diff --git a/.github/workflows/prod-build.yml b/.github/workflows/prod-build.yml
index 5a68d93e5507..19210702d04e 100644
--- a/.github/workflows/prod-build.yml
+++ b/.github/workflows/prod-build.yml
@@ -340,6 +340,7 @@ jobs:
         run: |-
           npm ci
           npm run build-redirects
+          npm run build-canonicals
 
       - name: Deploy Function
         if: ${{ ! vars.SKIP_FUNCTION }}
diff --git a/.github/workflows/stage-build.yml b/.github/workflows/stage-build.yml
index 7d9cf3b4fad3..c49aa7009736 100644
--- a/.github/workflows/stage-build.yml
+++ b/.github/workflows/stage-build.yml
@@ -356,6 +356,7 @@ jobs:
         run: |
           npm ci
           npm run build-redirects
+          npm run build-canonicals
 
       - name: Deploy Function
         if: ${{ ! vars.SKIP_FUNCTION }}
diff --git a/.github/workflows/xyz-build.yml b/.github/workflows/xyz-build.yml
index 4b86c2cb6581..2646a6a01b7d 100644
--- a/.github/workflows/xyz-build.yml
+++ b/.github/workflows/xyz-build.yml
@@ -237,6 +237,7 @@ jobs:
         run: |
           npm ci
           npm run build-redirects
+          npm run build-canonicals
 
       - name: Deploy Function
         if: ${{ ! vars.SKIP_FUNCTION }}
diff --git a/build/cli.ts b/build/cli.ts
index 6e44be356ed0..828da2ae248d 100644
--- a/build/cli.ts
+++ b/build/cli.ts
@@ -26,11 +26,10 @@ import {
 } from "./index.js";
 import { Doc, DocMetadata, Flaws } from "../libs/types/document.js";
 import SearchIndex from "./search-index.js";
-import { makeSitemapIndexXML, buildSitemap } from "./sitemaps.js";
+import { buildSitemapIndex, buildSitemap } from "./sitemaps.js";
 import { humanFileSize } from "./utils.js";
 import { initSentry } from "./sentry.js";
 import { macroRenderTimes } from "../kumascript/src/render.js";
-import { fdir } from "fdir";
 import { ssrDocument } from "./ssr.js";
 import { HydrationData } from "../libs/types/hydration.js";
 
@@ -515,25 +514,16 @@ program
         if (!options.quiet) {
           console.log(chalk.yellow("Building sitemap index file..."));
         }
-        const sitemapsBuilt = new fdir()
-          .filter((p) => p.endsWith("/sitemap.xml.gz"))
-          .withFullPaths()
-          .crawl(path.join(BUILD_OUT_ROOT, "sitemaps"))
-          .sync()
-          .sort()
-          .map((fp) => fp.replace(BUILD_OUT_ROOT, ""));
-        const sitemapIndexFilePath = path.join(BUILD_OUT_ROOT, "sitemap.xml");
-        fs.writeFileSync(
-          sitemapIndexFilePath,
-          makeSitemapIndexXML(sitemapsBuilt)
-        );
+        const sitemapsBuilt = await buildSitemapIndex();
 
         if (!options.quiet) {
-          console.log(
-            chalk.green(
-              `Wrote sitemap index referencing ${sitemapsBuilt.length} sitemaps:\n${sitemapsBuilt.map((s) => `- ${s}`).join("\n")}`
-            )
-          );
+          for (const sitemaps of sitemapsBuilt) {
+            console.log(
+              chalk.green(
+                `Wrote sitemap index referencing ${sitemaps.length} sitemaps:\n${sitemaps.map((s) => `- ${s}`).join("\n")}`
+              )
+            );
+          }
         }
         return;
       }
diff --git a/build/sitemaps.ts b/build/sitemaps.ts
index 59f1a028d22d..0bd1573da611 100644
--- a/build/sitemaps.ts
+++ b/build/sitemaps.ts
@@ -1,7 +1,9 @@
 import { join } from "node:path";
-import { mkdir, writeFile } from "node:fs/promises";
+import { mkdir, readFile, writeFile } from "node:fs/promises";
 import { gzipSync } from "node:zlib";
 
+import { fdir } from "fdir";
+
 import { BASE_URL, BUILD_OUT_ROOT } from "../libs/env/index.js";
 
 const SITEMAP_BASE_URL = BASE_URL.replace(/\/$/, "");
@@ -18,10 +20,61 @@ export async function buildSitemap(
     pathSuffix = [],
   }: { slugPrefix?: string; pathSuffix?: string[] }
 ) {
+  const txt = entries.map(({ slug }) => `${slugPrefix}${slug}`).join("\n");
   const xml = makeSitemapXML(slugPrefix, entries);
-  const path = await writeSitemap(xml, ...pathSuffix);
 
-  return path;
+  const dirPath = join(
+    BUILD_OUT_ROOT,
+    "sitemaps",
+    ...pathSuffix.map((p) => p.toLowerCase())
+  );
+  await mkdir(dirPath, { recursive: true });
+
+  const txtPath = join(dirPath, "sitemap.txt");
+  const xmlPath = join(dirPath, "sitemap.xml.gz");
+
+  await Promise.all([
+    writeFile(txtPath, txt, "utf-8"),
+    writeFile(xmlPath, gzipSync(xml)),
+  ]);
+
+  return xmlPath;
+}
+
+export async function buildSitemapIndex() {
+  return Promise.all([buildSitemapIndexTXT(), buildSitemapIndexXML()]);
+}
+
+export async function buildSitemapIndexTXT() {
+  const sitemaps = new fdir()
+    .filter((p) => p.endsWith("/sitemap.txt"))
+    .withFullPaths()
+    .crawl(join(BUILD_OUT_ROOT, "sitemaps"))
+    .sync();
+
+  const file = join(BUILD_OUT_ROOT, "sitemap.txt");
+
+  const content = await makeSitemapIndexTXT(sitemaps);
+
+  await writeFile(file, content, "utf-8");
+
+  return sitemaps.sort().map((fp) => fp.replace(BUILD_OUT_ROOT, ""));
+}
+
+export async function buildSitemapIndexXML() {
+  const sitemaps = new fdir()
+    .filter((p) => p.endsWith("/sitemap.xml.gz"))
+    .withFullPaths()
+    .crawl(join(BUILD_OUT_ROOT, "sitemaps"))
+    .sync()
+    .sort()
+    .map((fp) => fp.replace(BUILD_OUT_ROOT, ""));
+
+  const file = join(BUILD_OUT_ROOT, "sitemap.xml");
+
+  await writeFile(file, makeSitemapIndexXML(sitemaps));
+
+  return sitemaps.sort().map((fp) => fp.replace(BUILD_OUT_ROOT, ""));
 }
 
 function makeSitemapXML(prefix: string, docs: SitemapEntry[]) {
@@ -62,16 +115,13 @@ export function makeSitemapIndexXML(paths: string[]) {
   ].join("\n");
 }
 
-async function writeSitemap(xml: string, ...paths: string[]) {
-  const dirPath = join(
-    BUILD_OUT_ROOT,
-    "sitemaps",
-    ...paths.map((p) => p.toLowerCase())
-  );
-  await mkdir(dirPath, { recursive: true });
+/**
+ * Creates a global text sitemap by merging all text sitemaps.
+ */
+export async function makeSitemapIndexTXT(paths: string[]) {
+  const maps = await Promise.all(paths.map((p) => readFile(p, "utf-8")));
 
-  const filePath = join(dirPath, "sitemap.xml.gz");
-  await writeFile(filePath, gzipSync(xml));
+  const urls = maps.join("\n").split("\n").filter(Boolean);
 
-  return filePath;
+  return urls.sort().join("\n");
 }
diff --git a/build/spas.ts b/build/spas.ts
index cd358e712fe2..3972c69b769e 100644
--- a/build/spas.ts
+++ b/build/spas.ts
@@ -135,7 +135,10 @@ export async function buildSPAs(options: {
       continue;
     }
     for (const pathLocale of fs.readdirSync(root)) {
-      if (!fs.statSync(path.join(root, pathLocale)).isDirectory()) {
+      if (
+        !fs.statSync(path.join(root, pathLocale)).isDirectory() ||
+        !isValidLocale(pathLocale)
+      ) {
         continue;
       }
 
diff --git a/cloud-function/.gcloudignore b/cloud-function/.gcloudignore
index 79b725a2ebad..7ddddcfa0d05 100644
--- a/cloud-function/.gcloudignore
+++ b/cloud-function/.gcloudignore
@@ -15,5 +15,6 @@
 .gitignore
 
 #!include:.gitignore
+!canonicals.json
 !redirects.json
 !src/internal/**
diff --git a/cloud-function/.gitignore b/cloud-function/.gitignore
index deb96650c7f6..57c8cd36b4ca 100644
--- a/cloud-function/.gitignore
+++ b/cloud-function/.gitignore
@@ -2,6 +2,7 @@ node_modules
 .env*
 !.env-dist
 *.log
+canonicals.json
 redirects.json
 src/**/*.js
 src/internal
diff --git a/cloud-function/package.json b/cloud-function/package.json
index cd0c717f0430..b34347f0f95f 100644
--- a/cloud-function/package.json
+++ b/cloud-function/package.json
@@ -9,6 +9,7 @@
   "main": "src/index.js",
   "scripts": {
     "build": "tsc -b",
+    "build-canonicals": "cross-env NODE_OPTIONS='--no-warnings=ExperimentalWarning --loader ts-node/esm' node src/build-canonicals.ts",
     "build-redirects": "cross-env NODE_OPTIONS='--no-warnings=ExperimentalWarning --loader ts-node/esm' node src/build-redirects.ts",
     "copy-internal": "rm -rf ./src/internal && cp -R ../libs ./src/internal",
     "gcp-build": "npm run build",
diff --git a/cloud-function/src/app.ts b/cloud-function/src/app.ts
index 66019a394427..1f7221f70d4f 100644
--- a/cloud-function/src/app.ts
+++ b/cloud-function/src/app.ts
@@ -10,6 +10,7 @@ import { handleStripePlans } from "./handlers/handle-stripe-plans.js";
 import { proxyTelemetry } from "./handlers/proxy-telemetry.js";
 import { lowercasePathname } from "./middlewares/lowercase-pathname.js";
 import { resolveIndexHTML } from "./middlewares/resolve-index-html.js";
+import { redirectNonCanonicals } from "./middlewares/redirect-non-canonicals.js";
 import { redirectLeadingSlash } from "./middlewares/redirect-leading-slash.js";
 import { redirectMovedPages } from "./middlewares/redirect-moved-pages.js";
 import { redirectEnforceTrailingSlash } from "./middlewares/redirect-enforce-trailing-slash.js";
@@ -26,43 +27,59 @@ import { proxyPong } from "./handlers/proxy-pong.js";
 const router = Router();
 router.use(stripForwardedHostHeaders);
 router.use(redirectLeadingSlash);
+// MDN Plus plans.
 router.all(
   "/api/v1/stripe/plans",
   requireOrigin(Origin.main),
   handleStripePlans
 );
+// Backend.
 router.all(
   ["/api/*", "/admin-api/*", "/events/fxa", "/users/fxa/*"],
   requireOrigin(Origin.main),
   proxyApi
 );
+// Telemetry.
 router.all("/submit/mdn-yari/*", requireOrigin(Origin.main), proxyTelemetry);
 router.all("/pong/*", requireOrigin(Origin.main), express.json(), proxyPong);
 router.all("/pimg/*", requireOrigin(Origin.main), proxyPong);
+// Playground.
 router.get(
   ["/[^/]+/docs/*/runner.html", "/[^/]+/blog/*/runner.html", "/runner.html"],
   requireOrigin(Origin.play),
   resolveRunnerHtml,
   proxyRunner
 );
+// Assets.
 router.get(
   ["/assets/*", "/sitemaps/*", "/static/*", "/[^/]+.[^/]+"],
   requireOrigin(Origin.main),
   proxyContent
 );
+router.get(
+  "/[^/]+/search-index.json",
+  requireOrigin(Origin.main),
+  lowercasePathname,
+  proxyContent
+);
+// Root.
 router.get("/", requireOrigin(Origin.main), redirectLocale);
+// Live samples.
 router.get(
   ["/[^/]+/docs/*/_sample_.*.html", "/[^/]+/blog/*/_sample_.*.html"],
   requireOrigin(Origin.liveSamples),
   resolveIndexHTML,
   proxyContent
 );
+// Attachments.
 router.get(
   `/[^/]+/docs/*/*.(${ANY_ATTACHMENT_EXT.join("|")})`,
   requireOrigin(Origin.main, Origin.liveSamples, Origin.play),
   resolveIndexHTML,
   proxyContent
 );
+// Pages.
+router.use(redirectNonCanonicals);
 router.get(
   "/[^/]+/docs/*",
   requireOrigin(Origin.main),
@@ -81,12 +98,7 @@ router.get(
   resolveIndexHTML,
   proxyContent
 );
-router.get(
-  "/[^/]+/search-index.json",
-  requireOrigin(Origin.main),
-  lowercasePathname,
-  proxyContent
-);
+// MDN Plus, static pages, etc.
 router.get(
   "*",
   requireOrigin(Origin.main),
diff --git a/cloud-function/src/build-canonicals.ts b/cloud-function/src/build-canonicals.ts
new file mode 100644
index 000000000000..b5fdd6a484ee
--- /dev/null
+++ b/cloud-function/src/build-canonicals.ts
@@ -0,0 +1,40 @@
+import { readFile, stat, writeFile } from "node:fs/promises";
+import { dirname, join } from "node:path";
+import { fileURLToPath } from "node:url";
+
+import * as dotenv from "dotenv";
+
+import { normalizePath } from "./utils.js";
+
+const __dirname = dirname(fileURLToPath(import.meta.url));
+
+const root = join(__dirname, "..", "..");
+dotenv.config({
+  path: join(root, process.env["ENV_FILE"] || ".env"),
+});
+
+async function buildCanonicals() {
+  const { BUILD_OUT_ROOT = join(root, "client", "build") } = process.env;
+
+  const sitemapPath = join(BUILD_OUT_ROOT, "sitemap.txt");
+
+  const content = await readFile(sitemapPath, "utf-8");
+  const lines = content.split("\n");
+  const pages = lines.filter((line) => line.startsWith("/"));
+
+  const siteMap: Record<string, string> = {};
+  for (const page of pages) {
+    siteMap[normalizePath(page)] = page;
+  }
+  console.log(`- ${sitemapPath}: ${pages.length} pages`);
+
+  const output = "canonicals.json";
+
+  await writeFile(output, JSON.stringify(siteMap));
+
+  const count = Object.keys(siteMap).length;
+  const kb = Math.round((await stat(output)).size / 1024);
+  console.log(`Wrote ${count} pages in ${kb} KB.`);
+}
+
+await buildCanonicals();
diff --git a/cloud-function/src/middlewares/redirect-non-canonicals.ts b/cloud-function/src/middlewares/redirect-non-canonicals.ts
new file mode 100644
index 000000000000..a2abc9514822
--- /dev/null
+++ b/cloud-function/src/middlewares/redirect-non-canonicals.ts
@@ -0,0 +1,46 @@
+import { createRequire } from "node:module";
+
+import { NextFunction, Request, Response } from "express";
+
+import { THIRTY_DAYS } from "../constants.js";
+import { normalizePath, redirect } from "../utils.js";
+
+const require = createRequire(import.meta.url);
+const REDIRECTS = require("../../canonicals.json");
+const REDIRECT_SUFFIXES = ["/index.json", "/bcd.json", ""];
+
+export async function redirectNonCanonicals(
+  req: Request,
+  res: Response,
+  next: NextFunction
+) {
+  const parsedUrl = new URL(req.url, `${req.protocol}://${req.headers.host}/`);
+  const { pathname } = parsedUrl;
+
+  // Redirect to canonical version.
+  // Example:
+  // - Source: /en-US/docs/web/guide/ajax/getting_started
+  // - Target: /en-US/docs/Web/Guide/AJAX/Getting_Started
+  for (const suffix of REDIRECT_SUFFIXES) {
+    if (!pathname.endsWith(suffix)) {
+      continue;
+    }
+    const originalSource = pathname.substring(
+      0,
+      pathname.length - suffix.length
+    );
+    const source = normalizePath(originalSource);
+    if (
+      typeof REDIRECTS[source] == "string" &&
+      REDIRECTS[source] !== originalSource
+    ) {
+      const target = REDIRECTS[source] + suffix + parsedUrl.search;
+      return redirect(res, target, {
+        status: 301,
+        cacheControlSeconds: THIRTY_DAYS,
+      });
+    }
+  }
+
+  next();
+}
diff --git a/cloud-function/src/utils.ts b/cloud-function/src/utils.ts
index 34f0060d6608..893570e09736 100644
--- a/cloud-function/src/utils.ts
+++ b/cloud-function/src/utils.ts
@@ -59,3 +59,7 @@ const ANY_ATTACHMENT_REGEXP = createRegExpFromExtensions(
 export function isAsset(url: string) {
   return ANY_ATTACHMENT_REGEXP.test(url);
 }
+
+export function normalizePath(path: string) {
+  return path.toLowerCase().replace(/\/$/, "");
+}