diff --git a/.changeset/big-masks-care.md b/.changeset/big-masks-care.md
new file mode 100644
index 00000000000..8b3a17254e6
--- /dev/null
+++ b/.changeset/big-masks-care.md
@@ -0,0 +1,5 @@
+---
+"@effect/doctest": patch
+---
+
+Support `.mdx` files
diff --git a/packages/tools/doctest/README.md b/packages/tools/doctest/README.md
index e4d75e3383c..ad90bafd39a 100644
--- a/packages/tools/doctest/README.md
+++ b/packages/tools/doctest/README.md
@@ -1,6 +1,6 @@
 # `@effect/doctest`
 
-`@effect/doctest` extracts marked TypeScript examples from JSDoc comments and Markdown files, then runs each example as an isolated Vitest module.
+`@effect/doctest` extracts marked TypeScript examples from JSDoc comments, Markdown, and MDX files, then runs each example as an isolated Vitest module.
 
 Mark runnable fences with `import.meta.vitest`:
 
@@ -51,7 +51,7 @@ export const value = 1
 
 Markers must trail a complete expression statement or supported `const` declaration on the same line. Standalone markers, destructuring declarations, multiple declarations, and `let` or `var` declarations are not supported. The transform does not implicitly await promises, run Effects, or consume iterators; write those operations explicitly. Ordinary comments are ignored. Await asynchronous work so all assertions and cleanup occur before the snippet module finishes evaluating.
 
-Regular tests can use `include` in the same project. Documentation sources use `includeSource`, which lets Vitest discard files without the marker before collection. The plugin resolves imports relative to each example's original TypeScript or Markdown file:
+Regular tests can use `include` in the same project. Documentation sources use `includeSource`, which lets Vitest discard files without the marker before collection. The plugin resolves imports relative to each example's original TypeScript, Markdown, or MDX file:
 
 ```ts
 import * as Doctest from "@effect/doctest/Plugin"
@@ -61,7 +61,7 @@ export default defineConfig({
   plugins: [Doctest.plugin()],
   test: {
     include: ["test/**/*.test.ts"],
-    includeSource: ["src/**/*.ts", "docs/**/*.md"]
+    includeSource: ["src/**/*.ts", "docs/**/*.{md,mdx}"]
   }
 })
 ```
diff --git a/packages/tools/doctest/src/Source.ts b/packages/tools/doctest/src/Source.ts
index 2c8e2b33f86..9185b2ed5a4 100644
--- a/packages/tools/doctest/src/Source.ts
+++ b/packages/tools/doctest/src/Source.ts
@@ -98,4 +98,6 @@ export const extract = (source: string, format: SourceFormat = "jsdoc"): Readonl
  * @since 4.0.0
  */
 export const extractFile = (file: string): Promise<ReadonlyArray<Snippet>> =>
-  readFile(file, "utf8").then((source) => extract(source, file.endsWith(".md") ? "markdown" : "jsdoc"))
+  readFile(file, "utf8").then((source) =>
+    extract(source, file.endsWith(".md") || file.endsWith(".mdx") ? "markdown" : "jsdoc")
+  )
diff --git a/packages/tools/doctest/test/Source.test.ts b/packages/tools/doctest/test/Source.test.ts
index 18f108a212c..57508e6ec8a 100644
--- a/packages/tools/doctest/test/Source.test.ts
+++ b/packages/tools/doctest/test/Source.test.ts
@@ -116,4 +116,24 @@ describe("Source", () => {
       ])
     })
   })
+
+  describe("MDX", () => {
+    it("extracts marked TypeScript fences from mdx content", () => {
+      const source = [
+        "import { SomeComponent } from './component'",
+        "",
+        "## Example",
+        "",
+        "<SomeComponent />",
+        "",
+        "```ts import.meta.vitest",
+        "const result = 42",
+        "```"
+      ].join("\n")
+
+      assert.deepStrictEqual(Source.extract(source, "markdown"), [
+        { source: "const result = 42", line: 7, name: undefined }
+      ])
+    })
+  })
 })