diff --git a/lib/API/Endpoints/CustomFields.php b/lib/API/Endpoints/CustomFields.php
index 5bdfcc4502..1dcfa908b4 100644
--- a/lib/API/Endpoints/CustomFields.php
+++ b/lib/API/Endpoints/CustomFields.php
@@ -1,34 +1,32 @@
 <?php
 namespace MailPoet\API\Endpoints;
-
+use \MailPoet\API\Endpoint as APIEndpoint;
+use \MailPoet\API\Error as APIError;
 use \MailPoet\Models\CustomField;
 
 if(!defined('ABSPATH')) exit;
 
-class CustomFields {
-  function __construct() {
-  }
-
+class CustomFields extends APIEndpoint {
   function getAll() {
     $collection = CustomField::findMany();
     $custom_fields = array_map(function($custom_field) {
       return $custom_field->asArray();
     }, $collection);
 
-    return $custom_fields;
+    return $this->successResponse($custom_fields);
   }
 
-  function delete($id) {
+  function delete($data = array()) {
+    $id = (isset($data['id']) ? (int)$data['id'] : null);
     $custom_field = CustomField::findOne($id);
-    if($custom_field === false or !$custom_field->id()) {
-      return array('result' => false);
+    if($custom_field === false) {
+      return $this->errorResponse(array(
+        APIError::NOT_FOUND => __('This custom field does not exist.')
+      ));
     } else {
       $custom_field->delete();
 
-      return array(
-        'result' => true,
-        'field' => $custom_field->asArray()
-      );
+      return $this->successResponse($custom_field->asArray());
     }
   }
 
@@ -37,24 +35,23 @@ class CustomFields {
     $errors = $custom_field->getErrors();
 
     if(!empty($errors)) {
-      return array(
-        'result' => false,
-        'errors' => $errors
-      );
+      return $this->badRequest($errors);
     } else {
-      return array(
-        'result' => true,
-        'field' => $custom_field->asArray()
+      return $this->successResponse(
+        CustomField::findOne($custom_field->id)->asArray()
       );
     }
   }
 
-  function get($id) {
+  function get($data = array()) {
+    $id = (isset($data['id']) ? (int)$data['id'] : null);
     $custom_field = CustomField::findOne($id);
     if($custom_field === false) {
-      return false;
+      return $this->errorResponse(array(
+        APIError::NOT_FOUND => __('This custom field does not exist.')
+      ));
     } else {
-      return $custom_field->asArray();
+      return $this->successResponse($custom_field->asArray());
     }
   }
 }
\ No newline at end of file
diff --git a/tests/unit/API/CustomFieldsTest.php b/tests/unit/API/CustomFieldsTest.php
index 4f646cb613..f0faec7d40 100644
--- a/tests/unit/API/CustomFieldsTest.php
+++ b/tests/unit/API/CustomFieldsTest.php
@@ -1,6 +1,7 @@
 <?php
 
 use \MailPoet\API\Endpoints\CustomFields;
+use \MailPoet\API\Response as APIResponse;
 use \MailPoet\Models\CustomField;
 
 class CustomFieldsTest extends MailPoetTest {
@@ -58,9 +59,10 @@ class CustomFieldsTest extends MailPoetTest {
   function testItCanGetAllCustomFields() {
     $router = new CustomFields();
     $response = $router->getAll();
-    expect($response)->count(count($this->custom_fields));
+    expect($response->status)->equals(APIResponse::STATUS_OK);
+    expect($response->data)->count(count($this->custom_fields));
 
-    foreach($response as $custom_field) {
+    foreach($response->data as $custom_field) {
       expect($custom_field['name'])->notEmpty();
       expect($custom_field['type'])->notEmpty();
       expect($custom_field['params'])->notEmpty();
@@ -72,14 +74,14 @@ class CustomFieldsTest extends MailPoetTest {
     $custom_field_id = $custom_field->id();
 
     $router = new CustomFields();
-    $response = $router->delete($custom_field_id);
-    expect($response['result'])->true();
+    $response = $router->delete(array('id' => $custom_field_id));
+    expect($response->status)->equals(APIResponse::STATUS_OK);
 
     $custom_field = CustomField::where('type', 'date')->findOne();
     expect($custom_field)->false();
 
-    $response = $router->delete($custom_field_id);
-    expect($response['result'])->false();
+    $response = $router->delete(array('id' => $custom_field_id));
+    expect($response->status)->equals(APIResponse::STATUS_NOT_FOUND);
   }
 
   function testItCanSaveACustomField() {
@@ -90,37 +92,37 @@ class CustomFieldsTest extends MailPoetTest {
 
     $router = new CustomFields();
     $response = $router->save($new_custom_field);
-    expect($response['result'])->true();
+    expect($response->status)->equals(APIResponse::STATUS_OK);
 
     // missing type
     $response = $router->save(array('name' => 'New custom field'));
-    expect($response['result'])->false();
-    expect($response['errors'][0])->equals('Please specify a type');
+    expect($response->status)->equals(APIResponse::STATUS_BAD_REQUEST);
+    expect($response->errors[0]['message'])->equals('Please specify a type');
 
     // missing name
     $response = $router->save(array('type' => 'text'));
-    expect($response['result'])->false();
-    expect($response['errors'][0])->equals('Please specify a name');
+    expect($response->status)->equals(APIResponse::STATUS_BAD_REQUEST);
+    expect($response->errors[0]['message'])->equals('Please specify a name');
 
     // missing data
     $response = $router->save();
-    expect($response['result'])->false();
-    expect($response['errors'][0])->equals('Please specify a name');
-    expect($response['errors'][1])->equals('Please specify a type');
+    expect($response->status)->equals(APIResponse::STATUS_BAD_REQUEST);
+    expect($response->errors[0]['message'])->equals('Please specify a name');
+    expect($response->errors[1]['message'])->equals('Please specify a type');
   }
 
   function testItCanGetACustomField() {
     $custom_field = CustomField::where('name', 'CF: text')->findOne();
 
     $router = new CustomFields();
-    $response = $router->get($custom_field->id());
-    expect($response)->notEmpty();
-    expect($response['name'])->equals('CF: text');
-    expect($response['type'])->equals('text');
-    expect($response['params'])->notEmpty();
+    $response = $router->get(array('id' => $custom_field->id()));
 
-    $response = $router->get('not_an_id');
-    expect($response)->false();
+    expect($response->data['name'])->equals('CF: text');
+    expect($response->data['type'])->equals('text');
+    expect($response->data['params'])->notEmpty();
+
+    $response = $router->get(array('id' => 'not_an_id'));
+    expect($response->status)->equals(APIResponse::STATUS_NOT_FOUND);
   }
 
   function _after() {
diff --git a/views/form/editor.html b/views/form/editor.html
index 416a057f8e..32b573fd98 100644
--- a/views/form/editor.html
+++ b/views/form/editor.html
@@ -282,9 +282,7 @@
           endpoint: 'customFields',
           action: 'getAll',
         }).done(function(response) {
-          if(response !== false) {
-            data.fields  = $.merge(response, data.fields);
-          }
+          data.fields  = $.merge(response.data, data.fields);
 
           // render toolbar
           jQuery('#mailpoet_toolbar_fields').html(template(data));
@@ -489,18 +487,6 @@
               action: 'saveEditor',
               data: form
             }).done(function(response) {
-              if(response.result === false) {
-                if(response.errors.length > 0) {
-                  MailPoet.Notice.error(response.errors.join('<br />'));
-                } else {
-                  MailPoet.Notice.error(
-                    "<%= __('An error occurred. Please reload the page and try again.') %>"
-                  );
-                }
-
-                return false;
-              }
-
               if(callback !== false) {
                 var message = null;
 
@@ -523,6 +509,13 @@
                   callback();
                 }
               }
+            }).fail(function(response) {
+              if (response.errors.length > 0) {
+                MailPoet.Notice.error(
+                  response.errors.map(function(error) { return error.message; }),
+                  { scroll: true }
+                );
+              }
             });
           }
         }
@@ -579,14 +572,21 @@
           MailPoet.Ajax.post({
             endpoint: 'customFields',
             action: 'get',
-            data: id
+            data: {
+              id: id
+            }
           }).done(function(response) {
-            if(response.result !== false) {
-              MailPoet.Modal.popup({
-                title: "<%= __('Edit field') %>",
-                template: $('#form_template_field_form').html(),
-                data: response
-              });
+            MailPoet.Modal.popup({
+              title: "<%= __('Edit field') %>",
+              template: $('#form_template_field_form').html(),
+              data: response.data
+            });
+          }).fail(function(response) {
+            if (response.errors.length > 0) {
+              MailPoet.Notice.error(
+                response.errors.map(function(error) { return error.message; }),
+                { scroll: true }
+              );
             }
           });
         });
@@ -603,22 +603,20 @@
             MailPoet.Ajax.post({
               endpoint: 'customFields',
               action: 'delete',
-              data: id
-            }).done(function(response) {
-              if(response.result === true) {
-                item.remove();
-
-                if(response.field !== undefined) {
-                  WysijaForm.removeBlock(response.field, function() {
-                    mailpoet_form_save(false);
-                  });
-                }
-
-                mailpoet_form_fields();
-                MailPoet.Notice.success(
-                  "<%= __('Removed custom field “"+name+"“') %>"
-                );
+              data: {
+                id: id
               }
+            }).done(function(response) {
+              item.remove();
+
+              WysijaForm.removeBlock(id, function() {
+                mailpoet_form_save(false);
+              });
+
+              mailpoet_form_fields();
+              MailPoet.Notice.success(
+                "<%= __('Removed custom field “"+name+"“') %>"
+              );
             });
           }
         });
diff --git a/views/form/templates/settings/field_form.hbs b/views/form/templates/settings/field_form.hbs
index 1ac51dea8e..d315e17508 100644
--- a/views/form/templates/settings/field_form.hbs
+++ b/views/form/templates/settings/field_form.hbs
@@ -78,32 +78,31 @@
           action: 'save',
           data: data
         }).done(function(response) {
-          if(response.result === true) {
-            // close popup
-            MailPoet.Modal.close();
+          // close popup
+          MailPoet.Modal.close();
 
-            if(WysijaForm.updateBlock(response.field) === true) {
-              // trigger save, if a block has been updated
-              mailpoet_form_save(false);
-            }
+          if(WysijaForm.updateBlock(response.data) === true) {
+            // trigger save, if a block has been updated
+            mailpoet_form_save(false);
+          }
 
-            mailpoet_form_fields();
+          mailpoet_form_fields();
 
-            if(data.id) {
-              MailPoet.Notice.success(
-                "<%= __('Updated custom field “"+data.name+"“') %>"
-              );
-            } else {
-              MailPoet.Notice.success(
-                "<%= __('Added custom field “"+data.name+"“') %>"
-              );
-            }
+          if(data.id) {
+            MailPoet.Notice.success(
+              "<%= __('Updated custom field “"+data.name+"“') %>"
+            );
           } else {
-            if(response.errors.length > 0) {
-              $(response.errors).each(function(i, error) {
-                MailPoet.Notice.error(error, {positionAfter: '#field_name'});
-              });
-            }
+            MailPoet.Notice.success(
+              "<%= __('Added custom field “"+data.name+"“') %>"
+            );
+          }
+        }).fail(function(response) {
+          if(response.errors.length > 0) {
+            MailPoet.Notice.error(
+              response.errors.map(function(error) { return error.message; }),
+              { positionAfter: '#field_name' }
+            );
           }
         });
         return false;