diff --git a/app/lib/shared/sitemap.test.ts b/app/lib/shared/sitemap.test.ts
new file mode 100644
index 0000000..5080eff
--- /dev/null
+++ b/app/lib/shared/sitemap.test.ts
@@ -0,0 +1,25 @@
+import { describe, expect, it } from "vite-plus/test";
+
+import { buildRobotsTxt, buildSitemapXml } from "./sitemap";
+
+describe("buildSitemapXml", () => {
+  it("パスを origin つきの絶対URLにして loc に入れる", () => {
+    const xml = buildSitemapXml("https://example.com", ["/", "/login"]);
+    expect(xml).toContain("<loc>https://example.com/</loc>");
+    expect(xml).toContain("<loc>https://example.com/login</loc>");
+  });
+
+  it("XML の特殊文字をエスケープする", () => {
+    expect(buildSitemapXml("https://example.com", ["/a?x=1&y=2"])).toContain(
+      "<loc>https://example.com/a?x=1&amp;y=2</loc>",
+    );
+  });
+});
+
+describe("buildRobotsTxt", () => {
+  it("Disallow と sitemap の絶対URLを書く", () => {
+    const txt = buildRobotsTxt("https://example.com", ["/api/"]);
+    expect(txt).toContain("Disallow: /api/");
+    expect(txt).toContain("Sitemap: https://example.com/sitemap.xml");
+  });
+});
diff --git a/app/lib/shared/sitemap.ts b/app/lib/shared/sitemap.ts
new file mode 100644
index 0000000..1cb3668
--- /dev/null
+++ b/app/lib/shared/sitemap.ts
@@ -0,0 +1,42 @@
+// 検索エンジン（Googleのクローラなど）に渡す sitemap.xml・robots.txt を組み立てる。
+// /learn や /my-notebooks などはログイン必須でクローラが読めないため、未ログインで見られるページだけを載せる
+export const SITEMAP_PATHS = ["/", "/login", "/signup"] as const;
+
+// クローラに辿らせないパス。API とログイン必須のページ
+export const ROBOTS_DISALLOW_PATHS = [
+  "/api/",
+  "/history",
+  "/learn",
+  "/my-notebooks",
+  "/invite/",
+] as const;
+
+function escapeXml(value: string): string {
+  return value
+    .replace(/&/g, "&amp;")
+    .replace(/</g, "&lt;")
+    .replace(/>/g, "&gt;")
+    .replace(/"/g, "&quot;")
+    .replace(/'/g, "&apos;");
+}
+
+// origin（例: https://example.com）と パスの一覧から sitemap.xml の本文を返す
+export function buildSitemapXml(origin: string, paths: readonly string[]): string {
+  const urls = paths
+    .map((path) => `  <url><loc>${escapeXml(new URL(path, origin).toString())}</loc></url>`)
+    .join("\n");
+  return `<?xml version="1.0" encoding="UTF-8"?>
+<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
+${urls}
+</urlset>
+`;
+}
+
+export function buildRobotsTxt(origin: string, disallowPaths: readonly string[]): string {
+  const disallow = disallowPaths.map((path) => `Disallow: ${path}`).join("\n");
+  return `User-agent: *
+${disallow}
+
+Sitemap: ${new URL("/sitemap.xml", origin).toString()}
+`;
+}
diff --git a/app/routes/robots[.]txt/route.ts b/app/routes/robots[.]txt/route.ts
new file mode 100644
index 0000000..e699ac0
--- /dev/null
+++ b/app/routes/robots[.]txt/route.ts
@@ -0,0 +1,15 @@
+import { buildRobotsTxt, ROBOTS_DISALLOW_PATHS } from "@/lib/shared/sitemap";
+
+// 検索エンジン向けの /robots.txt。sitemap.xml の場所もここで知らせる
+export function loader() {
+  const txt = buildRobotsTxt(
+    process.env.BETTER_AUTH_URL ?? "http://localhost:3000",
+    ROBOTS_DISALLOW_PATHS,
+  );
+  return new Response(txt, {
+    headers: {
+      "Content-Type": "text/plain; charset=utf-8",
+      "Cache-Control": "public, max-age=3600",
+    },
+  });
+}
diff --git a/app/routes/sitemap[.]xml/route.ts b/app/routes/sitemap[.]xml/route.ts
new file mode 100644
index 0000000..72a0c47
--- /dev/null
+++ b/app/routes/sitemap[.]xml/route.ts
@@ -0,0 +1,15 @@
+import { buildSitemapXml, SITEMAP_PATHS } from "@/lib/shared/sitemap";
+
+// 検索エンジン向けの /sitemap.xml。アプリのオリジンは認証と同じ環境変数を使う
+export function loader() {
+  const xml = buildSitemapXml(
+    process.env.BETTER_AUTH_URL ?? "http://localhost:3000",
+    SITEMAP_PATHS,
+  );
+  return new Response(xml, {
+    headers: {
+      "Content-Type": "application/xml; charset=utf-8",
+      "Cache-Control": "public, max-age=3600",
+    },
+  });
+}