diff --git a/docs/examples/05-schema-validation-of-paramters.md b/docs/examples/05-schema-validation-of-paramters.md
new file mode 100644
index 0000000..f117fab
--- /dev/null
+++ b/docs/examples/05-schema-validation-of-paramters.md
@@ -0,0 +1,24 @@
+# Validating parameters with JSON schema
+
+As templates become more and more complex, the required parameters needed to render an email can become large and complex too.
+It's easy to omit a parameter, or forget what parameters are needed to be submitted for any given template. A mistake here, can result in
+your template language throwing an error, and a 500 response.
+
+In order to minimise this, you can optionally define a JSON schema which runtime parameters will be validated against.
+
+So you've got the hello world working, and you want to try a real template.
+
+Simply define your JSON schema next to your template's meta file, e.g. `hello-world/hello-world.schema.json`:
+
+```json
+{
+  "$schema": "http://json-schema.org/draft-06/schema#",
+  "properties": {
+    "email": {
+      "type": "string",
+      "format": "email"
+    },
+    "required": ["email"]
+  }
+}
+```
diff --git a/docs/examples/hello-world/hello-world.schema.json b/docs/examples/hello-world/hello-world.schema.json
new file mode 100644
index 0000000..ebc7719
--- /dev/null
+++ b/docs/examples/hello-world/hello-world.schema.json
@@ -0,0 +1,10 @@
+{
+  "$schema": "http://json-schema.org/draft-06/schema#",
+  "properties": {
+    "email": {
+      "type": "string",
+      "format": "email"
+    },
+    "required": ["email"]
+  }
+}
diff --git a/src/AppBundle/Controller/OutboxController.php b/src/AppBundle/Controller/OutboxController.php
index 09c1e90..8de9348 100644
--- a/src/AppBundle/Controller/OutboxController.php
+++ b/src/AppBundle/Controller/OutboxController.php
@@ -8,6 +8,7 @@
 use Outstack\Enveloper\Mail\Participants\Participant;
 use Outstack\Enveloper\Outbox;
 use Outstack\Enveloper\PipeprintBridge\Exceptions\PipelineFailed;
+use Outstack\Enveloper\Resolution\ParametersFailedSchemaValidation;
 use Symfony\Bundle\FrameworkBundle\Controller\Controller;
 use Symfony\Component\HttpFoundation\Request;
 use Symfony\Component\HttpFoundation\Response;
@@ -45,7 +46,7 @@ public function postAction(Request $request)
         $outbox = $this->outbox;
         $payload = json_decode($request->getContent());
 
-        $dereferencer  = \League\JsonReference\Dereferencer::draft4();
+        $dereferencer  = \League\JsonReference\Dereferencer::draft6();
         $schema        = $dereferencer->dereference('file://' . $this->container->getParameter('kernel.root_dir'). '/../schemata/outbox_post.json');
 
         $validator     = new \League\JsonGuard\Validator($payload, $schema);
@@ -74,6 +75,20 @@ function(ValidationError $e) {
                 ->setDetail($e->getMessage())
                 ->addField('pipeprintError', $e->getErrorData())
                 ->buildJsonResponse();
+        } catch (ParametersFailedSchemaValidation $e) {
+            return $this->problemFactory
+                ->createProblem(400, 'Parameters failed JSON schema validation')
+                ->setDetail('A template was found but the parameters submitted to it do not validate against the configured JSON schema')
+                ->addField('errors', array_map(
+                        function(ValidationError $e) {
+                            return [
+                                'error' => $e->getMessage(),
+                                'path' => $e->getSchemaPath()
+                            ];
+                        }, $e->getErrors())
+                )
+                ->buildJsonResponse();
+
         }
     }
 
diff --git a/src/Outstack/Enveloper/Resolution/MessageResolver.php b/src/Outstack/Enveloper/Resolution/MessageResolver.php
index dd16cbb..1bf0e21 100644
--- a/src/Outstack/Enveloper/Resolution/MessageResolver.php
+++ b/src/Outstack/Enveloper/Resolution/MessageResolver.php
@@ -60,6 +60,17 @@ public function __construct(
 
     public function resolve(Template $template, object $parameters): Message
     {
+        if (!is_null($template->getSchema())) {
+            $dereferencer  = \League\JsonReference\Dereferencer::draft6();
+            $schema        = $dereferencer->dereference($template->getSchema());
+
+            $validator     = new \League\JsonGuard\Validator($parameters, $schema);
+            if ($validator->fails()) {
+                throw new ParametersFailedSchemaValidation($validator->errors());
+            }
+
+        }
+
         if (is_null($template->getSender())) {
             $from = new Participant($this->defaultSenderName, new EmailAddress($this->defaultSenderEmail));
         } else {
diff --git a/src/Outstack/Enveloper/Resolution/ParametersFailedSchemaValidation.php b/src/Outstack/Enveloper/Resolution/ParametersFailedSchemaValidation.php
new file mode 100644
index 0000000..5f24e04
--- /dev/null
+++ b/src/Outstack/Enveloper/Resolution/ParametersFailedSchemaValidation.php
@@ -0,0 +1,19 @@
+<?php
+
+namespace Outstack\Enveloper\Resolution;
+
+class ParametersFailedSchemaValidation extends \RuntimeException
+{
+    private $errors;
+
+    public function __construct(array $validationErrors)
+    {
+        parent::__construct("Parameters failed schema validation");
+        $this->errors = $validationErrors;
+    }
+
+    public function getErrors(): array
+    {
+        return $this->errors;
+    }
+}
\ No newline at end of file
diff --git a/src/Outstack/Enveloper/Templates/Loader/FilesystemLoader.php b/src/Outstack/Enveloper/Templates/Loader/FilesystemLoader.php
index c4a1f39..da285b6 100644
--- a/src/Outstack/Enveloper/Templates/Loader/FilesystemLoader.php
+++ b/src/Outstack/Enveloper/Templates/Loader/FilesystemLoader.php
@@ -32,6 +32,7 @@ public function __construct(Filesystem $filesystem)
     public function find(string $name): Template
     {
         $configPath = "$name/$name.meta.yml";
+        $schemaPath = "$name/$name.schema.json";
 
         try {
             $config = Yaml::parse(
@@ -45,6 +46,11 @@ public function find(string $name): Template
 
         $config = $this->normaliseConfig($config);
 
+        $schema = null;
+        if ($this->filesystem->has($schemaPath)) {
+            $schema = json_decode($this->filesystem->read($schemaPath));
+        }
+
         $textTemplate = null;
         if (!is_null($config['content']['text'])) {
             $textTemplate = $this->filesystem->read("$name/{$config['content']['text']}");
@@ -52,6 +58,7 @@ public function find(string $name): Template
 
         $htmlTemplate = $this->filesystem->read("$name/{$config['content']['html']}");
         return new Template(
+            $schema,
             $config['subject'],
             array_key_exists('from', $config) ? $this->parseRecipientTemplate($config['from']) : null,
             $this->parseRecipientListTemplate($config['recipients']['to']),
diff --git a/src/Outstack/Enveloper/Templates/Template.php b/src/Outstack/Enveloper/Templates/Template.php
index 449e3f9..6bc7135 100644
--- a/src/Outstack/Enveloper/Templates/Template.php
+++ b/src/Outstack/Enveloper/Templates/Template.php
@@ -45,8 +45,13 @@ class Template
      * @var string
      */
     private $htmlTemplateName;
+    /**
+     * @var object
+     */
+    private $schema;
 
     public function __construct(
+        ?object $schema,
         string $subject,
         ?ParticipantTemplate $sender,
         ParticipantListTemplate $recipientsTo,
@@ -68,6 +73,12 @@ public function __construct(
         $this->htmlTemplateName = $htmlTemplateName;
         $this->sender = $sender;
         $this->attachments = $attachments;
+        $this->schema = $schema;
+    }
+
+    public function getSchema(): ?object
+    {
+        return $this->schema;
     }
 
     /**
diff --git a/tests/Functional/ErrorHandlingFunctionalTest.php b/tests/Functional/ErrorHandlingFunctionalTest.php
index eff2185..39af7e9 100644
--- a/tests/Functional/ErrorHandlingFunctionalTest.php
+++ b/tests/Functional/ErrorHandlingFunctionalTest.php
@@ -120,4 +120,56 @@ public function test_syntax_error_is_nicely_formatted()
         throw new \LogicException("Expected HttpException, none caught");
 
     }
+
+    public function test_parameters_sent_to_template_are_validated_by_schema()
+    {
+        $convertToStream = function($str) {
+            $stream = fopen("php://temp", 'r+');
+            fputs($stream, $str);
+            rewind($stream);
+            return $stream;
+        };
+
+        $request = new Request(
+            '/outbox',
+            'POST',
+            $convertToStream(json_encode([
+                'template' => 'message-with-attachments',
+                'parameters' => [
+                    'email' => 'bob@example.com',
+                    'attachments' => [
+                        ['contents' => 'This is a note', 'filename' => '']
+                    ]
+                ]
+            ]))
+        );
+
+        try {
+            $this->client->sendRequest($request);
+        } catch (HttpException $e) {
+
+            $response   = $e->getResponse();
+            $body       = (string) $response->getBody();
+
+            $this->assertEquals(400, $response->getStatusCode());
+            $this->assertJson($body);
+            $this->assertEquals([
+                'title' => 'Parameters failed JSON schema validation',
+                'detail' => 'A template was found but the parameters submitted to it do not validate against the configured JSON schema',
+                'status' => 400,
+                'errors' => [
+                    [
+                        'error' => 'The string must be at least 1 characters long.',
+                        'path' => '/properties/attachments/items/0/properties/filename/minLength'
+                    ]
+                ]
+            ], json_decode($body, true));
+            $this->assertEquals('application/problem+json', $response->getHeaderLine('Content-type'));
+
+            return;
+        }
+
+        throw new \LogicException("Expected HttpException, none caught");
+
+    }
 }
\ No newline at end of file
diff --git a/tests/Unit/Outstack/Enveloper/Resolution/MessageResolverTest.php b/tests/Unit/Outstack/Enveloper/Resolution/MessageResolverTest.php
index f7c6925..427cccb 100644
--- a/tests/Unit/Outstack/Enveloper/Resolution/MessageResolverTest.php
+++ b/tests/Unit/Outstack/Enveloper/Resolution/MessageResolverTest.php
@@ -49,6 +49,7 @@ public function test_it_resolves_simplest_message()
 
         $message = $this->sut->resolve(
             new Template(
+                null,
                 'Welcome, {{ user.name }}',
                 new ParticipantTemplate(null, 'noreply@example.com'),
                 new ParticipantListTemplate([new ParticipantTemplate(null, '{{ user.email }}')]),
@@ -85,6 +86,7 @@ public function test_it_resolves_message_with_attachments()
 
         $message = $this->sut->resolve(
             new Template(
+                null,
                 'Welcome, {{ user.name }}',
                 new ParticipantTemplate(null, 'noreply@example.com'),
                 new ParticipantListTemplate([new ParticipantTemplate(null, '{{ user.email }}')]),
@@ -126,6 +128,7 @@ public function test_it_uses_default_sender_email_if_blank()
 
         $message = $this->sut->resolve(
             new Template(
+                null,
                 'Welcome, {{ user.name }}',
                 null,
                 new ParticipantListTemplate([new ParticipantTemplate(null, '{{ user.email }}')]),
@@ -163,6 +166,7 @@ public function test_it_resolves_message_with_multiple_templated_recipients()
 
         $message = $this->sut->resolve(
             new Template(
+                null,
                 'Welcome, {{ user.name }}',
                 new ParticipantTemplate(null, 'noreply@example.com'),
                 new ParticipantListTemplate([new ParticipantTemplate(null, '{{ user.email }}')]),
diff --git a/tests/Unit/Outstack/Enveloper/Templates/Loader/FilesystemLoaderTest.php b/tests/Unit/Outstack/Enveloper/Templates/Loader/FilesystemLoaderTest.php
index bbc18df..e67c6f1 100644
--- a/tests/Unit/Outstack/Enveloper/Templates/Loader/FilesystemLoaderTest.php
+++ b/tests/Unit/Outstack/Enveloper/Templates/Loader/FilesystemLoaderTest.php
@@ -71,6 +71,7 @@ public function test_finds_simplest_possible_template()
 
         $this->assertEquals(
             new Template(
+                null,
                 'Welcome, {{ user.handle }}',
                 null,
                 new ParticipantListTemplate([new ParticipantTemplate(null, '{{ user.email }}')]),
@@ -110,6 +111,7 @@ public function test_finds_template_with_attachment()
 
         $this->assertEquals(
             new Template(
+                null,
                 'Welcome, {{ user.handle }}',
                 null,
                 new ParticipantListTemplate([new ParticipantTemplate(null, '{{ user.email }}')]),
@@ -152,6 +154,7 @@ public function test_finds_template_with_attachment_iterator()
 
         $this->assertEquals(
             new Template(
+                null,
                 'Welcome, {{ user.handle }}',
                 null,
                 new ParticipantListTemplate([new ParticipantTemplate(null, '{{ user.email }}')]),
@@ -196,6 +199,7 @@ public function test_recipients_can_be_array_of_templated_name_and_email()
 
         $this->assertEquals(
             new Template(
+                null,
                 'Welcome, {{ user.handle }}',
                 new ParticipantTemplate(null, 'noreply@example.com'),
                 new ParticipantListTemplate([new ParticipantTemplate(null, '{{ user.email }}')]),
@@ -216,4 +220,71 @@ public function test_recipients_can_be_array_of_templated_name_and_email()
             $this->sut->find('new-user-welcome')
         );
     }
+
+    public function test_schema_is_loaded()
+    {
+        $meta = Yaml::dump([
+            'subject' => 'Welcome, {{ user.handle }}',
+            'from' => 'noreply@example.com',
+            'recipients' => [
+                'to' => [
+                    '{{ user.email }}'
+                ]
+            ],
+            'content' => [
+                'html' => 'new-user-welcome.html.twig'
+            ]
+        ]);
+
+        $schema = <<<SCHEMA
+{
+  "properties": {
+    "user": {
+      "type": "object",
+      "properties": {
+        "handle": {
+          "type": "string"
+        }
+      }
+    }
+  }
+}
+SCHEMA;
+
+
+        $html = '<!DOCTYPE html><html><body><p>Welcome, {{ user.handle }}.</p></body></html>';
+
+        $this->filesystem->write("new-user-welcome/new-user-welcome.html.twig", $html);
+        $this->filesystem->write("new-user-welcome/new-user-welcome.meta.yml", $meta);
+        $this->filesystem->write("new-user-welcome/new-user-welcome.schema.json", $schema);
+
+
+        $this->assertEquals(
+            new Template(
+                (object) [
+                    'properties' => (object) [
+                        'user' => (object) [
+                            'type' => 'object',
+                            'properties' => (object) [
+                                'handle' => (object) [
+                                    'type' => 'string'
+                                ]
+                            ]
+                        ]
+                    ]
+                ],
+                'Welcome, {{ user.handle }}',
+                new ParticipantTemplate(null, 'noreply@example.com'),
+                new ParticipantListTemplate([new ParticipantTemplate(null, '{{ user.email }}')]),
+                new ParticipantListTemplate([]),
+                new ParticipantListTemplate([]),
+                null,
+                null,
+                'new-user-welcome.html.twig',
+                $html,
+                new AttachmentListTemplate([])
+            ),
+            $this->sut->find('new-user-welcome')
+        );
+    }
 }
\ No newline at end of file
diff --git a/tests/data/templates/message-with-attachments/message-with-attachments.schema.json b/tests/data/templates/message-with-attachments/message-with-attachments.schema.json
new file mode 100644
index 0000000..d428925
--- /dev/null
+++ b/tests/data/templates/message-with-attachments/message-with-attachments.schema.json
@@ -0,0 +1,25 @@
+{
+  "$schema": "http://json-schema.org/draft-06/schema#",
+  "properties": {
+    "email": {
+      "type": "string",
+      "format": "email"
+    },
+    "attachments": {
+      "type": "array",
+      "items": {
+        "type": "object",
+        "properties": {
+          "contents": {
+            "type": "string",
+            "minLength": 1
+          },
+          "filename": {
+            "type": "string",
+            "minLength": 1
+          }
+        }
+      }
+    }
+  }
+}
\ No newline at end of file