(cpus).range([40, height - 40]).padding(0.3);
+
+    const colorScale = d3.scaleSequential(d3.interpolateRdYlBu)
+      .domain(d3.extent(spikeData, d => d.reorder_score));
+
+    // Axes
+    svgContainer.append('g')
+      .attr('transform', `translate(0,${height - 40})`)
+      .call(d3.axisBottom(xScale).ticks(6));
+
+    svgContainer.append('g')
+      .attr('transform', 'translate(80,0)')
+      .call(d3.axisLeft(yScale));
+
+    const tooltip = d3.select('body').append('div')
+      .attr('class', 'tooltip')
+      .style('opacity', 0)
+      .style('position', 'absolute')
+      .style('pointer-events', 'none');
+
+    svgContainer.selectAll('.spike-dot')
+      .data(spikeData)
+      .enter()
+      .append('circle')
+      .attr('class', 'spike-dot')
+      .attr('cx', d => xScale(d.timestamp))
+      .attr('cy', d => yScale(d.cpu_id) + yScale.bandwidth() / 2)
+      .attr('r', 4)
+      .attr('fill', d => colorScale(d.reorder_score))
+      .attr('stroke', d => d.migration_flag ? '#444' : 'none')
+      .on('mouseover', function(event, d){
+        tooltip.transition().duration(200).style('opacity', 0.95);
+        tooltip.html(`CPU: ${d.cpu_id}<br>Reorder: ${d.reorder_score}<br>Publish: ${d.publish_rate}`)
+          .style('left', (event.pageX + 5) + 'px')
+          .style('top', (event.pageY - 28) + 'px');
+      })
+      .on('mouseout', function(){
+        tooltip.transition().duration(300).style('opacity', 0);
+      });
+  };
+
+  // --- renderScatter ---
+  Visualization.renderScatter = function(spikeData, filterState){
+    const container = d3.select('#chart-container');
+    if(container.empty() || !Array.isArray(spikeData)) return;
+
+    container.selectAll('*').remove();
+    const width = 800;
+    const height = 400;
+
+    const svg = container.append('svg').attr('width', width).attr('height', height);
+    const scales = createScales(spikeData, width, height, 'timestamp', 'reorder_score');
+
+    svg.append('g')
+      .attr('transform', `translate(0,${height - 40})`)
+      .call(d3.axisBottom(scales.x).ticks(6));
+
+    svg.append('g')
+      .attr('transform', 'translate(50,0)')
+      .call(d3.axisLeft(scales.y));
+
+    const filtered = spikeData.filter(d => {
+      let include = true;
+      if(filterState && filterState.cpu_id) include = include && d.cpu_id === filterState.cpu_id;
+      if(filterState && filterState.min_score != null) include = include && d.reorder_score >= filterState.min_score;
+      if(filterState && filterState.max_score != null) include = include && d.reorder_score <= filterState.max_score;
+      return include;
+    });
+
+    svg.selectAll('.scatter-dot')
+      .data(filtered)
+      .enter()
+      .append('circle')
+      .attr('class', 'scatter-dot')
+      .attr('cx', d => scales.x(d.timestamp))
+      .attr('cy', d => scales.y(d.reorder_score))
+      .attr('r', 4)
+      .attr('fill', '#4287f5')
+      .attr('opacity', 0.75);
+  };
+
+  // --- updateView ---
+  Visualization.updateView = function(filters, newData){
+    const svg = d3.select('#timeline');
+    if(filters && filters.mode === 'scatter') {
+      Visualization.renderScatter(newData, filters);
+    } else {
+      Visualization.renderTimeline(newData, svg);
+    }
+  };
+
+  global.Visualization = Visualization;
+
+})(window);
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