diff --git a/dir-timestamp.js b/dir-timestamp.js
new file mode 100755
index 0000000..af12fa7
--- /dev/null
+++ b/dir-timestamp.js
@@ -0,0 +1,43 @@
+#!/usr/bin/env node
+
+import { readdirSync, statSync, utimesSync } from 'node:fs';
+
+if (process.argv.length < 3) {
+	console.log('Arguments: <directory>...');
+	process.exit(1);
+}
+
+function recurse(path) {
+	const stats = statSync(path);
+	if (stats.isFile()) {
+		return stats.mtimeMs;
+	}
+	if (stats.isDirectory()) {
+		let max = 0;
+		readdirSync(path).forEach(child => {
+			max = Math.max(max, recurse(path + '/' + child));
+		});
+		if (max === 0) {
+			throw new Error(`Empty directory: ${path}`);
+		}
+		utimesSync(path, max / 1000, max / 1000);
+		return max;
+	}
+	throw new Error(`Unexpected type: ${path}`);
+}
+
+let had_errors = false;
+
+for (const dir of process.argv.slice(2)) {
+	try {
+		recurse(dir.replace(/\/$/, ''));
+		console.log(`Done: ${dir}`);
+	} catch (err) {
+		console.log(`${err.message}\nAborting: ${dir}`);
+		had_errors = true;
+	}
+}
+
+if (had_errors) {
+	process.exit(1);
+}
diff --git a/package.json b/package.json
new file mode 100644
index 0000000..bedb411
--- /dev/null
+++ b/package.json
@@ -0,0 +1,3 @@
+{
+	"type": "module"
+}