diff --git a/cli/joomla_compat_check.php b/cli/joomla_compat_check.php
new file mode 100644
index 0000000..87c6d34
--- /dev/null
+++ b/cli/joomla_compat_check.php
@@ -0,0 +1,136 @@
+#!/usr/bin/env php
+<?php
+/* Copyright (C) 2026 Moko Consulting <hello@mokoconsulting.tech>
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ *
+ * FILE INFORMATION
+ * DEFGROUP: moko-platform.CLI
+ * INGROUP: moko-platform
+ * REPO: https://git.mokoconsulting.tech/MokoConsulting/moko-platform
+ * PATH: /cli/joomla_compat_check.php
+ * BRIEF: Check if extension targetplatform regex matches the latest Joomla version
+ *
+ * Usage:
+ *   php joomla_compat_check.php --path /repo
+ *   php joomla_compat_check.php --path /repo --github-output
+ *
+ * Options:
+ *   --path           Repository root (default: .)
+ *   --github-output  Export results to $GITHUB_OUTPUT
+ */
+
+declare(strict_types=1);
+
+$path = '.';
+$ghOutput = false;
+
+foreach ($argv as $i => $arg) {
+	if ($arg === '--path' && isset($argv[$i + 1])) $path = $argv[$i + 1];
+	if ($arg === '--github-output') $ghOutput = true;
+}
+
+$root = realpath($path) ?: $path;
+
+// ── Find manifest and extract targetplatform ────────────────────────────
+$manifest = null;
+$searchDirs = ["{$root}/src", $root];
+foreach ($searchDirs as $dir) {
+	if (!is_dir($dir)) continue;
+	foreach (glob("{$dir}/*.xml") ?: [] as $f) {
+		$xml = file_get_contents($f);
+		if (strpos($xml, '<extension') !== false && strpos($xml, 'targetplatform') !== false) {
+			$manifest = $f;
+			break 2;
+		}
+	}
+}
+
+if ($manifest === null) {
+	fwrite(STDERR, "No manifest with targetplatform found\n");
+	exit(1);
+}
+
+$xml = file_get_contents($manifest);
+$relManifest = str_replace($root . '/', '', $manifest);
+
+// Extract targetplatform version regex
+$targetRegex = '';
+if (preg_match('/targetplatform[^>]*version="([^"]+)"/', $xml, $m)) {
+	$targetRegex = $m[1];
+}
+
+if (empty($targetRegex)) {
+	echo "No targetplatform version found in {$relManifest}\n";
+	exit(1);
+}
+
+echo "Manifest:        {$relManifest}\n";
+echo "Target regex:    {$targetRegex}\n";
+
+// ── Fetch latest Joomla version ─────────────────────────────────────────
+$joomlaVersions = [];
+$updateUrl = 'https://update.joomla.org/core/sts/list_sts.xml';
+$updateXml = @file_get_contents($updateUrl);
+
+if ($updateXml === false) {
+	// Fallback: try the LTS feed
+	$updateUrl = 'https://update.joomla.org/core/list.xml';
+	$updateXml = @file_get_contents($updateUrl);
+}
+
+if ($updateXml !== false) {
+	// Parse all version entries
+	preg_match_all('/<version>([^<]+)<\/version>/', $updateXml, $matches);
+	$joomlaVersions = $matches[1] ?? [];
+}
+
+if (empty($joomlaVersions)) {
+	echo "WARNING: Could not fetch Joomla versions from update server\n";
+	echo "Tested URL: {$updateUrl}\n";
+	exit(0);
+}
+
+// Sort and get latest
+usort($joomlaVersions, 'version_compare');
+$latestJoomla = end($joomlaVersions);
+
+echo "Latest Joomla:   {$latestJoomla}\n";
+
+// ── Test compatibility ──────────────────────────────────────────────────
+// The targetplatform regex uses Joomla's regex format
+// Common patterns: "5\.[0-9]+" or "((5.[0-9])|(6.[0-9]))"
+$compatible = @preg_match("/{$targetRegex}/", $latestJoomla);
+
+if ($compatible === false) {
+	echo "ERROR: Invalid regex in targetplatform: {$targetRegex}\n";
+	$result = 'error';
+} elseif ($compatible === 1) {
+	echo "PASS: Joomla {$latestJoomla} matches targetplatform regex\n";
+	$result = 'pass';
+} else {
+	// Check which major versions are supported
+	$supported = [];
+	foreach (['5.0', '5.1', '5.2', '5.3', '5.4', '6.0', '6.1', '6.2', '7.0'] as $v) {
+		if (@preg_match("/{$targetRegex}/", $v)) {
+			$supported[] = $v;
+		}
+	}
+
+	echo "WARN: Joomla {$latestJoomla} does NOT match targetplatform regex\n";
+	echo "Supported versions: " . implode(', ', $supported) . "\n";
+	echo "Consider updating targetplatform to include Joomla {$latestJoomla}\n";
+	$result = 'warn';
+}
+
+// ── Export ───────────────────────────────────────────────────────────────
+if ($ghOutput) {
+	$ghFile = getenv('GITHUB_OUTPUT');
+	if ($ghFile) {
+		file_put_contents($ghFile, "compat_result={$result}\n", FILE_APPEND);
+		file_put_contents($ghFile, "compat_joomla={$latestJoomla}\n", FILE_APPEND);
+		file_put_contents($ghFile, "compat_regex={$targetRegex}\n", FILE_APPEND);
+	}
+}
+
+exit($result === 'error' ? 1 : 0);