diff --git a/demo/broken.html b/demo/broken.html
index d39825b..ed1fc70 100644
--- a/demo/broken.html
+++ b/demo/broken.html
@@ -4,7 +4,7 @@
     <title>Broken Page</title>
 </head>
 <body>
-    <h1>Welcome to a broken page</h1>
+    <h1 id="main-content">Welcome to a broken page</h1>
     
     <!-- Missing alt attribute -->
     <img src="logo.png">
@@ -15,6 +15,21 @@
     <!-- Empty button -->
     <button type="submit"></button>
     
+    <!-- Positive tabindex -->
+    <a href="/keyboard" tabindex="5">Keyboard test</a>
+
+    <!-- Duplicate ID -->
+    <div id="main-content">This is a duplicate main-content ID div!</div>
+
+    <!-- Low Contrast -->
+    <p style="color: #888888; background-color: #999999;">This text has extremely low contrast ratio!</p>
+
+    <!-- Invalid ARIA role and missing controls target -->
+    <div role="cool-widget" aria-controls="non-existent-popup">WAI-ARIA elements</div>
+
+    <!-- Missing Iframe Title -->
+    <iframe src="https://www.youtube.com/embed/dQw4w9WgXcQ" width="560" height="315"></iframe>
+
     <p>This page has multiple accessibility issues.</p>
 </body>
 </html>
diff --git a/src/Rules/AriaRole.php b/src/Rules/AriaRole.php
new file mode 100644
index 0000000..40b2110
--- /dev/null
+++ b/src/Rules/AriaRole.php
@@ -0,0 +1,76 @@
+<?php
+
+namespace YakNet\AccessibilityConsole\Rules;
+
+use YakNet\AccessibilityConsole\Core\AbstractRule;
+use YakNet\AccessibilityConsole\Core\Severity;
+use YakNet\AccessibilityConsole\Core\WCAGStandard;
+
+class AriaRole extends AbstractRule
+{
+    private static array $validRoles = [
+        'alert', 'alertdialog', 'application', 'article', 'banner', 'button', 'cell', 'checkbox',
+        'columnheader', 'combobox', 'complementary', 'contentinfo', 'definition', 'dialog', 'directory',
+        'document', 'feed', 'figure', 'form', 'grid', 'gridcell', 'group', 'heading', 'img', 'link',
+        'list', 'listbox', 'listitem', 'log', 'main', 'marquee', 'math', 'menu', 'menubar', 'menuitem',
+        'menuitemcheckbox', 'menuitemradio', 'navigation', 'none', 'note', 'option', 'presentation',
+        'progressbar', 'radio', 'radiogroup', 'region', 'row', 'rowgroup', 'rowheader', 'scrollbar',
+        'search', 'searchbox', 'separator', 'slider', 'spinbutton', 'status', 'switch', 'tab', 'table',
+        'tablist', 'tabpanel', 'term', 'textbox', 'timer', 'toolbar', 'tooltip', 'tree', 'treegrid',
+        'treeitem'
+    ];
+
+    public function check(\DOMDocument $doc): array
+    {
+        $violations = [];
+        $xpath = new \DOMXPath($doc);
+        
+        // 1. Check WAI-ARIA Role Validity
+        $roleElements = $xpath->query('//*[@role]');
+        foreach ($roleElements as $el) {
+            if (!$el instanceof \DOMElement) {
+                continue;
+            }
+            $role = trim($el->getAttribute('role'));
+            if ($role === '') {
+                continue;
+            }
+            $roles = array_filter(explode(' ', $role));
+            foreach ($roles as $r) {
+                if (!in_array(strtolower($r), self::$validRoles, true)) {
+                    $violations[] = $this->createViolation(
+                        "Invalid ARIA role \"{$r}\" declared on element. Must use standard WAI-ARIA roles.",
+                        $el
+                    );
+                }
+            }
+        }
+
+        // 2. Check aria-controls Targets Existence
+        $controlsElements = $xpath->query('//*[@aria-controls]');
+        foreach ($controlsElements as $el) {
+            if (!$el instanceof \DOMElement) {
+                continue;
+            }
+            $targetsStr = trim($el->getAttribute('aria-controls'));
+            if ($targetsStr === '') {
+                continue;
+            }
+            $targets = array_filter(explode(' ', $targetsStr));
+            foreach ($targets as $targetId) {
+                $targetQuery = $xpath->query('//*[@id="' . $targetId . '"]');
+                if ($targetQuery->length === 0) {
+                    $violations[] = $this->createViolation(
+                        "Attribute aria-controls=\"{$targetId}\" targets an element that does not exist in the document.",
+                        $el
+                    );
+                }
+            }
+        }
+
+        return $violations;
+    }
+
+    public function getStandard(): WCAGStandard { return WCAGStandard::A; }
+    public function getSeverity(): Severity { return Severity::ERROR; }
+}
diff --git a/src/Rules/ColorContrast.php b/src/Rules/ColorContrast.php
new file mode 100644
index 0000000..008b95b
--- /dev/null
+++ b/src/Rules/ColorContrast.php
@@ -0,0 +1,124 @@
+<?php
+
+namespace YakNet\AccessibilityConsole\Rules;
+
+use DOMElement;
+use YakNet\AccessibilityConsole\Core\Severity;
+use YakNet\AccessibilityConsole\Core\Violation;
+use YakNet\AccessibilityConsole\Core\WCAGStandard;
+
+class ColorContrast extends AbstractRule
+{
+    public function getId(): string { return 'WCAG_1_4_3_CONTRAST'; }
+    public function getDescription(): string { return 'Text must have sufficient contrast against the background (4.5:1 minimum).'; }
+    public function getStandard(): WCAGStandard { return WCAGStandard::AA; }
+    public function getSeverity(): Severity { return Severity::WARNING; }
+
+    public function check(DOMElement $element): ?Violation
+    {
+        if (!$element->hasAttribute('style')) {
+            return null;
+        }
+
+        $style = $element->getAttribute('style');
+        
+        $color = $this->parseColorValue($style, 'color');
+        $bg = $this->parseColorValue($style, 'background-color') ?: $this->parseColorValue($style, 'background');
+
+        if ($color === null || $bg === null) {
+            return null;
+        }
+
+        $cRGB = $this->hexToRgb($color);
+        $bgRGB = $this->hexToRgb($bg);
+
+        if ($cRGB === null || $bgRGB === null) {
+            return null;
+        }
+
+        $cLum = $this->getLuminance($cRGB[0], $cRGB[1], $cRGB[2]);
+        $bgLum = $this->getLuminance($bgRGB[0], $bgRGB[1], $bgRGB[2]);
+
+        $ratio = ($cLum > $bgLum) ? ($cLum + 0.05) / ($bgLum + 0.05) : ($bgLum + 0.05) / ($cLum + 0.05);
+
+        $isLarge = false;
+        if (preg_match('/font-size\s*:\s*([0-9.]+)(px|em|rem|pt)/i', $style, $matches)) {
+            $val = (float)$matches[1];
+            $unit = strtolower($matches[2]);
+            if (($unit === 'px' && $val >= 24) || ($unit === 'pt' && $val >= 18) || (($unit === 'em' || $unit === 'rem') && $val >= 1.5)) {
+                $isLarge = true;
+            }
+        }
+        if (preg_match('/font-weight\s*:\s*(bold|[7-9]00)/i', $style)) {
+            if (preg_match('/font-size\s*:\s*([0-9.]+)(px|em|rem|pt)/i', $style, $matches)) {
+                $val = (float)$matches[1];
+                $unit = strtolower($matches[2]);
+                if (($unit === 'px' && $val >= 18) || ($unit === 'pt' && $val >= 14) || (($unit === 'em' || $unit === 'rem') && $val >= 1.2)) {
+                    $isLarge = true;
+                }
+            }
+        }
+
+        $minRatio = $isLarge ? 3.0 : 4.5;
+
+        if ($ratio < $minRatio) {
+            $formattedRatio = round($ratio, 2);
+            return $this->createViolation(
+                $element,
+                "Insufficient contrast ratio of {$formattedRatio}:1. Minimum required is {$minRatio}:1.",
+                "Adjust colors to increase contrast. For example, text: {$color}, background: {$bg}."
+            );
+        }
+
+        return null;
+    }
+
+    private function parseColorValue(string $style, string $property): ?string
+    {
+        if (preg_match('/(?:^|;)\s*' . preg_quote($property, '/') . '\s*:\s*([^;]+)/i', $style, $matches)) {
+            $value = trim($matches[1]);
+            if (preg_match('/^#([0-9a-f]{3,6})$/i', $value)) {
+                return $value;
+            }
+            $colors = [
+                'black' => '#000000', 'white' => '#ffffff', 'red' => '#ff0000',
+                'green' => '#008000', 'blue' => '#0000ff', 'yellow' => '#ffff00',
+                'gray' => '#808080', 'grey' => '#808080', 'silver' => '#c0c0c0',
+            ];
+            if (isset($colors[strtolower($value)])) {
+                return $colors[strtolower($value)];
+            }
+        }
+        return null;
+    }
+
+    private function hexToRgb(string $hex): ?array
+    {
+        $hex = ltrim($hex, '#');
+        if (strlen($hex) === 3) {
+            $r = hexdec(substr($hex, 0, 1) . substr($hex, 0, 1));
+            $g = hexdec(substr($hex, 1, 1) . substr($hex, 1, 1));
+            $b = hexdec(substr($hex, 2, 1) . substr($hex, 2, 1));
+            return [$r, $g, $b];
+        } elseif (strlen($hex) === 6) {
+            $r = hexdec(substr($hex, 0, 2));
+            $g = hexdec(substr($hex, 2, 2));
+            $b = hexdec(substr($hex, 4, 2));
+            return [$r, $g, $b];
+        }
+        return null;
+    }
+
+    private function getLuminance(float $r, float $g, float $b): float
+    {
+        $rs = $r / 255.0;
+        $gs = $g / 255.0;
+        $bs = $b / 255.0;
+
+        $rVal = ($rs <= 0.03928) ? $rs / 12.92 : pow(($rs + 0.055) / 1.055, 2.4);
+        $gVal = ($gs <= 0.03928) ? $gs / 12.92 : pow(($gs + 0.055) / 1.055, 2.4);
+        $bVal = ($bs <= 0.03928) ? $bs / 12.92 : pow(($bs + 0.055) / 1.055, 2.4);
+
+        return 0.2126 * $rVal + 0.7152 * $gVal + 0.0722 * $bVal;
+    }
+}
diff --git a/src/Rules/DuplicateId.php b/src/Rules/DuplicateId.php
new file mode 100644
index 0000000..6c834f3
--- /dev/null
+++ b/src/Rules/DuplicateId.php
@@ -0,0 +1,48 @@
+<?php
+
+namespace YakNet\AccessibilityConsole\Rules;
+
+use YakNet\AccessibilityConsole\Core\AbstractRule;
+use YakNet\AccessibilityConsole\Core\Severity;
+use YakNet\AccessibilityConsole\Core\WCAGStandard;
+
+class DuplicateId extends AbstractRule
+{
+    public function check(\DOMDocument $doc): array
+    {
+        $violations = [];
+        $xpath = new \DOMXPath($doc);
+        $elements = $xpath->query('//*[@id]');
+        
+        $ids = [];
+        foreach ($elements as $el) {
+            if (!$el instanceof \DOMElement) {
+                continue;
+            }
+            $id = $el->getAttribute('id');
+            if ($id === '') {
+                continue;
+            }
+            if (!isset($ids[$id])) {
+                $ids[$id] = [];
+            }
+            $ids[$id][] = $el;
+        }
+
+        foreach ($ids as $id => $elementsWithId) {
+            if (count($elementsWithId) > 1) {
+                foreach ($elementsWithId as $el) {
+                    $violations[] = $this->createViolation(
+                        "Duplicate ID \"{$id}\" found. Element ID attribute must be unique across the document.",
+                        $el
+                    );
+                }
+            }
+        }
+
+        return $violations;
+    }
+
+    public function getStandard(): WCAGStandard { return WCAGStandard::A; }
+    public function getSeverity(): Severity { return Severity::ERROR; }
+}
diff --git a/src/Rules/IframeTitle.php b/src/Rules/IframeTitle.php
new file mode 100644
index 0000000..548d24c
--- /dev/null
+++ b/src/Rules/IframeTitle.php
@@ -0,0 +1,33 @@
+<?php
+
+namespace YakNet\AccessibilityConsole\Rules;
+
+use DOMElement;
+use YakNet\AccessibilityConsole\Core\Severity;
+use YakNet\AccessibilityConsole\Core\Violation;
+use YakNet\AccessibilityConsole\Core\WCAGStandard;
+
+class IframeTitle extends AbstractRule
+{
+    public function getId(): string { return 'WCAG_4_1_2_IFRAME_TITLE'; }
+    public function getDescription(): string { return 'Iframe elements must have a non-empty title attribute to describe their content.'; }
+    public function getStandard(): WCAGStandard { return WCAGStandard::A; }
+    public function getSeverity(): Severity { return Severity::ERROR; }
+
+    public function check(DOMElement $element): ?Violation
+    {
+        if (strtolower($element->tagName) !== 'iframe') {
+            return null;
+        }
+
+        if (!$element->hasAttribute('title') || trim($element->getAttribute('title')) === '') {
+            return $this->createViolation(
+                $element,
+                "Iframe element is missing a descriptive title attribute.",
+                "Add a descriptive title attribute, e.g., title=\"Embedded Map\" or title=\"Video Player\"."
+            );
+        }
+
+        return null;
+    }
+}
diff --git a/src/Rules/StandardRuleSet.php b/src/Rules/StandardRuleSet.php
index 481e674..f663c68 100644
--- a/src/Rules/StandardRuleSet.php
+++ b/src/Rules/StandardRuleSet.php
@@ -18,6 +18,11 @@ class StandardRuleSet
             new FieldsetLegend(),
             new HeadingOrder(),
             new MetaViewport(),
+            new TabindexOrder(),
+            new ColorContrast(),
+            new DuplicateId(),
+            new AriaRole(),
+            new IframeTitle(),
         ];
     }
 }
diff --git a/src/Rules/TabindexOrder.php b/src/Rules/TabindexOrder.php
new file mode 100644
index 0000000..ff1142c
--- /dev/null
+++ b/src/Rules/TabindexOrder.php
@@ -0,0 +1,34 @@
+<?php
+
+namespace YakNet\AccessibilityConsole\Rules;
+
+use DOMElement;
+use YakNet\AccessibilityConsole\Core\Severity;
+use YakNet\AccessibilityConsole\Core\Violation;
+use YakNet\AccessibilityConsole\Core\WCAGStandard;
+
+class TabindexOrder extends AbstractRule
+{
+    public function getId(): string { return 'WCAG_2_4_3_TABINDEX'; }
+    public function getDescription(): string { return 'Avoid positive tabindex values to maintain natural keyboard focus order.'; }
+    public function getStandard(): WCAGStandard { return WCAGStandard::A; }
+    public function getSeverity(): Severity { return Severity::WARNING; }
+
+    public function check(DOMElement $element): ?Violation
+    {
+        if ($element->hasAttribute('tabindex')) {
+            $tabindex = $element->getAttribute('tabindex');
+            if (is_numeric($tabindex)) {
+                $val = (int)$tabindex;
+                if ($val > 0) {
+                    return $this->createViolation(
+                        $element,
+                        "Avoid positive tabindex values (tabindex=\"{$val}\") to preserve the natural tab order.",
+                        "Remove the positive tabindex or change it to \"0\" or \"-1\"."
+                    );
+                }
+            }
+        }
+        return null;
+    }
+}