diff --git a/frontend/shell-consistency.test.js b/frontend/shell-consistency.test.js
new file mode 100644
index 0000000..752875f
--- /dev/null
+++ b/frontend/shell-consistency.test.js
@@ -0,0 +1,29 @@
+const { test } = require('node:test');
+const assert = require('node:assert/strict');
+const { readFileSync, existsSync } = require('node:fs');
+const { join } = require('node:path');
+
+const root = join(__dirname, '..');
+const html = readFileSync(join(__dirname, 'index.html'), 'utf8');
+const sw = readFileSync(join(__dirname, 'sw.js'), 'utf8');
+const shellMatch = sw.match(/const SHELL = \[([\s\S]*?)\n\];/);
+assert.ok(shellMatch, 'service worker SHELL list is present');
+const shell = [...shellMatch[1].matchAll(/['"](\/[^'"]+)['"]/g)].map((match) => match[1]);
+const listed = new Set(shell);
+
+test('every local script and stylesheet in index.html is precached by the service worker', () => {
+  const localAssets = [];
+  for (const match of html.matchAll(/<(?:script\b[^>]*\bsrc|link\b[^>]*\bhref)="([^"]+)"/gi)) {
+    const url = match[1];
+    if (/^(?:[a-z]+:|\/|#)/i.test(url)) continue;
+    if (!/\.(?:js|css)(?:[?#]|$)/i.test(url)) continue;
+    localAssets.push(`/${url.split(/[?#]/, 1)[0]}`);
+  }
+  assert.ok(localAssets.length > 0, 'found local script/style assets');
+  for (const asset of localAssets) assert.ok(listed.has(asset), `${asset} appears in SHELL`);
+});
+
+test('every SHELL asset exists on disk and there are no duplicate entries', () => {
+  assert.equal(new Set(shell).size, shell.length, 'SHELL has no duplicate entries');
+  for (const asset of shell) assert.ok(existsSync(join(__dirname, asset.slice(1))), `${asset} exists`);
+});