diff --git a/src/Bundle/ChillPersonBundle/PersonIdentifier/Identifier/StringIdentifier.php b/src/Bundle/ChillPersonBundle/PersonIdentifier/Identifier/StringIdentifier.php
index 4bc02c117..c570cd79b 100644
--- a/src/Bundle/ChillPersonBundle/PersonIdentifier/Identifier/StringIdentifier.php
+++ b/src/Bundle/ChillPersonBundle/PersonIdentifier/Identifier/StringIdentifier.php
@@ -16,11 +16,15 @@ use Chill\PersonBundle\Entity\Identifier\PersonIdentifierDefinition;
 use Chill\PersonBundle\PersonIdentifier\PersonIdentifierEngineInterface;
 use Symfony\Component\Form\Extension\Core\Type\TextType;
 use Symfony\Component\Form\FormBuilderInterface;
+use Symfony\Component\Validator\Context\ExecutionContextInterface;
 
 final readonly class StringIdentifier implements PersonIdentifierEngineInterface
 {
     public const NAME = 'chill-person-bundle.string-identifier';
 
+    private const ONLY_NUMBERS = 'only_numbers';
+    private const FIXED_LENGTH = 'fixed_length';
+
     public static function getName(): string
     {
         return self::NAME;
@@ -45,4 +49,21 @@ final readonly class StringIdentifier implements PersonIdentifierEngineInterface
     {
         return '' === trim($identifier->getValue()['content'] ?? '');
     }
+
+    public function validate(ExecutionContextInterface $context, PersonIdentifier $identifier, PersonIdentifierDefinition $definition): void
+    {
+        $config = $definition->getData();
+        $content = (string) ($identifier->getValue()['content'] ?? '');
+
+        if (($config[self::ONLY_NUMBERS] ?? false) && !preg_match('/^[0-9]+$/', $content)) {
+            $context->buildViolation('person_identifier.only_number')
+                ->addViolation();
+        }
+
+        if (null !== ($config[self::FIXED_LENGTH] ?? null) && strlen($content) !== $config[self::FIXED_LENGTH]) {
+            $context->buildViolation('person_identifier.fixed_length')
+                ->setParameter('limit', (string) $config[self::FIXED_LENGTH])
+                ->addViolation();
+        }
+    }
 }
diff --git a/src/Bundle/ChillPersonBundle/Tests/PersonIdentifier/Identifier/StringIdentifierValidationTest.php b/src/Bundle/ChillPersonBundle/Tests/PersonIdentifier/Identifier/StringIdentifierValidationTest.php
new file mode 100644
index 000000000..3b8190896
--- /dev/null
+++ b/src/Bundle/ChillPersonBundle/Tests/PersonIdentifier/Identifier/StringIdentifierValidationTest.php
@@ -0,0 +1,128 @@
+<?php
+
+declare(strict_types=1);
+
+/*
+ * Chill is a software for social workers
+ *
+ * For the full copyright and license information, please view
+ * the LICENSE file that was distributed with this source code.
+ */
+
+namespace Chill\PersonBundle\Tests\PersonIdentifier\Identifier;
+
+use Chill\PersonBundle\Entity\Identifier\PersonIdentifier;
+use Chill\PersonBundle\Entity\Identifier\PersonIdentifierDefinition;
+use Chill\PersonBundle\PersonIdentifier\Identifier\StringIdentifier;
+use PHPUnit\Framework\MockObject\MockObject;
+use PHPUnit\Framework\TestCase;
+use Symfony\Component\Validator\Context\ExecutionContextInterface;
+use Symfony\Component\Validator\Violation\ConstraintViolationBuilderInterface;
+
+/**
+ * @internal
+ *
+ * @coversNothing
+ */
+class StringIdentifierValidationTest extends TestCase
+{
+    private function makeDefinition(array $data = []): PersonIdentifierDefinition
+    {
+        return new PersonIdentifierDefinition(label: ['en' => 'String'], engine: StringIdentifier::getName(), data: $data);
+    }
+
+    private function makeIdentifier(PersonIdentifierDefinition $definition, string $content): PersonIdentifier
+    {
+        $identifier = new PersonIdentifier($definition);
+        $identifier->setValue(['content' => $content]);
+
+        return $identifier;
+    }
+
+    /**
+     * Helper creating a context mock expecting zero violations.
+     */
+    private function expectNoViolation(): ExecutionContextInterface
+    {
+        $context = $this->createMock(ExecutionContextInterface::class);
+        $context->expects(self::never())->method('buildViolation');
+
+        return $context;
+    }
+
+    /**
+     * Helper creating a context mock expecting a single violation with a given message and optional parameters chain.
+     */
+    private function expectSingleViolation(string $message, array $parameters = []): ExecutionContextInterface
+    {
+        /** @var ConstraintViolationBuilderInterface&MockObject $builder */
+        $builder = $this->createMock(ConstraintViolationBuilderInterface::class);
+
+        // If parameters are provided, ensure setParameter is called with each, in any order, and returns builder for chaining
+        if ($parameters) {
+            foreach ($parameters as $name => $value) {
+                $builder->expects(self::atLeastOnce())
+                    ->method('setParameter')
+                    ->with($name, $value)
+                    ->willReturn($builder);
+            }
+        } else {
+            $builder->expects(self::any())->method('setParameter')->willReturn($builder);
+        }
+
+        $builder->expects(self::once())->method('addViolation');
+
+        $context = $this->createMock(ExecutionContextInterface::class);
+        $context->expects(self::once())
+            ->method('buildViolation')
+            ->with($message)
+            ->willReturn($builder);
+
+        return $context;
+    }
+
+    public function testNoOptionsAcceptsAnyString(): void
+    {
+        $engine = new StringIdentifier();
+        $definition = $this->makeDefinition([]);
+        $identifier = $this->makeIdentifier($definition, 'abc123');
+
+        $engine->validate($this->expectNoViolation(), $identifier, $definition);
+    }
+
+    public function testOnlyNumbersValid(): void
+    {
+        $engine = new StringIdentifier();
+        $definition = $this->makeDefinition(['only_numbers' => true]);
+        $identifier = $this->makeIdentifier($definition, '123456');
+
+        $engine->validate($this->expectNoViolation(), $identifier, $definition);
+    }
+
+    public function testOnlyNumbersInvalid(): void
+    {
+        $engine = new StringIdentifier();
+        $definition = $this->makeDefinition(['only_numbers' => true]);
+        $identifier = $this->makeIdentifier($definition, '12AB');
+
+        $engine->validate($this->expectSingleViolation('person_identifier.only_number'), $identifier, $definition);
+    }
+
+    public function testFixedLengthValid(): void
+    {
+        $engine = new StringIdentifier();
+        $definition = $this->makeDefinition(['fixed_length' => 5]);
+        $identifier = $this->makeIdentifier($definition, '12345');
+
+        $engine->validate($this->expectNoViolation(), $identifier, $definition);
+    }
+
+    public function testFixedLengthInvalid(): void
+    {
+        $engine = new StringIdentifier();
+        $definition = $this->makeDefinition(['fixed_length' => 5]);
+        $identifier = $this->makeIdentifier($definition, '1234');
+
+        $engine->validate($this->expectSingleViolation('person_identifier.fixed_length', ['limit' => 5]), $identifier, $definition);
+    }
+}