diff --git a/src/config/seo.ts b/src/config/seo.ts
new file mode 100644
index 0000000..aec9753
--- /dev/null
+++ b/src/config/seo.ts
@@ -0,0 +1,7 @@
+export const seoConfig = {
+  lastmod: "2025-06-01T00:00:00Z",
+} as const;
+
+export function getLastmod(): string {
+  return process.env.SITEMAP_LASTMOD ?? seoConfig.lastmod;
+}
diff --git a/src/pages/robots.txt.ts b/src/pages/robots.txt.ts
index 8e2d3dd..d8c93d8 100644
--- a/src/pages/robots.txt.ts
+++ b/src/pages/robots.txt.ts
@@ -1,5 +1,5 @@
 import type { APIRoute } from "astro";
-import { siteConfig } from "../config/site";
+import { siteConfig } from "@/config/site";
 
 export const GET: APIRoute = () => {
   const robotsTxt = `User-agent: *
diff --git a/src/pages/sitemap.xml.ts b/src/pages/sitemap.xml.ts
index 557aa8d..dd9dd4b 100644
--- a/src/pages/sitemap.xml.ts
+++ b/src/pages/sitemap.xml.ts
@@ -1,27 +1,33 @@
 import type { APIRoute } from "astro";
-import { siteConfig } from "../config/site";
+import { siteConfig } from "@/config/site";
+import { getLastmod } from "@/config/seo";
+
+const ALWAYS = [
+  { loc: siteConfig.url, priority: "1.0" },
+  { loc: `${siteConfig.url}/downloads`, priority: "0.8" },
+];
 
 export const GET: APIRoute = () => {
+  const lastmod = getLastmod();
+
+  const urls = ALWAYS.map(
+    (page) => `  <url>
+    <loc>${page.loc}</loc>
+    <lastmod>${lastmod}</lastmod>
+    <changefreq>weekly</changefreq>
+    <priority>${page.priority}</priority>
+  </url>`
+  ).join("\n");
+
   const sitemap = `<?xml version="1.0" encoding="UTF-8"?>
 <urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
-  <url>
-    <loc>${siteConfig.url}</loc>
-    <lastmod>${new Date().toISOString()}</lastmod>
-    <changefreq>weekly</changefreq>
-    <priority>1.0</priority>
-  </url>
-  <url>
-    <loc>${siteConfig.url}/downloads</loc>
-    <lastmod>${new Date().toISOString()}</lastmod>
-    <changefreq>weekly</changefreq>
-    <priority>0.8</priority>
-  </url>
-</urlset>
-`;
+${urls}
+</urlset>`;
 
   return new Response(sitemap, {
     headers: {
       "Content-Type": "application/xml; charset=utf-8",
+      "Cache-Control": "public, max-age=86400, s-maxage=3600",
     },
   });
 };