diff --git a/.idx/dev.nix b/.idx/dev.nix
new file mode 100644
index 0000000000..20db14f6a0
--- /dev/null
+++ b/.idx/dev.nix
@@ -0,0 +1,50 @@
+# To learn more about how to use Nix to configure your environment
+# see: https://developers.google.com/idx/guides/customize-idx-env
+{ pkgs, ... }: {
+  # Which nixpkgs channel to use.
+  channel = "stable-24.05"; # or "unstable"
+
+  # Use https://search.nixos.org/packages to find packages
+  packages = [
+    pkgs.nodejs_22
+    pkgs.nodePackages.pnpm
+  ];
+
+  # Sets environment variables in the workspace
+  env = {};
+  idx = {
+    # Search for the extensions you want on https://open-vsx.org/ and use "publisher.id"
+    extensions = [
+      # "vscodevim.vim"
+    ];
+
+    # Enable previews
+    previews = {
+      enable = true;
+      previews = {
+        web = {
+          command = ["./dash_site" "serve"];
+          manager = "web";
+          env = {
+            # Environment variables to set for your server
+            PORT = "$PORT";
+          };
+        };
+      };
+    };
+
+    # Workspace lifecycle hooks
+    workspace = {
+      # Runs when a workspace is first created
+      onCreate = {
+        get-submodule = "git submodule update --init --recursive";
+        pnpm-install = "pnpm install";
+      };
+      # Runs when the workspace is (re)started
+      onStart = {
+        # Example: start a background task to watch and re-build backend code
+        # watch-backend = "npm run watch-backend";
+      };
+    };
+  };
+}
diff --git a/README.md b/README.md
index 836120532a..8eadeeca2a 100644
--- a/README.md
+++ b/README.md
@@ -3,6 +3,21 @@
 [![Build Status SVG][]][Repo on GitHub Actions]
 [![OpenSSF Scorecard SVG][]][Scorecard Results]
 
+<a href="https://idx.google.com/import?url=https%3A%2F%2Fgithub.com%2Fdart-lang%2Fsite-www">
+  <picture>
+    <source
+      media="(prefers-color-scheme: dark)"
+      srcset="https://cdn.idx.dev/btn/open_dark_32.svg">
+    <source
+      media="(prefers-color-scheme: light)"
+      srcset="https://cdn.idx.dev/btn/open_light_32.svg">
+    <img
+      height="32"
+      alt="Open in IDX"
+      src="https://cdn.idx.dev/btn/open_purple_32.svg">
+  </picture>
+</a>
+
 The documentation site for the [Dart programming language](https://dart.dev), 
 built with [Eleventy][] and hosted on [Firebase][].
 
diff --git a/tool/dart_site/lib/src/commands/serve.dart b/tool/dart_site/lib/src/commands/serve.dart
index 8d73041728..80c68b7e35 100644
--- a/tool/dart_site/lib/src/commands/serve.dart
+++ b/tool/dart_site/lib/src/commands/serve.dart
@@ -13,7 +13,12 @@ final class ServeSiteCommand extends Command<int> {
   Future<int> run() async {
     final process = await Process.start(
       'npx',
-      const ['eleventy', '--serve', '--incremental'],
+      [
+        'eleventy',
+        '--serve',
+        '--incremental',
+        '--port=${Platform.environment['PORT'] ?? 4000}'
+      ],
       environment: const {
         'PRODUCTION': 'false',
       },