diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 855acc6..1dfd3ef 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -20,6 +20,10 @@ jobs:
         run: npm test
       - name: Lint
         run: npm run lint
+      # Blocking: catches structural HTML errors (e.g. an unescaped " that
+      # terminates an attribute) that node --check + vitest + eslint can't see.
+      - name: HTML parse check
+        run: npm run check:html
       - name: Format check (advisory)
         run: npm run format:check
         continue-on-error: true
diff --git a/eslint.config.js b/eslint.config.js
index 7b0b7a7..ab1cfc8 100644
--- a/eslint.config.js
+++ b/eslint.config.js
@@ -28,4 +28,10 @@ export default [
     files: ['tests/**/*.js'],
     languageOptions: { globals: { ...globals.node, ...globals.browser } },
   },
+  {
+    // CLI tooling (e.g. the HTML parse gate) reports via stdout/stderr by design.
+    files: ['tools/**/*.{js,mjs}'],
+    languageOptions: { globals: { ...globals.node } },
+    rules: { 'no-console': 'off' },
+  },
 ];
diff --git a/library.html b/library.html
index ce71db4..87deb4e 100644
--- a/library.html
+++ b/library.html
@@ -613,7 +613,7 @@ <h1>Library</h1><span class="count" id="count"></span>
       </select>
     </div>
     <form class="lib-ask" id="ask-bar" autocomplete="off" onsubmit="return false">
-      <input class="lib-ask-input" id="ask-input" type="text" placeholder="Ask your library… e.g. "What's my best SSR option?"" aria-label="Ask a question about your saved repos">
+      <input class="lib-ask-input" id="ask-input" type="text" placeholder="Ask your library… e.g. &quot;What's my best SSR option?&quot;" aria-label="Ask a question about your saved repos">
       <button class="lib-ask-btn" id="ask-btn" type="button">Ask</button>
     </form>
     <div class="lib-ask-answer hidden" id="ask-answer" role="region" aria-label="Ask answer" aria-live="polite"></div>
diff --git a/package.json b/package.json
index 1635850..274145d 100644
--- a/package.json
+++ b/package.json
@@ -8,6 +8,7 @@
     "test:coverage": "vitest run --coverage",
     "lint": "eslint .",
     "lint:fix": "eslint . --fix",
+    "check:html": "node tools/check-html.mjs",
     "format": "prettier --write \"**/*.{js,json,css,html,md}\"",
     "format:check": "prettier --check \"**/*.{js,json,css,html,md}\""
   },
diff --git a/tools/check-html.mjs b/tools/check-html.mjs
new file mode 100644
index 0000000..3c48196
--- /dev/null
+++ b/tools/check-html.mjs
@@ -0,0 +1,41 @@
+#!/usr/bin/env node
+// HTML parse-validity gate.
+//
+// Fails ONLY on a true parse error (e.g. an unescaped quote that terminates an
+// attribute early), NOT on formatting drift — that stays advisory via the
+// `format:check` script. This closes the blind spot that let attribute-quote
+// bugs ship in options.html and library.html past node --check + vitest + eslint
+// (none of which look at HTML).
+//
+// Uses prettier's parser via its Node API: prettier.format() throws on a parse
+// error and merely reformats on style differences, so a thrown error is a real
+// structural problem, not a whitespace nit.
+
+import prettier from 'prettier';
+import { readFileSync } from 'node:fs';
+import { execSync } from 'node:child_process';
+
+const files = execSync('git ls-files "*.html"', { encoding: 'utf8' })
+  .trim()
+  .split('\n')
+  .filter(Boolean);
+
+const failures = [];
+for (const file of files) {
+  try {
+    await prettier.format(readFileSync(file, 'utf8'), { parser: 'html', filepath: file });
+  } catch (err) {
+    failures.push({ file, message: String(err.message).split('\n')[0] });
+  }
+}
+
+if (failures.length > 0) {
+  console.error(`HTML parse check FAILED — ${failures.length} file(s) with structural errors:\n`);
+  for (const { file, message } of failures) {
+    console.error(`  ${file}: ${message}`);
+  }
+  console.error('\nThese are real parse errors (often an unescaped " inside an attribute). Fix the markup.');
+  process.exit(1);
+}
+
+console.log(`HTML parse check passed — ${files.length} file(s) parse cleanly.`);