diff --git a/.changeset/spicy-coins-switch.md b/.changeset/spicy-coins-switch.md
new file mode 100644
index 0000000000..744d9d9640
--- /dev/null
+++ b/.changeset/spicy-coins-switch.md
@@ -0,0 +1,5 @@
+---
+'@backstage/plugin-catalog-backend': patch
+---
+
+Fixed O(n²) performance bottleneck in `buildEntitySearch` `traverse()` by replacing `Array.some()` linear scan with a `Set` for O(1) duplicate path key detection.
diff --git a/plugins/catalog-backend/src/database/operations/stitcher/buildEntitySearch.test.ts b/plugins/catalog-backend/src/database/operations/stitcher/buildEntitySearch.test.ts
index 4241599351..5a9e634e35 100644
--- a/plugins/catalog-backend/src/database/operations/stitcher/buildEntitySearch.test.ts
+++ b/plugins/catalog-backend/src/database/operations/stitcher/buildEntitySearch.test.ts
@@ -15,6 +15,7 @@
  */
 
 import { DEFAULT_NAMESPACE, Entity } from '@backstage/catalog-model';
+import { performance } from 'node:perf_hooks';
 import { buildEntitySearch, mapToRows, traverse } from './buildEntitySearch';
 
 describe('buildEntitySearch', () => {
@@ -50,6 +51,23 @@ describe('buildEntitySearch', () => {
       ]);
     });
 
+    it('handles large arrays without quadratic performance degradation', () => {
+      // Generate an array with 500 unique string items to verify that the
+      // Set-based dedup scales linearly rather than quadratically.
+      // With the previous Array.some() approach this would cause ~125,000
+      // comparisons; with Set.has() it's ~500 lookups.
+      const items = Array.from({ length: 500 }, (_, i) => `tag-${i}`);
+      const input = { tags: items };
+
+      const start = performance.now();
+      const output = traverse(input);
+      const elapsed = performance.now() - start;
+
+      expect(output).toHaveLength(1000);
+      // Should complete well under 100ms with O(n); O(n²) would be noticeably slower
+      expect(elapsed).toBeLessThan(100);
+    });
+
     it('skips over special keys', () => {
       const input = {
         status: { x: 1 },
diff --git a/plugins/catalog-backend/src/database/operations/stitcher/buildEntitySearch.ts b/plugins/catalog-backend/src/database/operations/stitcher/buildEntitySearch.ts
index bee0426a99..c8e09f3347 100644
--- a/plugins/catalog-backend/src/database/operations/stitcher/buildEntitySearch.ts
+++ b/plugins/catalog-backend/src/database/operations/stitcher/buildEntitySearch.ts
@@ -71,6 +71,11 @@ type Kv = {
 // "h.j": "l"
 export function traverse(root: unknown): Kv[] {
   const output: Kv[] = [];
+  // Use a Set for O(1) case-insensitive duplicate detection of synthetic
+  // boolean path keys (e.g. "metadata.tags.java"), instead of the previous
+  // O(n) Array.some() linear scan which caused O(n²) overall complexity
+  // and severe event loop blocking for entities with large arrays.
+  const seenPathKeys = new Set<string>();
 
   function visit(path: string, current: unknown) {
     if (SPECIAL_KEYS.includes(path)) {
@@ -111,13 +116,9 @@ export function traverse(root: unknown): Kv[] {
         visit(path, item);
         if (typeof item === 'string') {
           const pathKey = `${path}.${item}`;
-          if (
-            !output.some(
-              kv =>
-                kv.key.toLocaleLowerCase('en-US') ===
-                pathKey.toLocaleLowerCase('en-US'),
-            )
-          ) {
+          const lowerKey = pathKey.toLocaleLowerCase('en-US');
+          if (!seenPathKeys.has(lowerKey)) {
+            seenPathKeys.add(lowerKey);
             output.push({ key: pathKey, value: true });
           }
         }