diff --git a/js/project-loader.js b/js/project-loader.js
index 7d41c88..9160089 100644
--- a/js/project-loader.js
+++ b/js/project-loader.js
@@ -55,15 +55,16 @@ const limitProjectsForPage = (projects, pathname) => {
 };
 
 /**
- * Prepares projects for display (sort + limit)
+ * Prepares projects for display (drop hidden + sort + limit)
  * Pure function
- * 
+ *
  * @param {Array<Object>} projects - Raw projects array
  * @param {string} pathname - Window location pathname
  * @returns {Array<Object>} - Prepared projects
  */
 const prepareProjects = (projects, pathname) => {
-  const sorted = sortProjects(projects);
+  const visible = projects.filter(project => project.hidden !== true);
+  const sorted = sortProjects(visible);
   return limitProjectsForPage(sorted, pathname);
 };
 
diff --git a/projects/projects-data.json b/projects/projects-data.json
index 47942dc..8b0aa13 100644
--- a/projects/projects-data.json
+++ b/projects/projects-data.json
@@ -61,6 +61,7 @@
       "liveUrl": "https://www.emilysueanderson.com/io-puzzle-2025-solutions",
       "blogPostUrl": "/blog/solving-io-puzzles-2025/",
       "featured": false,
+      "hidden": true,
       "completionDate": "2025-03"
     },
     {
diff --git a/scripts/index-all-content.js b/scripts/index-all-content.js
index 96fa9dd..3a0e32c 100644
--- a/scripts/index-all-content.js
+++ b/scripts/index-all-content.js
@@ -63,6 +63,17 @@ function getBlogPostUrls() {
   }
 }
 
+/**
+ * Map project entries to their URLs, skipping hidden ones (they are not
+ * listed on the site, matching js/project-loader.js)
+ */
+function projectUrls(projects) {
+  return projects.filter(project => project.hidden !== true).map(project => {
+    // Projects use 'id' not 'slug'
+    return `${SITE_BASE_URL}/projects/${project.id}/`;
+  });
+}
+
 /**
  * Get all project URLs
  */
@@ -74,10 +85,7 @@ function getProjectUrls() {
     }
 
     const projectsData = JSON.parse(fs.readFileSync(PATHS.projectsData, 'utf8'));
-    return (projectsData.projects || []).map(project => {
-      // Projects use 'id' not 'slug'
-      return `${SITE_BASE_URL}/projects/${project.id}/`;
-    });
+    return projectUrls(projectsData.projects || []);
   } catch (error) {
     console.error('Error reading projects data:', error.message);
     return [];
@@ -251,7 +259,12 @@ async function main() {
   }
 }
 
-main().catch(error => {
-  console.error('Fatal error:', error.message);
-  process.exit(1);
-});
+module.exports = { projectUrls };
+
+// Only submit when run directly, not when require()'d from a test.
+if (require.main === module) {
+  main().catch(error => {
+    console.error('Fatal error:', error.message);
+    process.exit(1);
+  });
+}
diff --git a/sitemap.xml b/sitemap.xml
index 808c4eb..99c02ec 100644
--- a/sitemap.xml
+++ b/sitemap.xml
@@ -256,17 +256,6 @@
     </image:image>
   </url>
 
-  <url>
-    <loc>https://helloemily.dev/projects/io-puzzle-2025/</loc>
-    <lastmod>2026-01-13</lastmod>
-    <changefreq>never</changefreq>
-    <priority>0.8</priority>
-    <image:image>
-      <image:loc>https://helloemily.dev/projects/io-puzzle-2025/io-puzzle-1.jpeg</image:loc>
-      <image:title>I/O Puzzle 2025 Solutions</image:title>
-    </image:image>
-  </url>
-
   <url>
     <loc>https://helloemily.dev/projects/sean-cameron-website/</loc>
     <lastmod>2026-01-13</lastmod>
diff --git a/tests/index-all-content.test.js b/tests/index-all-content.test.js
new file mode 100644
index 0000000..52d299f
--- /dev/null
+++ b/tests/index-all-content.test.js
@@ -0,0 +1,31 @@
+/**
+ * Tests for the search indexing script's project URLs
+ */
+
+import { describe, it, expect } from 'vitest';
+import { createRequire } from 'module';
+import { readFileSync } from 'fs';
+
+const require = createRequire(import.meta.url);
+const { projectUrls } = require('../scripts/index-all-content.js');
+
+describe('index-all-content projectUrls', () => {
+  it('maps visible projects to their project URLs and skips hidden ones', () => {
+    const projects = [
+      { id: 'shown' },
+      { id: 'gone', hidden: true },
+      { id: 'also-shown', hidden: false },
+    ];
+
+    expect(projectUrls(projects)).toEqual([
+      'https://helloemily.dev/projects/shown/',
+      'https://helloemily.dev/projects/also-shown/',
+    ]);
+  });
+
+  it('does not submit the hidden io-puzzle-2025 project from projects-data.json', () => {
+    const { projects } = JSON.parse(readFileSync('projects/projects-data.json', 'utf8'));
+
+    expect(projectUrls(projects)).not.toContain('https://helloemily.dev/projects/io-puzzle-2025/');
+  });
+});
diff --git a/tests/project-loader.test.js b/tests/project-loader.test.js
new file mode 100644
index 0000000..0809f55
--- /dev/null
+++ b/tests/project-loader.test.js
@@ -0,0 +1,67 @@
+/**
+ * Tests for the project loader's display preparation
+ */
+
+import { describe, it, expect } from 'vitest';
+import { readFileSync } from 'fs';
+import { prepareProjects } from '../js/project-loader.js';
+
+const project = (id, overrides = {}) => ({
+  id,
+  featured: false,
+  completionDate: '2025-01',
+  ...overrides,
+});
+
+describe('Project Loader', () => {
+  describe('prepareProjects', () => {
+    it('omits hidden projects on the projects page', () => {
+      const projects = [
+        project('shown-a', { completionDate: '2025-03' }),
+        project('hidden', { hidden: true, featured: true }),
+        project('shown-b', { completionDate: '2025-01' }),
+      ];
+
+      const ids = prepareProjects(projects, '/pages/projects.html').map((p) => p.id);
+
+      expect(ids).toEqual(['shown-a', 'shown-b']);
+    });
+
+    it('fills all three home page slots from visible projects when one is hidden', () => {
+      const projects = [
+        project('hidden', { hidden: true, featured: true, completionDate: '2025-06' }),
+        project('p1', { completionDate: '2025-05' }),
+        project('p2', { completionDate: '2025-04' }),
+        project('p3', { completionDate: '2025-03' }),
+        project('p4', { completionDate: '2025-02' }),
+      ];
+
+      const ids = prepareProjects(projects, '/').map((p) => p.id);
+
+      expect(ids).toEqual(['p1', 'p2', 'p3']);
+    });
+
+    it('keeps projects with hidden set to false or absent', () => {
+      const projects = [
+        project('explicit', { hidden: false, completionDate: '2025-02' }),
+        project('absent', { completionDate: '2025-01' }),
+      ];
+
+      const ids = prepareProjects(projects, '/pages/projects.html').map((p) => p.id);
+
+      expect(ids).toEqual(['explicit', 'absent']);
+    });
+  });
+
+  describe('projects-data.json', () => {
+    const { projects } = JSON.parse(readFileSync('projects/projects-data.json', 'utf8'));
+
+    it('does not display any project linking to emilysueanderson.com', () => {
+      const displayed = prepareProjects(projects, '/pages/projects.html');
+
+      const offending = displayed.filter((p) => /emilysueanderson\.com/i.test(JSON.stringify(p)));
+
+      expect(offending.map((p) => p.id)).toEqual([]);
+    });
+  });
+});