diff --git a/src/Evaluator.php b/src/Evaluator.php
index f810894..fe98ed8 100644
--- a/src/Evaluator.php
+++ b/src/Evaluator.php
@@ -4,41 +4,99 @@ declare(strict_types=1);
 
 namespace FlagPole;
 
+use Psr\Log\LoggerInterface;
+use Psr\Log\NullLogger;
+
 final class Evaluator
 {
+    private LoggerInterface $logger;
+
+    public function __construct(?LoggerInterface $logger = null)
+    {
+        $this->logger = $logger ?? new NullLogger();
+    }
+
     public function evaluate(Flag $flag, ?Context $context = null, bool $default = false): bool
     {
         $context ??= new Context();
 
         // 1) Allow list wins if present
         if (!empty($flag->allowList)) {
-            $key = $this->resolveTargetingKey($context);
+            $key = $this->resolveTargetingKey($context, $flag->targetingKey);
             if ($key !== null && in_array((string)$key, $flag->allowList, true)) {
+                $this->logger->info(sprintf('Flag "%s" enabled for key "%s" via allowList.', $flag->name, $key));
                 return true;
             }
         }
 
         // 2) Explicit on/off
         if ($flag->enabled !== null) {
+            $this->logger->info(sprintf('Flag "%s" evaluated to %s via explicit "enabled" override.', $flag->name, $flag->enabled ? 'TRUE' : 'FALSE'));
             return $flag->enabled;
         }
 
-        // 3) Percentage rollout if available
+        // 3) Rules matching
+        if (!empty($flag->rules)) {
+            foreach ($flag->rules as $rule) {
+                if ($this->matchRule($rule, $context)) {
+                    $this->logger->info(sprintf('Flag "%s" enabled via rule (attribute: %s, operator: %s).', $flag->name, $rule->attribute, $rule->operator));
+                    return true;
+                }
+            }
+        }
+
+        // 4) Percentage rollout if available
         if ($flag->rolloutPercentage !== null) {
-            $key = $this->resolveTargetingKey($context);
+            $key = $this->resolveTargetingKey($context, $flag->targetingKey);
             if ($key === null) {
+                $this->logger->info(sprintf('Flag "%s" rollout evaluation failed: no targeting key found. Using default: %s.', $flag->name, $default ? 'TRUE' : 'FALSE'));
                 return $default;
             }
             $bucket = $this->computeBucket($flag->name, (string)$key);
-            return $bucket < $flag->rolloutPercentage;
+            $result = $bucket < $flag->rolloutPercentage;
+            $this->logger->info(sprintf(
+                'Flag "%s" evaluated to %s via rolloutPercentage (%d%%). Bucket: %d, Key: %s.',
+                $flag->name,
+                $result ? 'TRUE' : 'FALSE',
+                $flag->rolloutPercentage,
+                $bucket,
+                $key
+            ));
+            return $result;
         }
 
-        // 4) Fallback
+        // 5) Fallback
+        $this->logger->info(sprintf('Flag "%s" using fallback default: %s.', $flag->name, $default ? 'TRUE' : 'FALSE'));
         return $default;
     }
 
-    private function resolveTargetingKey(Context $context): ?string
+    private function matchRule(Rule $rule, Context $context): bool
     {
+        $attributeValue = $context->get($rule->attribute);
+
+        return match ($rule->operator) {
+            'eq' => $attributeValue === $rule->value,
+            'neq' => $attributeValue !== $rule->value,
+            'gt' => $attributeValue > $rule->value,
+            'gte' => $attributeValue >= $rule->value,
+            'lt' => $attributeValue < $rule->value,
+            'lte' => $attributeValue <= $rule->value,
+            'in' => is_array($rule->value) && in_array($attributeValue, $rule->value, true),
+            'nin' => is_array($rule->value) && !in_array($attributeValue, $rule->value, true),
+            'contains' => is_string($attributeValue) && is_string($rule->value) && str_contains($attributeValue, $rule->value),
+            default => throw new \LogicException(sprintf('Unsupported operator "%s" encountered during evaluation.', $rule->operator)),
+        };
+    }
+
+    private function resolveTargetingKey(Context $context, ?string $preferredKey = null): ?string
+    {
+        if ($preferredKey !== null) {
+            $v = $context->get($preferredKey);
+            if ($v !== null && $v !== '') {
+                return (string)$v;
+            }
+        }
+
         $candidates = ['key', 'userId', 'id', 'email'];
         foreach ($candidates as $attr) {
             $v = $context->get($attr);
@@ -51,10 +109,8 @@ final class Evaluator
 
     private function computeBucket(string $flagName, string $key): int
     {
-        $hash = crc32($flagName . ':' . $key);
-        // Normalize to unsigned 32-bit to avoid negative values on some platforms
-        $unsigned = (int) sprintf('%u', $hash);
-        // Map to 0..99
-        return (int)($unsigned % 100);
+        $hash = hash('xxh3', $flagName . ':' . $key);
+
+        return (int)(hexdec(substr($hash, 0, 8)) % 100);
     }
 }
diff --git a/src/FeatureManager.php b/src/FeatureManager.php
index 0780b46..860df9f 100644
--- a/src/FeatureManager.php
+++ b/src/FeatureManager.php
@@ -5,13 +5,18 @@ declare(strict_types=1);
 namespace FlagPole;
 
 use FlagPole\Repository\FlagRepositoryInterface;
+use Psr\Log\LoggerInterface;
 
 final class FeatureManager
 {
+    private Evaluator $evaluator;
+
     public function __construct(
         private FlagRepositoryInterface $repository,
-        private Evaluator $evaluator = new Evaluator()
+        ?Evaluator $evaluator = null,
+        ?LoggerInterface $logger = null
     ) {
+        $this->evaluator = $evaluator ?? new Evaluator($logger);
     }
 
     public function isEnabled(string $flagName, ?Context $context = null, bool $default = false): bool
diff --git a/src/Flag.php b/src/Flag.php
index a983c76..f2605ff 100644
--- a/src/Flag.php
+++ b/src/Flag.php
@@ -15,6 +15,9 @@ final class Flag
         public readonly ?int $rolloutPercentage = null,
         /** @var list<string> */
         public readonly array $allowList = [],
+        /** @var list<Rule> */
+        public readonly array $rules = [],
+        public readonly ?string $targetingKey = null,
     ) {
         if ($this->rolloutPercentage !== null) {
             if ($this->rolloutPercentage < 0 || $this->rolloutPercentage > 100) {
diff --git a/src/FlagHydrator.php b/src/FlagHydrator.php
new file mode 100644
index 0000000..6a6fb26
--- /dev/null
+++ b/src/FlagHydrator.php
@@ -0,0 +1,51 @@
+<?php
+
+declare(strict_types=1);
+
+namespace FlagPole;
+
+/**
+ * Hydrates Flag objects from raw configuration arrays.
+ */
+final class FlagHydrator
+{
+    private const VALID_OPERATORS = [
+        'eq', 'neq', 'gt', 'gte', 'lt', 'lte', 'in', 'nin', 'contains'
+    ];
+
+    /**
+     * @param string $name
+     * @param array{enabled?:bool|null, rolloutPercentage?:int|null, allowList?:list<string>, rules?:list<array{attribute:string, operator:string, value:mixed}>, targetingKey?:string|null} $data
+     * @return Flag
+     */
+    public function hydrate(string $name, array $data): Flag
+    {
+        $rules = [];
+        if (isset($data['rules']) && is_array($data['rules'])) {
+            foreach ($data['rules'] as $ruleDef) {
+                if (!isset($ruleDef['attribute'], $ruleDef['operator'], $ruleDef['value'])) {
+                    throw new \InvalidArgumentException(sprintf('Invalid rule definition for flag "%s". Missing attribute, operator, or value.', $name));
+                }
+
+                if (!in_array($ruleDef['operator'], self::VALID_OPERATORS, true)) {
+                    throw new \InvalidArgumentException(sprintf('Invalid operator "%s" for flag "%s".', $ruleDef['operator'], $name));
+                }
+
+                $rules[] = new Rule(
+                    attribute: $ruleDef['attribute'],
+                    operator: $ruleDef['operator'],
+                    value: $ruleDef['value']
+                );
+            }
+        }
+
+        return new Flag(
+            name: $name,
+            enabled: $data['enabled'] ?? null,
+            rolloutPercentage: $data['rolloutPercentage'] ?? null,
+            allowList: $data['allowList'] ?? [],
+            rules: $rules,
+            targetingKey: $data['targetingKey'] ?? null
+        );
+    }
+}
diff --git a/src/Repository/InMemoryFlagRepository.php b/src/Repository/InMemoryFlagRepository.php
index 5714d1a..b02daa0 100644
--- a/src/Repository/InMemoryFlagRepository.php
+++ b/src/Repository/InMemoryFlagRepository.php
@@ -5,6 +5,8 @@ declare(strict_types=1);
 namespace FlagPole\Repository;
 
 use FlagPole\Flag;
+use FlagPole\FlagHydrator;
+use FlagPole\Rule;
 
 /**
  * Simple in-memory repository. Useful for bootstrapping or tests.
@@ -15,18 +17,14 @@ final class InMemoryFlagRepository implements FlagRepositoryInterface
     private array $flags = [];
 
     /**
-     * @param array<string, array{enabled?:bool|null, rolloutPercentage?:int|null, allowList?:list<string>}> $config
+     * @param array<string, array{enabled?:bool|null, rolloutPercentage?:int|null, allowList?:list<string>, rules?:list<array{attribute:string, operator:string, value:mixed}>, targetingKey?:string|null}> $config
      */
     public static function fromArray(array $config): self
     {
+        $hydrator = new FlagHydrator();
         $items = [];
         foreach ($config as $name => $def) {
-            $items[$name] = new Flag(
-                name: (string)$name,
-                enabled: $def['enabled'] ?? null,
-                rolloutPercentage: $def['rolloutPercentage'] ?? null,
-                allowList: $def['allowList'] ?? []
-            );
+            $items[$name] = $hydrator->hydrate((string)$name, $def);
         }
         return new self($items);
     }
diff --git a/src/Rule.php b/src/Rule.php
new file mode 100644
index 0000000..ca99e27
--- /dev/null
+++ b/src/Rule.php
@@ -0,0 +1,18 @@
+<?php
+
+declare(strict_types=1);
+
+namespace FlagPole;
+
+/**
+ * A rule defines a condition that must be met for a flag to be enabled.
+ */
+final class Rule
+{
+    public function __construct(
+        public readonly string $attribute,
+        public readonly string $operator,
+        public readonly mixed $value,
+    ) {
+    }
+}
diff --git a/tests/ComprehensiveTest.php b/tests/ComprehensiveTest.php
new file mode 100644
index 0000000..a64dae1
--- /dev/null
+++ b/tests/ComprehensiveTest.php
@@ -0,0 +1,107 @@
+<?php
+
+declare(strict_types=1);
+
+namespace FlagPole\Tests;
+
+use FlagPole\Context;
+use FlagPole\Evaluator;
+use FlagPole\Flag;
+use FlagPole\FlagHydrator;
+use FlagPole\Rule;
+use PHPUnit\Framework\TestCase;
+
+final class ComprehensiveTest extends TestCase
+{
+    public function testFlagValidation(): void
+    {
+        $this->expectException(\InvalidArgumentException::class);
+        $this->expectExceptionMessage('rolloutPercentage must be between 0 and 100');
+        new Flag('invalid', rolloutPercentage: 101);
+    }
+
+    public function testFlagValidationNegative(): void
+    {
+        $this->expectException(\InvalidArgumentException::class);
+        $this->expectExceptionMessage('rolloutPercentage must be between 0 and 100');
+        new Flag('invalid', rolloutPercentage: -1);
+    }
+
+    public function testHydratorMissingFields(): void
+    {
+        $hydrator = new FlagHydrator();
+        $this->expectException(\InvalidArgumentException::class);
+        $this->expectExceptionMessage('Invalid rule definition for flag "test". Missing attribute, operator, or value.');
+        $hydrator->hydrate('test', [
+            'rules' => [
+                ['attribute' => 'plan'] // missing operator and value
+            ]
+        ]);
+    }
+
+    public function testHydratorInvalidOperator(): void
+    {
+        $hydrator = new FlagHydrator();
+        $this->expectException(\InvalidArgumentException::class);
+        $this->expectExceptionMessage('Invalid operator "invalid_op" for flag "test".');
+        $hydrator->hydrate('test', [
+            'rules' => [
+                ['attribute' => 'plan', 'operator' => 'invalid_op', 'value' => 'pro']
+            ]
+        ]);
+    }
+
+    /**
+     * @dataProvider operatorProvider
+     */
+    public function testAllOperators(string $operator, mixed $ruleValue, mixed $contextValue, bool $expected): void
+    {
+        $evaluator = new Evaluator();
+        $flag = new Flag('test', rules: [
+            new Rule('attr', $operator, $ruleValue)
+        ]);
+        $context = Context::fromArray(['attr' => $contextValue]);
+
+        $this->assertSame($expected, $evaluator->evaluate($flag, $context));
+    }
+
+    public static function operatorProvider(): array
+    {
+        return [
+            'eq match' => ['eq', 'val', 'val', true],
+            'eq mismatch' => ['eq', 'val', 'other', false],
+            'neq match' => ['neq', 'val', 'other', true],
+            'neq mismatch' => ['neq', 'val', 'val', false],
+            'gt match' => ['gt', 10, 11, true],
+            'gt mismatch' => ['gt', 10, 10, false],
+            'gte match eq' => ['gte', 10, 10, true],
+            'gte match gt' => ['gte', 10, 11, true],
+            'gte mismatch' => ['gte', 10, 9, false],
+            'lt match' => ['lt', 10, 9, true],
+            'lt mismatch' => ['lt', 10, 10, false],
+            'lte match eq' => ['lte', 10, 10, true],
+            'lte match lt' => ['lte', 10, 9, true],
+            'lte mismatch' => ['lte', 10, 11, false],
+            'in match' => ['in', ['a', 'b'], 'a', true],
+            'in mismatch' => ['in', ['a', 'b'], 'c', false],
+            'nin match' => ['nin', ['a', 'b'], 'c', true],
+            'nin mismatch' => ['nin', ['a', 'b'], 'a', false],
+            'contains match' => ['contains', 'foo', 'foobar', true],
+            'contains mismatch' => ['contains', 'baz', 'foobar', false],
+        ];
+    }
+
+    public function testRuntimeUnsupportedOperator(): void
+    {
+        $evaluator = new Evaluator();
+        // We bypass the hydrator which has validation to test the evaluator safety
+        $flag = new Flag('test', rules: [
+            new Rule('attr', 'unsupported', 'val')
+        ]);
+        $context = Context::fromArray(['attr' => 'val']);
+
+        $this->expectException(\LogicException::class);
+        $this->expectExceptionMessage('Unsupported operator "unsupported" encountered during evaluation.');
+        $evaluator->evaluate($flag, $context);
+    }
+}
diff --git a/tests/FeatureManagerTest.php b/tests/FeatureManagerTest.php
index 9952898..b8f2a04 100644
--- a/tests/FeatureManagerTest.php
+++ b/tests/FeatureManagerTest.php
@@ -8,6 +8,7 @@ use FlagPole\Context;
 use FlagPole\FeatureManager;
 use FlagPole\Repository\InMemoryFlagRepository;
 use PHPUnit\Framework\TestCase;
+use Psr\Log\AbstractLogger;
 
 final class FeatureManagerTest extends TestCase
 {
@@ -23,6 +24,27 @@ final class FeatureManagerTest extends TestCase
         $this->assertFalse($fm->isEnabled('hard-off', null, true));
     }
 
+    public function testLogging(): void
+    {
+        $logger = new class extends AbstractLogger {
+            public array $logs = [];
+            public function log($level, string|\Stringable $message, array $context = []): void
+            {
+                $this->logs[] = (string)$message;
+            }
+        };
+
+        $repo = InMemoryFlagRepository::fromArray([
+            'test-flag' => ['enabled' => true],
+        ]);
+        $fm = new FeatureManager($repo, null, $logger);
+
+        $fm->isEnabled('test-flag');
+
+        $this->assertCount(1, $logger->logs);
+        $this->assertStringContainsString('Flag "test-flag" evaluated to TRUE via explicit "enabled" override', $logger->logs[0]);
+    }
+
     public function testAllowListWins(): void
     {
         $repo = InMemoryFlagRepository::fromArray([
@@ -116,4 +138,70 @@ final class FeatureManagerTest extends TestCase
         $this->assertFalse($fm->isEnabled('gradual', $emptyCtx, false));
         $this->assertTrue($fm->isEnabled('gradual', $emptyCtx, true));
     }
+
+    public function testRulesMatching(): void
+    {
+        $repo = InMemoryFlagRepository::fromArray([
+            'beta-users' => [
+                'rules' => [
+                    ['attribute' => 'group', 'operator' => 'eq', 'value' => 'beta'],
+                ],
+            ],
+            'version-check' => [
+                'rules' => [
+                    ['attribute' => 'version', 'operator' => 'gte', 'value' => '2.0'],
+                ],
+            ],
+            'multi-rules' => [
+                'rules' => [
+                    ['attribute' => 'plan', 'operator' => 'in', 'value' => ['pro', 'enterprise']],
+                    ['attribute' => 'region', 'operator' => 'eq', 'value' => 'us-east'],
+                ],
+            ],
+        ]);
+        $fm = new FeatureManager($repo);
+
+        // Single rule 'eq'
+        $this->assertTrue($fm->isEnabled('beta-users', Context::fromArray(['group' => 'beta'])));
+        $this->assertFalse($fm->isEnabled('beta-users', Context::fromArray(['group' => 'standard'])));
+
+        // Single rule 'gte'
+        $this->assertTrue($fm->isEnabled('version-check', Context::fromArray(['version' => '2.0'])));
+        $this->assertTrue($fm->isEnabled('version-check', Context::fromArray(['version' => '2.1'])));
+        $this->assertFalse($fm->isEnabled('version-check', Context::fromArray(['version' => '1.9'])));
+
+        // Multi rules (OR behavior because it matches ANY rule in the list as implemented currently)
+        // Wait, the plan said: "Precedence: allowList > enabled > rules > rolloutPercentage"
+        // And the implementation I did:
+        /*
+        if (!empty($flag->rules)) {
+            foreach ($flag->rules as $rule) {
+                if ($this->matchRule($rule, $context)) {
+                    return true;
+                }
+            }
+        }
+        */
+        // This is indeed OR behavior. If ANY rule matches, it returns true.
+        $this->assertTrue($fm->isEnabled('multi-rules', Context::fromArray(['plan' => 'pro'])));
+        $this->assertTrue($fm->isEnabled('multi-rules', Context::fromArray(['region' => 'us-east'])));
+        $this->assertFalse($fm->isEnabled('multi-rules', Context::fromArray(['plan' => 'free', 'region' => 'eu-west'])));
+    }
+
+    public function testExplicitTargetingKey(): void
+    {
+        $repo = InMemoryFlagRepository::fromArray([
+            'custom-key' => [
+                'targetingKey' => 'orgId',
+                'allowList' => ['org_123'],
+            ],
+        ]);
+        $fm = new FeatureManager($repo);
+
+        $ctxMatched = Context::fromArray(['orgId' => 'org_123']);
+        $ctxUnmatched = Context::fromArray(['orgId' => 'org_456', 'userId' => 'org_123']); // userId matches but orgId doesn't
+
+        $this->assertTrue($fm->isEnabled('custom-key', $ctxMatched));
+        $this->assertFalse($fm->isEnabled('custom-key', $ctxUnmatched));
+    }
 }