diff --git a/src/Mod/Hub/Controllers/TeapotController.php b/src/Mod/Hub/Controllers/TeapotController.php
index d50113b..053e1af 100644
--- a/src/Mod/Hub/Controllers/TeapotController.php
+++ b/src/Mod/Hub/Controllers/TeapotController.php
@@ -75,7 +75,7 @@ class TeapotController
     }
 
     /**
-     * Remove sensitive headers before storing.
+     * Remove sensitive headers and enforce size limits before storing.
      */
     protected function sanitizeHeaders(array $headers): array
     {
@@ -85,6 +85,11 @@ class TeapotController
             unset($headers[$key]);
         }
 
+        // Enforce header count limit before passing to the model
+        if (count($headers) > HoneypotHit::HEADERS_MAX_COUNT) {
+            $headers = array_slice($headers, 0, HoneypotHit::HEADERS_MAX_COUNT, true);
+        }
+
         return $headers;
     }
 
diff --git a/src/Mod/Hub/Models/HoneypotHit.php b/src/Mod/Hub/Models/HoneypotHit.php
index 5373e89..0a5ed8b 100644
--- a/src/Mod/Hub/Models/HoneypotHit.php
+++ b/src/Mod/Hub/Models/HoneypotHit.php
@@ -27,6 +27,61 @@ class HoneypotHit extends Model
         'is_bot' => 'boolean',
     ];
 
+    /**
+     * Maximum number of headers to store per hit.
+     */
+    public const HEADERS_MAX_COUNT = 50;
+
+    /**
+     * Maximum size in bytes for the serialised headers JSON (16 KB).
+     */
+    public const HEADERS_MAX_SIZE = 16_384;
+
+    /**
+     * Validate and set the headers attribute, enforcing count and size limits.
+     */
+    public function setHeadersAttribute(mixed $value): void
+    {
+        if (is_null($value)) {
+            $this->attributes['headers'] = null;
+
+            return;
+        }
+
+        if (is_string($value)) {
+            $decoded = json_decode($value, true);
+            if (json_last_error() !== JSON_ERROR_NONE) {
+                $this->attributes['headers'] = null;
+
+                return;
+            }
+            $value = $decoded;
+        }
+
+        if (! is_array($value)) {
+            $this->attributes['headers'] = null;
+
+            return;
+        }
+
+        // Limit header count
+        if (count($value) > self::HEADERS_MAX_COUNT) {
+            $value = array_slice($value, 0, self::HEADERS_MAX_COUNT, true);
+        }
+
+        // Check total size and truncate further if needed
+        $json = json_encode($value);
+        if (strlen($json) > self::HEADERS_MAX_SIZE) {
+            // Progressively reduce until under limit
+            while (strlen($json) > self::HEADERS_MAX_SIZE && count($value) > 0) {
+                array_pop($value);
+                $json = json_encode($value);
+            }
+        }
+
+        $this->attributes['headers'] = $json;
+    }
+
     /**
      * Severity levels for honeypot hits.
      *
diff --git a/src/Mod/Hub/Models/Service.php b/src/Mod/Hub/Models/Service.php
index edf4884..6e23a83 100644
--- a/src/Mod/Hub/Models/Service.php
+++ b/src/Mod/Hub/Models/Service.php
@@ -6,6 +6,7 @@ namespace Core\Mod\Hub\Models;
 
 use Illuminate\Database\Eloquent\Builder;
 use Illuminate\Database\Eloquent\Model;
+use InvalidArgumentException;
 
 class Service extends Model
 {
@@ -121,6 +122,55 @@ class Service extends Model
         return null;
     }
 
+    /**
+     * Maximum size in bytes for the serialised metadata JSON (64 KB).
+     */
+    public const METADATA_MAX_SIZE = 65_535;
+
+    /**
+     * Maximum number of top-level keys allowed in metadata.
+     */
+    public const METADATA_MAX_KEYS = 100;
+
+    /**
+     * Validate and set the metadata attribute.
+     */
+    public function setMetadataAttribute(mixed $value): void
+    {
+        if (is_null($value)) {
+            $this->attributes['metadata'] = null;
+
+            return;
+        }
+
+        if (is_string($value)) {
+            $decoded = json_decode($value, true);
+            if (json_last_error() !== JSON_ERROR_NONE) {
+                throw new InvalidArgumentException('Metadata must be valid JSON');
+            }
+            $value = $decoded;
+        }
+
+        if (! is_array($value)) {
+            throw new InvalidArgumentException('Metadata must be an array or null');
+        }
+
+        if (count($value) > self::METADATA_MAX_KEYS) {
+            throw new InvalidArgumentException(
+                'Metadata exceeds maximum of ' . self::METADATA_MAX_KEYS . ' keys'
+            );
+        }
+
+        $json = json_encode($value);
+        if (strlen($json) > self::METADATA_MAX_SIZE) {
+            throw new InvalidArgumentException(
+                'Metadata exceeds maximum size of ' . self::METADATA_MAX_SIZE . ' bytes'
+            );
+        }
+
+        $this->attributes['metadata'] = $json;
+    }
+
     /**
      * Check if a specific metadata key exists.
      */
@@ -139,9 +189,17 @@ class Service extends Model
 
     /**
      * Set a metadata value.
+     *
+     * Keys must be non-empty and contain only alphanumeric characters, underscores, and hyphens.
      */
     public function setMeta(string $key, mixed $value): void
     {
+        if (empty($key) || ! preg_match('/^[a-zA-Z0-9_-]+$/', $key)) {
+            throw new InvalidArgumentException(
+                'Metadata key must be non-empty and contain only alphanumeric characters, underscores, and hyphens'
+            );
+        }
+
         $metadata = $this->metadata ?? [];
         $metadata[$key] = $value;
         $this->metadata = $metadata;
diff --git a/tests/Feature/Models/MetadataValidationTest.php b/tests/Feature/Models/MetadataValidationTest.php
new file mode 100644
index 0000000..7939efa
--- /dev/null
+++ b/tests/Feature/Models/MetadataValidationTest.php
@@ -0,0 +1,299 @@
+<?php
+
+/*
+ * Core PHP Framework
+ *
+ * Licensed under the European Union Public Licence (EUPL) v1.2.
+ * See LICENSE file for details.
+ */
+
+declare(strict_types=1);
+
+use Core\Mod\Hub\Models\HoneypotHit;
+use Core\Mod\Hub\Models\Service;
+
+/**
+ * Tests for JSON metadata field validation on Service and HoneypotHit models.
+ *
+ * Ensures size limits, key count limits, and key format validation
+ * are enforced to prevent mass assignment of arbitrary data.
+ */
+
+beforeEach(function () {
+    if (! \Illuminate\Support\Facades\Schema::hasTable('platform_services')) {
+        \Illuminate\Support\Facades\Schema::create('platform_services', function ($table) {
+            $table->id();
+            $table->string('code')->unique();
+            $table->string('module')->nullable();
+            $table->string('name');
+            $table->string('tagline')->nullable();
+            $table->text('description')->nullable();
+            $table->string('icon')->nullable();
+            $table->string('color')->nullable();
+            $table->string('marketing_domain')->nullable();
+            $table->string('website_class')->nullable();
+            $table->string('marketing_url')->nullable();
+            $table->string('docs_url')->nullable();
+            $table->boolean('is_enabled')->default(true);
+            $table->boolean('is_public')->default(true);
+            $table->boolean('is_featured')->default(false);
+            $table->string('entitlement_code')->nullable();
+            $table->integer('sort_order')->default(50);
+            $table->json('metadata')->nullable();
+            $table->timestamps();
+        });
+    }
+
+    if (! \Illuminate\Support\Facades\Schema::hasTable('honeypot_hits')) {
+        \Illuminate\Support\Facades\Schema::create('honeypot_hits', function ($table) {
+            $table->id();
+            $table->string('ip_address', 45);
+            $table->string('user_agent', 1000)->nullable();
+            $table->string('referer', 2000)->nullable();
+            $table->string('path', 255);
+            $table->string('method', 10);
+            $table->json('headers')->nullable();
+            $table->string('country', 2)->nullable();
+            $table->string('city', 100)->nullable();
+            $table->boolean('is_bot')->default(false);
+            $table->string('bot_name', 100)->nullable();
+            $table->string('severity', 20)->default('warning');
+            $table->timestamps();
+
+            $table->index('ip_address');
+            $table->index('created_at');
+            $table->index('is_bot');
+        });
+    }
+});
+
+afterEach(function () {
+    Service::query()->delete();
+    HoneypotHit::query()->delete();
+});
+
+// =============================================================================
+// Service Metadata Validation
+// =============================================================================
+
+describe('Service metadata validation', function () {
+    describe('setMetadataAttribute mutator', function () {
+        it('accepts valid metadata arrays', function () {
+            $service = new Service();
+            $service->metadata = ['key' => 'value', 'count' => 42];
+
+            expect($service->getAttributes()['metadata'])->toBe('{"key":"value","count":42}');
+        });
+
+        it('accepts null metadata', function () {
+            $service = new Service();
+            $service->metadata = null;
+
+            expect($service->getAttributes()['metadata'])->toBeNull();
+        });
+
+        it('accepts valid JSON strings', function () {
+            $service = new Service();
+            $service->metadata = '{"key":"value"}';
+
+            expect($service->getAttributes()['metadata'])->toBe('{"key":"value"}');
+        });
+
+        it('rejects invalid JSON strings', function () {
+            $service = new Service();
+
+            expect(fn () => $service->metadata = '{invalid json}')
+                ->toThrow(InvalidArgumentException::class, 'Metadata must be valid JSON');
+        });
+
+        it('rejects non-array non-string values', function () {
+            $service = new Service();
+
+            expect(fn () => $service->metadata = 12345)
+                ->toThrow(InvalidArgumentException::class, 'Metadata must be an array or null');
+        });
+
+        it('rejects metadata exceeding maximum key count', function () {
+            $service = new Service();
+            $data = [];
+            for ($i = 0; $i <= Service::METADATA_MAX_KEYS; $i++) {
+                $data["key_{$i}"] = 'value';
+            }
+
+            expect(fn () => $service->metadata = $data)
+                ->toThrow(InvalidArgumentException::class, 'Metadata exceeds maximum of');
+        });
+
+        it('accepts metadata at the maximum key count', function () {
+            $service = new Service();
+            $data = [];
+            for ($i = 0; $i < Service::METADATA_MAX_KEYS; $i++) {
+                $data["key_{$i}"] = 'v';
+            }
+
+            $service->metadata = $data;
+
+            expect(json_decode($service->getAttributes()['metadata'], true))
+                ->toHaveCount(Service::METADATA_MAX_KEYS);
+        });
+
+        it('rejects metadata exceeding maximum size', function () {
+            $service = new Service();
+            // Create a payload that exceeds 64KB
+            $data = ['large' => str_repeat('x', Service::METADATA_MAX_SIZE)];
+
+            expect(fn () => $service->metadata = $data)
+                ->toThrow(InvalidArgumentException::class, 'Metadata exceeds maximum size');
+        });
+
+        it('persists valid metadata to database', function () {
+            $service = Service::create([
+                'code' => 'test-service',
+                'name' => 'Test Service',
+                'metadata' => ['version' => '1.0', 'features' => ['a', 'b']],
+            ]);
+
+            $fresh = Service::find($service->id);
+            expect($fresh->metadata)->toBe(['version' => '1.0', 'features' => ['a', 'b']]);
+        });
+    });
+
+    describe('setMeta key validation', function () {
+        it('accepts valid alphanumeric keys', function () {
+            $service = new Service();
+            $service->metadata = [];
+
+            $service->setMeta('valid_key', 'value');
+            expect($service->metadata['valid_key'])->toBe('value');
+        });
+
+        it('accepts keys with hyphens', function () {
+            $service = new Service();
+            $service->metadata = [];
+
+            $service->setMeta('my-key', 'value');
+            expect($service->metadata['my-key'])->toBe('value');
+        });
+
+        it('rejects empty keys', function () {
+            $service = new Service();
+            $service->metadata = [];
+
+            expect(fn () => $service->setMeta('', 'value'))
+                ->toThrow(InvalidArgumentException::class);
+        });
+
+        it('rejects keys with special characters', function () {
+            $service = new Service();
+            $service->metadata = [];
+
+            expect(fn () => $service->setMeta('key.with.dots', 'value'))
+                ->toThrow(InvalidArgumentException::class);
+
+            expect(fn () => $service->setMeta('key with spaces', 'value'))
+                ->toThrow(InvalidArgumentException::class);
+
+            expect(fn () => $service->setMeta('key/path', 'value'))
+                ->toThrow(InvalidArgumentException::class);
+        });
+    });
+});
+
+// =============================================================================
+// HoneypotHit Headers Validation
+// =============================================================================
+
+describe('HoneypotHit headers validation', function () {
+    describe('setHeadersAttribute mutator', function () {
+        it('accepts valid header arrays', function () {
+            $hit = new HoneypotHit();
+            $hit->headers = ['host' => ['example.com'], 'accept' => ['text/html']];
+
+            $decoded = json_decode($hit->getAttributes()['headers'], true);
+            expect($decoded)->toHaveKey('host');
+            expect($decoded)->toHaveKey('accept');
+        });
+
+        it('accepts null headers', function () {
+            $hit = new HoneypotHit();
+            $hit->headers = null;
+
+            expect($hit->getAttributes()['headers'])->toBeNull();
+        });
+
+        it('truncates headers exceeding count limit', function () {
+            $hit = new HoneypotHit();
+            $headers = [];
+            for ($i = 0; $i < HoneypotHit::HEADERS_MAX_COUNT + 20; $i++) {
+                $headers["x-header-{$i}"] = ["value-{$i}"];
+            }
+
+            $hit->headers = $headers;
+
+            $decoded = json_decode($hit->getAttributes()['headers'], true);
+            expect(count($decoded))->toBeLessThanOrEqual(HoneypotHit::HEADERS_MAX_COUNT);
+        });
+
+        it('keeps headers at the exact limit', function () {
+            $hit = new HoneypotHit();
+            $headers = [];
+            for ($i = 0; $i < HoneypotHit::HEADERS_MAX_COUNT; $i++) {
+                $headers["h{$i}"] = ['v'];
+            }
+
+            $hit->headers = $headers;
+
+            $decoded = json_decode($hit->getAttributes()['headers'], true);
+            expect(count($decoded))->toBe(HoneypotHit::HEADERS_MAX_COUNT);
+        });
+
+        it('truncates headers exceeding size limit', function () {
+            $hit = new HoneypotHit();
+            // Create headers with large values that exceed 16KB
+            $headers = [];
+            for ($i = 0; $i < 10; $i++) {
+                $headers["x-large-{$i}"] = [str_repeat('x', 2000)];
+            }
+
+            $hit->headers = $headers;
+
+            $json = $hit->getAttributes()['headers'];
+            expect(strlen($json))->toBeLessThanOrEqual(HoneypotHit::HEADERS_MAX_SIZE);
+        });
+
+        it('handles invalid JSON string gracefully', function () {
+            $hit = new HoneypotHit();
+            $hit->headers = '{not valid json}';
+
+            expect($hit->getAttributes()['headers'])->toBeNull();
+        });
+
+        it('handles non-array non-string values gracefully', function () {
+            $hit = new HoneypotHit();
+            $hit->headers = 12345;
+
+            expect($hit->getAttributes()['headers'])->toBeNull();
+        });
+
+        it('accepts valid JSON strings', function () {
+            $hit = new HoneypotHit();
+            $hit->headers = '{"host":["example.com"]}';
+
+            $decoded = json_decode($hit->getAttributes()['headers'], true);
+            expect($decoded)->toHaveKey('host');
+        });
+
+        it('persists valid headers to database', function () {
+            $hit = HoneypotHit::create([
+                'ip_address' => '192.168.1.1',
+                'path' => '/teapot',
+                'method' => 'GET',
+                'headers' => ['host' => ['example.com'], 'accept' => ['*/*']],
+                'severity' => 'warning',
+            ]);
+
+            $fresh = HoneypotHit::find($hit->id);
+            expect($fresh->headers)->toBe(['host' => ['example.com'], 'accept' => ['*/*']]);
+        });
+    });
+});