diff --git a/index.html b/index.html
index b30c9353..04c80141 100644
--- a/index.html
+++ b/index.html
@@ -65,8 +65,8 @@
         });
       }
     </script>
+    <!-- Normalize path-based URLs before HashRouter starts. -->
     <script>
-      // Redirect non-hash URLs before the app bundle is requested.
       if (
         window.location.protocol !== 'file:' &&
         window.location.pathname &&
diff --git a/vercel.json b/vercel.json
index 336aa0a0..c2fb51b1 100644
--- a/vercel.json
+++ b/vercel.json
@@ -43,7 +43,7 @@
         { "key": "Strict-Transport-Security", "value": "max-age=31536000; includeSubDomains" },
         {
           "key": "Content-Security-Policy",
-          "value": "default-src 'self'; base-uri 'none'; object-src 'none'; form-action 'self'; frame-ancestors 'none'; script-src 'self' 'wasm-unsafe-eval' 'sha256-kF+BgNpp0e7WM8m8a9eRaLHmLrSQGQVmaFYjvPYU1/8=' 'sha256-kiz84y15tsP8n+Qo/YHYAPLBR6nQyVSqHO4BWcVVOik=' https://platform.twitter.com https://embed.reddit.com https://www.tiktok.com https://www.instagram.com; style-src 'self' 'unsafe-inline'; img-src 'self' https: http: data: blob:; media-src 'self' https: http: blob:; connect-src 'self' https: http: wss: ws: blob:; frame-src https: http://localhost:* http://*.localhost:* http://127.0.0.1:* http://[::1]:*; child-src https: http://localhost:* http://*.localhost:* http://127.0.0.1:* http://[::1]:*; worker-src 'self' blob:; manifest-src 'self'"
+          "value": "default-src 'self'; base-uri 'none'; object-src 'none'; form-action 'self'; frame-ancestors 'none'; script-src 'self' 'wasm-unsafe-eval' 'sha256-kF+BgNpp0e7WM8m8a9eRaLHmLrSQGQVmaFYjvPYU1/8=' 'sha256-uIRmdbN2zhK9eOgX0W2eTHZJSiH88uiZBeEZTwCIUyI=' https://platform.twitter.com https://embed.reddit.com https://www.tiktok.com https://www.instagram.com; style-src 'self' 'unsafe-inline'; img-src 'self' https: http: data: blob:; media-src 'self' https: http: blob:; connect-src 'self' https: http: wss: ws: blob:; frame-src https: http://localhost:* http://*.localhost:* http://127.0.0.1:* http://[::1]:*; child-src https: http://localhost:* http://*.localhost:* http://127.0.0.1:* http://[::1]:*; worker-src 'self' blob:; manifest-src 'self'"
         },
         { "key": "X-DNS-Prefetch-Control", "value": "off" }
       ]
diff --git a/vite.config.js b/vite.config.js
index 258e1a96..e3d70e9a 100644
--- a/vite.config.js
+++ b/vite.config.js
@@ -2,6 +2,7 @@ import { defineConfig } from 'vite';
 import react from '@vitejs/plugin-react';
 import { resolve } from 'path';
 import { readFileSync } from 'fs';
+import { createHash } from 'crypto';
 import { VitePWA } from 'vite-plugin-pwa';
 
 const { version: packageVersion } = JSON.parse(readFileSync(new URL('./package.json', import.meta.url), 'utf8'));
@@ -97,6 +98,55 @@ function appVersionMetadataPlugin() {
   };
 }
 
+function getVercelContentSecurityPolicy() {
+  const vercelConfig = JSON.parse(readFileSync(new URL('./vercel.json', import.meta.url), 'utf8'));
+  const cspHeader = vercelConfig.headers
+    ?.flatMap((entry) => entry.headers || [])
+    .find((header) => typeof header.key === 'string' && header.key.toLowerCase() === 'content-security-policy');
+
+  if (typeof cspHeader?.value !== 'string') {
+    throw new Error('vercel.json is missing a Content-Security-Policy header.');
+  }
+
+  return cspHeader.value;
+}
+
+function getInlineScriptHashes(indexHtml) {
+  const scriptPattern = /<script\b([^>]*)>([\s\S]*?)<\/script>/gi;
+  const hashes = [];
+
+  for (const [, attributes, source] of indexHtml.matchAll(scriptPattern)) {
+    if (/\bsrc\s*=/i.test(attributes) || source.trim().length === 0) {
+      continue;
+    }
+
+    hashes.push(`sha256-${createHash('sha256').update(source).digest('base64')}`);
+  }
+
+  return [...new Set(hashes)];
+}
+
+function verifyVercelCspHashesPlugin() {
+  return {
+    name: 'fivechan-verify-vercel-csp-hashes',
+    apply: 'build',
+    enforce: 'post',
+    closeBundle() {
+      const indexHtml = readFileSync(new URL(`./${buildOutDir}/index.html`, import.meta.url), 'utf8');
+      const contentSecurityPolicy = getVercelContentSecurityPolicy();
+      const missingHashes = getInlineScriptHashes(indexHtml).filter(
+        (hash) => !contentSecurityPolicy.includes(`'${hash}'`) && !contentSecurityPolicy.includes(hash),
+      );
+
+      if (missingHashes.length > 0) {
+        const plural = missingHashes.length === 1 ? '' : 'es';
+
+        throw new Error(`vercel.json Content-Security-Policy is missing inline script hash${plural}: ${missingHashes.join(', ')}`);
+      }
+    },
+  };
+}
+
 function adaptReactPluginForRolldown(plugin) {
   if (!plugin?.config || plugin.name !== 'vite:react-babel') {
     return plugin;
@@ -252,6 +302,7 @@ export default defineConfig({
         ],
       },
     }),
+    verifyVercelCspHashesPlugin(),
   ],
   resolve: {
     alias: {