diff --git a/content/alarm-clock/Clock.cpp b/content/alarm-clock/Clock.cpp
index fdef219..ab2a12e 100644
--- a/content/alarm-clock/Clock.cpp
+++ b/content/alarm-clock/Clock.cpp
@@ -20,7 +20,7 @@
    since this number is out of the range for `int`
    (-32,768 ... 32,767), we'll get an unexpected result:
    -5536 instead of 60000.
- */
+*/
 #define MINUTE 60 * 1000L /* ms */
 #define TIMESPAN_DAY TimeSpan(1, 0, 0, 0)
 /* gac:end */
diff --git a/content/dice-roller/dice-roller.ino b/content/dice-roller/dice-roller.ino
index 0e31ab8..6b52892 100644
--- a/content/dice-roller/dice-roller.ino
+++ b/content/dice-roller/dice-roller.ino
@@ -49,8 +49,8 @@ void loop() {
      ✅ Give `digitalRead(...)` a meaningful name by storing the result
      it into a variable */
   bool buttonPressed = digitalRead(BUTTON_PIN) == LOW;
-   /* gac:
-      Check if this is the first time the button is pressed. */
+  /* gac:
+     Check if this is the first time the button is pressed. */
   if (!randomReady && buttonPressed) {
     /* Initialize the random number generator with the number of
        microseconds between program start and the first button press */
diff --git a/content/simon/pitches.h b/content/simon/pitches.h
index d12cfbd..c597c5a 100644
--- a/content/simon/pitches.h
+++ b/content/simon/pitches.h
@@ -1,6 +1,6 @@
 /**************************************************
- * This file defines constants with the frequency
- * of different musical notes.
+   This file defines constants with the frequency
+   of different musical notes.
  *************************************************/
 
 #define NOTE_B0  31
diff --git a/package-lock.json b/package-lock.json
index c177e6a..e321faa 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -4372,6 +4372,12 @@
       "integrity": "sha512-+Ryf6g3BKoRc7jfp7ad8tM4TtMiaWvbF/1/sQcZPkkS7ag3D5nMBCe2UfOTONtAkaG0tO0ij3C5Lwmf1EiyjHg==",
       "dev": true
     },
+    "astyle": {
+      "version": "2.0.0",
+      "resolved": "https://registry.npmjs.org/astyle/-/astyle-2.0.0.tgz",
+      "integrity": "sha512-qmtKy9S4k2xjHIQei6DjLtHy1I7Nu3dZFACFSMMHBypxn2UuH6M9VHwJ4/3WWtUmexs7j1cwfC2QhsGLmLyu8A==",
+      "dev": true
+    },
     "async-each": {
       "version": "1.0.3",
       "resolved": "https://registry.npmjs.org/async-each/-/async-each-1.0.3.tgz",
diff --git a/package.json b/package.json
index fba34f0..6a41eaa 100644
--- a/package.json
+++ b/package.json
@@ -34,6 +34,7 @@
     "@types/react-test-renderer": "^16.9.2",
     "@typescript-eslint/eslint-plugin": "^3.7.0",
     "@typescript-eslint/parser": "^3.7.0",
+    "astyle": "^2.0.0",
     "eslint": "^7.5.0",
     "eslint-config-prettier": "^6.11.0",
     "eslint-config-standard": "^14.1.1",
@@ -63,6 +64,9 @@
     ],
     "*.md": [
       "prettier --write"
+    ],
+    "*.{h,ino,cpp}": [
+      "node utils/format-arduino-code"
     ]
   }
 }
diff --git a/utils/format-arduino-code.js b/utils/format-arduino-code.js
new file mode 100644
index 0000000..ce7ecc9
--- /dev/null
+++ b/utils/format-arduino-code.js
@@ -0,0 +1,36 @@
+/**
+ * A small command-line utility used by the git pre-commit hook
+ * to automatically format the code.
+ */
+
+const { format } = require('astyle');
+const { promises: fs } = require('fs');
+
+// Source: https://github.com/arduino/Arduino/blob/ide-1.5.x/build/shared/lib/formatter.conf
+const ARDUINO_FORMAT_RULES = [
+  'mode=c',
+  'indent=spaces=2',
+  'indent-preprocessor',
+  'indent-classes',
+  'indent-switches',
+  'indent-cases',
+  'indent-col1-comments',
+  'pad-oper',
+  'pad-header',
+  'keep-one-line-statements',
+  'remove-comment-prefix',
+].join(' ');
+
+async function main() {
+  for (const file of process.argv.slice(2)) {
+    const source = await fs.readFile(file, 'utf-8');
+    console.log(file);
+    const formatted = await format(source, ARDUINO_FORMAT_RULES);
+    if (source !== formatted) {
+      console.log(`* Formating ${file}`);
+      await fs.writeFile(file, formatted);
+    }
+  }
+}
+
+main();