diff --git a/__tests__/mdx-lint.spec.ts b/__tests__/mdx-lint.spec.ts
new file mode 100644
index 0000000..7374cc9
--- /dev/null
+++ b/__tests__/mdx-lint.spec.ts
@@ -0,0 +1,129 @@
+import { spawnSync } from "child_process";
+import { mkdtempSync, readFileSync, rmSync, writeFileSync } from "fs";
+import { tmpdir } from "os";
+import * as path from "path";
+import lintWorker from "../src/utils/lint-worker";
+
+const CLI = path.resolve(__dirname, "../lib/src/lint-md.js");
+const RULES = { "space-around-alphabet": 2 };
+const MDX = [
+  'import Widget from "中文English";',
+  "",
+  'export const title = "中文English";',
+  "",
+  '<Widget label="中文English" count={"中文English"} />',
+  "",
+  '{"中文English"}',
+  "",
+  "<Widget>正文English内容。</Widget>",
+  "",
+].join("\n");
+
+describe("MDX lint", () => {
+  let tmpDir: string;
+  let configPath: string;
+
+  beforeEach(() => {
+    tmpDir = mkdtempSync(path.join(tmpdir(), "lint-md-mdx-"));
+    configPath = path.join(tmpDir, ".lintmdrc");
+    writeFileSync(configPath, JSON.stringify({ rules: RULES }), "utf8");
+  });
+
+  afterEach(() => {
+    rmSync(tmpDir, { recursive: true, force: true });
+  });
+
+  test("lints Markdown text", async () => {
+    const filePath = path.join(tmpDir, "document.md");
+    writeFileSync(filePath, "正文English内容。\n", "utf8");
+
+    const result = await lintWorker({
+      filePath,
+      rules: RULES,
+      isFixMode: false,
+    });
+
+    expect(result.diagnostics).toHaveLength(2);
+    expect(
+      result.diagnostics.map(({ ruleId, line }) => [ruleId, line])
+    ).toEqual([
+      ["space-around-alphabet", 1],
+      ["space-around-alphabet", 1],
+    ]);
+  });
+
+  test.each([".mdx", ".MDX"])(
+    "lints %s through the CLI and skips JSX, ESM, and expressions",
+    (extension) => {
+      const filePath = path.join(tmpDir, `document${extension}`);
+      writeFileSync(filePath, MDX, "utf8");
+
+      const result = spawnSync(
+        process.execPath,
+        [CLI, filePath, "--config", configPath],
+        { encoding: "utf8" }
+      );
+
+      expect(result.error).toBeUndefined();
+      expect(result.status).toBe(1);
+      expect(result.stdout).toContain(filePath);
+      expect(result.stdout).toContain("9:10");
+      expect(result.stdout).toContain("9:17");
+      expect(result.stdout).toContain("2 problems");
+    }
+  );
+
+  test("routes Markdown and MDX through the CLI", () => {
+    const markdownPath = path.join(tmpDir, "document.md");
+    const mdxPath = path.join(tmpDir, "document.mdx");
+    writeFileSync(markdownPath, "正文English内容。\n", "utf8");
+    writeFileSync(mdxPath, MDX, "utf8");
+
+    const result = spawnSync(
+      process.execPath,
+      [CLI, markdownPath, mdxPath, "--config", configPath],
+      { encoding: "utf8" }
+    );
+
+    expect(result.error).toBeUndefined();
+    expect(result.status).toBe(1);
+    expect(result.stdout).toContain(markdownPath);
+    expect(result.stdout).toContain(mdxPath);
+    expect(result.stdout).toContain("4 problems");
+  });
+
+  test("rejects a direct worker fix request for MDX", async () => {
+    const filePath = path.join(tmpDir, "document.mdx");
+    writeFileSync(filePath, MDX, "utf8");
+
+    await expect(
+      lintWorker({ filePath, rules: RULES, isFixMode: true })
+    ).rejects.toThrow("--fix does not support .mdx files");
+    expect(readFileSync(filePath, "utf8")).toBe(MDX);
+  });
+
+  test.each([".mdx", ".MDX"])(
+    "rejects %s fix requests before changing any file",
+    (extension) => {
+      const markdownPath = path.join(tmpDir, "document.md");
+      const mdxPath = path.join(tmpDir, `document${extension}`);
+      const markdown = "正文English内容。\n";
+      writeFileSync(markdownPath, markdown, "utf8");
+      writeFileSync(mdxPath, MDX, "utf8");
+
+      const result = spawnSync(
+        process.execPath,
+        [CLI, markdownPath, mdxPath, "--fix", "--config", configPath],
+        { encoding: "utf8" }
+      );
+
+      expect(result.error).toBeUndefined();
+      expect(result.status).toBe(1);
+      expect(result.stderr).toContain(
+        "--fix does not support .mdx files. No files were changed."
+      );
+      expect(readFileSync(markdownPath, "utf8")).toBe(markdown);
+      expect(readFileSync(mdxPath, "utf8")).toBe(MDX);
+    }
+  );
+});
diff --git a/package.json b/package.json
index bf5f697..87b9313 100644
--- a/package.json
+++ b/package.json
@@ -54,7 +54,7 @@
     ]
   },
   "dependencies": {
-    "@lint-md/core": "^2.5.2",
+    "@lint-md/core": "^2.6.0",
     "chalk": "^4",
     "commander": "^9.4.1",
     "glob": "^13.0.6",
diff --git a/scripts/test-package.mjs b/scripts/test-package.mjs
index b4790ce..7044cef 100644
--- a/scripts/test-package.mjs
+++ b/scripts/test-package.mjs
@@ -87,14 +87,17 @@ try {
 
   const fixtureDirectory = join(temporaryDirectory, "fixtures");
   const cleanFile = join(fixtureDirectory, "clean.md");
+  const cleanMdxFile = join(fixtureDirectory, "clean.mdx");
   const fixableFile = join(fixtureDirectory, "fixable.md");
   mkdirSync(fixtureDirectory);
   cpSync(join(projectRoot, "examples", "space-around.md"), fixableFile, {
     recursive: false,
   });
   writeFileSync(cleanFile, cleanMarkdown, "utf8");
+  writeFileSync(cleanMdxFile, '# Hello\n\n<Card label="text" />\n', "utf8");
 
   run(lintMd, [cleanFile]);
+  run(lintMd, [cleanMdxFile]);
   const originalFixableContent = readFileSync(fixableFile, "utf8");
   run(lintMd, [fixableFile, "--fix"]);
   const fixedContent = readFileSync(fixableFile, "utf8");
diff --git a/src/utils/lint-worker.ts b/src/utils/lint-worker.ts
index 28907a7..6ab1205 100644
--- a/src/utils/lint-worker.ts
+++ b/src/utils/lint-worker.ts
@@ -1,15 +1,29 @@
 import { readFile } from "fs/promises";
+import { extname } from "path";
 import { fixMarkdown, lintMarkdown } from "@lint-md/core";
+import type { LintMdResult } from "@lint-md/core";
 import type { LintWorkerOptions } from "../types";
 import { toBatchLintItem } from "./to-batch-lint-item";
 
 const lintWorker = async (options: LintWorkerOptions) => {
   const { filePath, rules, isFixMode } = options;
+  const isMdx = extname(filePath).toLowerCase() === ".mdx";
+
+  if (isMdx && isFixMode) {
+    throw new Error("--fix does not support .mdx files");
+  }
 
   const content = await readFile(filePath, "utf8");
-  const result = isFixMode
-    ? fixMarkdown(content, { rules })
-    : lintMarkdown(content, { rules: rules ?? {} });
+  let result: LintMdResult;
+  if (isMdx) {
+    const { lintMdx } =
+      require("@lint-md/core/mdx") as typeof import("@lint-md/core/mdx");
+    result = lintMdx(content, { rules: rules ?? {} });
+  } else {
+    result = isFixMode
+      ? fixMarkdown(content, { rules })
+      : lintMarkdown(content, { rules: rules ?? {} });
+  }
 
   // Core returns fixedResult even when no rule changed the text. Compare with
   // the content we already read so the main thread writes only real changes.
diff --git a/src/utils/load-md-files.ts b/src/utils/load-md-files.ts
index 990bb81..c2a245c 100644
--- a/src/utils/load-md-files.ts
+++ b/src/utils/load-md-files.ts
@@ -25,7 +25,13 @@ export const loadMdFiles = async (
   for (const entry of entries) {
     if (entry.isSymbolicLink()) continue;
     const fullPath = entry.fullpath();
-    if (extensions.some((ext) => fullPath.endsWith(ext))) files.add(fullPath);
+    if (
+      extensions.some((ext) =>
+        fullPath.toLowerCase().endsWith(ext.toLowerCase())
+      )
+    ) {
+      files.add(fullPath);
+    }
   }
 
   // Sort so lint report order stays stable across OS, filesystem, and