diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
new file mode 100644
index 0000000..2af178d
--- /dev/null
+++ b/.github/workflows/ci.yml
@@ -0,0 +1,32 @@
+name: CI
+
+on:
+  pull_request:
+    branches:
+      - main
+  push:
+    branches:
+      - main
+
+permissions:
+  contents: read
+
+jobs:
+  build-and-validate:
+    name: Build and validate documentation
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check out repository
+        uses: actions/checkout@v4
+
+      - name: Set up Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: 22
+          cache: npm
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Build and validate documentation
+        run: npm run build
diff --git a/package.json b/package.json
index abdc7e8..b320526 100644
--- a/package.json
+++ b/package.json
@@ -3,8 +3,10 @@
   "private": true,
   "type": "module",
   "scripts": {
-    "build": "node tools/build.js && node tools/validate-privacy.js",
+    "build": "node tools/build.js && node tools/validate-privacy.js && npm run validate",
     "dev": "node tools/dev.js",
+    "validate": "node tools/validate-locales.js",
+    "test": "npm run build",
     "vercel-build": "npm run build"
   },
   "dependencies": {
diff --git a/tools/validate-locales.js b/tools/validate-locales.js
new file mode 100644
index 0000000..7fd0815
--- /dev/null
+++ b/tools/validate-locales.js
@@ -0,0 +1,182 @@
+import fs from "node:fs";
+import path from "node:path";
+
+const ROOT = process.cwd();
+const DOCS = path.join(ROOT, "docs");
+const DIST = path.join(ROOT, "dist");
+const LANGS = ["en", "pt", "es"];
+const GENERATED_PAGES = ["index.html", "docs.html", "terms.html", "privacy.html"];
+const REQUIRED_DOC_SECTIONS = [
+  "overview",
+  "item-1",
+  "item-1-1",
+  "item-1-2",
+  "item-1-3",
+  "item-1-4",
+  "item-1-5",
+  "item-1-6",
+  "item-2",
+  "item-3",
+  "item-3-1",
+];
+
+function read(file) {
+  return fs.readFileSync(file, "utf8");
+}
+
+function fail(message) {
+  throw new Error(message);
+}
+
+function extractIds(html) {
+  return new Set(
+    [...html.matchAll(/\bid=["']([^"']+)["']/gi)].map((match) => match[1]),
+  );
+}
+
+function assertNoUnresolvedPlaceholders(html, file) {
+  const unresolved = html.match(/\[\[[\w.]+\]\]|\{\{\{?[\w.:]+\}?\}\}?/g);
+  if (unresolved?.length) {
+    fail(
+      `Unresolved template placeholders in ${file}: ${[...new Set(unresolved)].join(", ")}`,
+    );
+  }
+}
+
+function resolveOutputPath(pathname) {
+  const normalized = pathname.replace(/\/+$/, "") || "/";
+  const routes = new Map([
+    ["/", "en/index.html"],
+    ["/docs", "en/docs.html"],
+    ["/404", "404.html"],
+  ]);
+
+  for (const lang of LANGS) {
+    routes.set(`/${lang}`, `${lang}/index.html`);
+    routes.set(`/${lang}/docs`, `${lang}/docs.html`);
+    routes.set(`/${lang}/terms`, `${lang}/terms.html`);
+    routes.set(`/${lang}/privacy`, `${lang}/privacy.html`);
+  }
+
+  const relativePath = routes.get(normalized) ?? normalized.replace(/^\//, "");
+  const outputPath = path.resolve(DIST, relativePath);
+
+  if (outputPath !== DIST && !outputPath.startsWith(`${DIST}${path.sep}`)) {
+    fail(`Internal route escapes the build output: ${pathname}`);
+  }
+
+  return outputPath;
+}
+
+function validateInternalLinks(html, sourcePath, publicPath) {
+  const baseUrl = new URL(publicPath, "https://musclelib.local");
+  const links = [...html.matchAll(/\bhref\s*=\s*(["'])(.*?)\1/gi)];
+
+  for (const match of links) {
+    const href = match[2].replace(/&/g, "&").trim();
+    if (!href) continue;
+
+    let target;
+    try {
+      target = new URL(href, baseUrl);
+    } catch {
+      fail(`Invalid link in ${sourcePath}: ${href}`);
+    }
+
+    if (target.protocol !== "http:" && target.protocol !== "https:") continue;
+    if (target.origin !== baseUrl.origin) continue;
+
+    const targetPath = resolveOutputPath(decodeURIComponent(target.pathname));
+    if (!fs.existsSync(targetPath) || !fs.statSync(targetPath).isFile()) {
+      fail(`Broken internal route in ${sourcePath}: ${href}`);
+    }
+
+    if (target.hash) {
+      const targetHtml = read(targetPath);
+      const targetIds = extractIds(targetHtml);
+      const fragment = decodeURIComponent(target.hash.slice(1));
+      if (!targetIds.has(fragment)) {
+        fail(`Broken internal anchor in ${sourcePath}: ${href}`);
+      }
+    }
+  }
+}
+
+const localeData = Object.fromEntries(
+  LANGS.map((lang) => {
+    const file = path.join(DOCS, "content", lang, "ui.json");
+    if (!fs.existsSync(file)) fail(`Missing locale file: ${file}`);
+
+    let data;
+    try {
+      data = JSON.parse(read(file));
+    } catch (error) {
+      fail(`Invalid JSON in ${file}: ${error.message}`);
+    }
+
+    for (const [key, value] of Object.entries(data)) {
+      if (typeof value !== "string" || value.trim() === "") {
+        fail(`Invalid or empty translation value in ${file}: ${key}`);
+      }
+    }
+
+    return [lang, data];
+  }),
+);
+
+const referenceKeys = new Set(Object.keys(localeData.en));
+for (const lang of LANGS.slice(1)) {
+  const keys = new Set(Object.keys(localeData[lang]));
+  const missing = [...referenceKeys].filter((key) => !keys.has(key));
+  const extra = [...keys].filter((key) => !referenceKeys.has(key));
+
+  if (missing.length || extra.length) {
+    fail(
+      `Locale key mismatch for ${lang}. Missing: ${missing.join(", ") || "none"}. Extra: ${extra.join(", ") || "none"}.`,
+    );
+  }
+}
+
+for (const lang of LANGS) {
+  for (const page of GENERATED_PAGES) {
+    const relativePath = `${lang}/${page}`;
+    const file = path.join(DIST, relativePath);
+    if (!fs.existsSync(file)) fail(`Missing generated page: ${relativePath}`);
+
+    const html = read(file);
+    const languageAttribute = new RegExp(
+      `<html\\b[^>]*\\blang=["']${lang}["']`,
+      "i",
+    );
+
+    if (!languageAttribute.test(html)) {
+      fail(`Invalid or missing lang attribute in ${relativePath}`);
+    }
+
+    assertNoUnresolvedPlaceholders(html, relativePath);
+    validateInternalLinks(html, relativePath, `/${lang}/${page}`);
+
+    if (page === "docs.html") {
+      const ids = extractIds(html);
+      const missingSections = REQUIRED_DOC_SECTIONS.filter((id) => !ids.has(id));
+      if (missingSections.length) {
+        fail(
+          `Missing required documentation sections in ${relativePath}: ${missingSections.join(", ")}`,
+        );
+      }
+    }
+  }
+}
+
+const notFoundPath = path.join(DIST, "404.html");
+if (!fs.existsSync(notFoundPath)) fail("Missing generated page: 404.html");
+const notFoundHtml = read(notFoundPath);
+if (!/<html\b[^>]*\blang=["']en["']/i.test(notFoundHtml)) {
+  fail("Invalid or missing lang attribute in 404.html");
+}
+assertNoUnresolvedPlaceholders(notFoundHtml, "404.html");
+validateInternalLinks(notFoundHtml, "404.html", "/404");
+
+console.log(
+  "Localization and generated-page checks passed for en, pt, and es.",
+);