diff --git a/scripts/generate-large-graph.mjs b/scripts/generate-large-graph.mjs
new file mode 100644
index 0000000..8a18360
--- /dev/null
+++ b/scripts/generate-large-graph.mjs
@@ -0,0 +1,147 @@
+#!/usr/bin/env node
+/**
+ * Generate a large fake knowledge graph for testing PR #18
+ * (Web Worker layout for large graphs).
+ *
+ * Usage:
+ *   node scripts/generate-large-graph.mjs [nodeCount]
+ *
+ * Default: 3000 nodes. Writes to .understand-anything/knowledge-graph.json
+ */
+
+import { writeFileSync, mkdirSync } from "node:fs";
+import { resolve } from "node:path";
+
+const NODE_COUNT = parseInt(process.argv[2] || "3000", 10);
+const EDGE_RATIO = 1.7; // edges per node (realistic for codebases)
+
+const nodeTypes = ["file", "function", "class", "module", "concept"];
+const edgeTypes = [
+  "imports", "exports", "contains", "inherits", "implements",
+  "calls", "subscribes", "publishes", "middleware",
+  "reads_from", "writes_to", "transforms", "validates",
+  "depends_on", "tested_by", "configures",
+  "related", "similar_to",
+];
+const complexities = ["simple", "moderate", "complex"];
+const languages = ["TypeScript", "JavaScript", "Python", "Go", "Rust"];
+const frameworks = ["React", "Express", "FastAPI", "Gin", "Actix"];
+
+function pick(arr) {
+  return arr[Math.floor(Math.random() * arr.length)];
+}
+
+function generateNodes(count) {
+  const nodes = [];
+  for (let i = 0; i < count; i++) {
+    const type = pick(nodeTypes);
+    const name = `${type}_${i}`;
+    nodes.push({
+      id: `node-${i}`,
+      type,
+      name,
+      filePath: type === "file" ? `src/${name}.ts` : undefined,
+      summary: `Auto-generated ${type} node #${i} for performance testing.`,
+      tags: [type, `group-${i % 20}`],
+      complexity: pick(complexities),
+    });
+  }
+  return nodes;
+}
+
+function generateEdges(nodes, edgeCount) {
+  const edges = [];
+  const seen = new Set();
+  const n = nodes.length;
+
+  for (let i = 0; i < edgeCount; i++) {
+    let src, tgt;
+    // Forward-only edges to avoid cycles (dagre blows the stack on large cyclic graphs)
+    do {
+      src = Math.floor(Math.random() * (n - 1));
+      const offset = Math.floor(Math.random() * Math.min(50, n - src - 1)) + 1;
+      tgt = src + offset;
+    } while (tgt >= n || src === tgt || seen.has(`${src}-${tgt}`));
+
+    seen.add(`${src}-${tgt}`);
+    edges.push({
+      source: nodes[src].id,
+      target: nodes[tgt].id,
+      type: pick(edgeTypes),
+      direction: "forward",
+      weight: Math.round(Math.random() * 100) / 100,
+    });
+  }
+  return edges;
+}
+
+function generateLayers(nodes) {
+  const layers = [];
+  const layerNames = [
+    "Presentation", "Application", "Domain", "Infrastructure",
+    "API Gateway", "Data Access", "Utilities", "Testing",
+  ];
+
+  for (let i = 0; i < layerNames.length; i++) {
+    const start = Math.floor((i / layerNames.length) * nodes.length);
+    const end = Math.floor(((i + 1) / layerNames.length) * nodes.length);
+    layers.push({
+      id: `layer-${i}`,
+      name: layerNames[i],
+      description: `${layerNames[i]} layer (auto-generated)`,
+      nodeIds: nodes.slice(start, end).map((n) => n.id),
+    });
+  }
+  return layers;
+}
+
+function generateTour(nodes) {
+  const steps = [];
+  const stepCount = Math.min(8, Math.floor(nodes.length / 100));
+  for (let i = 0; i < stepCount; i++) {
+    const idx = Math.floor((i / stepCount) * nodes.length);
+    steps.push({
+      order: i + 1,
+      title: `Step ${i + 1}: Explore ${nodes[idx].name}`,
+      description: `This tour step highlights node **${nodes[idx].name}** and its surrounding context.`,
+      nodeIds: [nodes[idx].id, nodes[Math.min(idx + 1, nodes.length - 1)].id],
+    });
+  }
+  return steps;
+}
+
+// ── Generate ──
+
+const nodes = generateNodes(NODE_COUNT);
+const edgeCount = Math.floor(NODE_COUNT * EDGE_RATIO);
+const edges = generateEdges(nodes, edgeCount);
+const layers = generateLayers(nodes);
+const tour = generateTour(nodes);
+
+const graph = {
+  version: "1.0",
+  project: {
+    name: "large-test-project",
+    languages: languages.slice(0, 3),
+    frameworks: frameworks.slice(0, 2),
+    description: `Auto-generated project with ${NODE_COUNT} nodes for performance testing.`,
+    analyzedAt: new Date().toISOString(),
+    gitCommitHash: "0000000000000000000000000000000000000000",
+  },
+  nodes,
+  edges,
+  layers,
+  tour,
+};
+
+const outDir = resolve(process.cwd(), ".understand-anything");
+mkdirSync(outDir, { recursive: true });
+const outPath = resolve(outDir, "knowledge-graph.json");
+writeFileSync(outPath, JSON.stringify(graph, null, 2));
+
+console.log(`Generated knowledge graph:`);
+console.log(`  Nodes: ${nodes.length}`);
+console.log(`  Edges: ${edges.length}`);
+console.log(`  Layers: ${layers.length}`);
+console.log(`  Tour steps: ${tour.length}`);
+console.log(`  Written to: ${outPath}`);