diff --git a/extensions/mistral/static/mistral/js/mistral.workbook.models.js b/extensions/mistral/static/mistral/js/mistral.workbook.models.js
index 53715dd..1d0a103 100644
--- a/extensions/mistral/static/mistral/js/mistral.workbook.models.js
+++ b/extensions/mistral/static/mistral/js/mistral.workbook.models.js
@@ -559,7 +559,12 @@
                 'index': 0,
                 'panelIndex': 0,
                 'row': 0
-              }
+              },
+              '@constraints': [
+                function(value) {
+                  return value !== 'workbook1' ? true : 'The sample validation failure.';
+                }
+              ]
             })
           },
           'description': {
diff --git a/merlin/static/merlin/js/merlin.directives.js b/merlin/static/merlin/js/merlin.directives.js
index 002e655..8d53ca8 100644
--- a/merlin/static/merlin/js/merlin.directives.js
+++ b/merlin/static/merlin/js/merlin.directives.js
@@ -112,6 +112,36 @@
         }
       }
     })
+    .directive('validatableWith', function($parse) {
+      return {
+        restrict: 'A',
+        require: 'ngModel',
+        link: function(scope, element, attrs, ctrl) {
+          var model;
+          if ( attrs.validatableWith ) {
+            model = $parse(attrs.validatableWith)(scope);
+            scope.error = '';
+            model.setValidatable && model.setValidatable(true);
+            model.on && model.on('validation', function(result) {
+              var isValid = (result == 'succeeded'),
+                baseMessage = '';
+              // (FIXME): hack until Barricade supports validation of empty required entries
+              if ( !model.get() && model.isRequired() ) {
+                isValid = false;
+                baseMessage = 'This field is required.'
+              }
+              ctrl.$setValidity('barricade', isValid);
+              scope.error = model.hasError() ? model.getError() : baseMessage;
+            });
+            ctrl.$formatters.push(function(modelValue) {
+              return modelValue === undefined ?
+                ( ctrl.$isEmpty(ctrl.$viewValue) ? undefined : ctrl.$viewValue ) :
+                modelValue;
+            });
+          }
+        }
+      }
+    })
     .directive('typedField', ['$compile', 'merlin.templates',
       function($compile, templates) {
         function updateAutoCompletionDirective(template) {
diff --git a/merlin/static/merlin/js/merlin.field.models.js b/merlin/static/merlin/js/merlin.field.models.js
index 47ae295..dbc393b 100644
--- a/merlin/static/merlin/js/merlin.field.models.js
+++ b/merlin/static/merlin/js/merlin.field.models.js
@@ -32,11 +32,18 @@
       });
 
       var modelMixin = Barricade.Blueprint.create(function(type) {
+        var isValid = true,
+          isValidatable = false;
         this.value = function() {
           if ( !arguments.length ) {
-            return this.get();
+            if ( isValidatable ) {
+              return isValid ? this.get() : undefined;
+            } else {
+              return this.get();
+            }
           } else {
             this.set(arguments[0]);
+            isValid = !this.hasError();
           }
         };
         this.id = utils.getNewId();
@@ -45,6 +52,10 @@
           return type;
         };
 
+        this.setValidatable = function(validatable) {
+          isValidatable = validatable;
+        };
+
         this.setType = function(_type) {
           type = _type;
         };
diff --git a/merlin/static/merlin/scss/merlin.scss b/merlin/static/merlin/scss/merlin.scss
index b1b842a..b33a08c 100644
--- a/merlin/static/merlin/scss/merlin.scss
+++ b/merlin/static/merlin/scss/merlin.scss
@@ -54,8 +54,13 @@
   }
 }
 
-editable .fa-pencil {
-  color: black;
+editable {
+  .fa-pencil {
+    color: black;
+  }
+  button:disabled {
+    color: gray;
+  }
 }
 
 .section {
diff --git a/merlin/static/merlin/templates/editable.html b/merlin/static/merlin/templates/editable.html
index 06bdd31..7d8dd91 100644
--- a/merlin/static/merlin/templates/editable.html
+++ b/merlin/static/merlin/templates/editable.html
@@ -5,6 +5,6 @@
 </span>
 <span ng-show="isEdited">
   <input type="text" ng-model="editableValue" show-focus="isEdited">
-  <button ng-click="accept()"><i class="fa fa-check"></i></button>
+  <button ng-click="accept()" ng-disabled="!editableValue"><i class="fa fa-check"></i></button>
   <button ng-click="reject()"><i class="fa fa-close"></i></button>
 </span>
diff --git a/merlin/static/merlin/templates/fields/number.html b/merlin/static/merlin/templates/fields/number.html
index 2b53f39..fbcc2b2 100644
--- a/merlin/static/merlin/templates/fields/number.html
+++ b/merlin/static/merlin/templates/fields/number.html
@@ -3,5 +3,6 @@
   <label for="elem-{$ $id $}">{$ value.title() $}</label>
   <input type="number" class="form-control" id="elem-{$ $id $}"
          ng-model="value.value" ng-model-options="{ getterSetter: true }"
-         autocompletable="true">
+         autocompletable="true" validatable-with="value">
+  <div ng-show="error" class="alert alert-danger">{$ error $}</div>
 </div>
diff --git a/merlin/static/merlin/templates/fields/string.html b/merlin/static/merlin/templates/fields/string.html
index e738076..b526869 100644
--- a/merlin/static/merlin/templates/fields/string.html
+++ b/merlin/static/merlin/templates/fields/string.html
@@ -2,5 +2,6 @@
   <label for="elem-{$ $id $}">{$ value.title() $}</label>
   <input type="text" class="form-control" id="elem-{$ $id $}"
          ng-model="value.value" ng-model-options="{ getterSetter: true }"
-         autocompletable="true">
+         autocompletable="true" validatable-with="value">
+  <div ng-show="error" class="alert alert-danger">{$ error $}</div>
 </div>
diff --git a/merlin/static/merlin/templates/fields/text.html b/merlin/static/merlin/templates/fields/text.html
index b961209..24173c3 100644
--- a/merlin/static/merlin/templates/fields/text.html
+++ b/merlin/static/merlin/templates/fields/text.html
@@ -2,5 +2,6 @@
   <label for="elem-{$ $id $}">{$ value.title() $}</label>
   <textarea class="form-control" id="elem-{$ $id $}"
             ng-model="value.value" ng-model-options="{ getterSetter: true }"
-            autocompletable="true"></textarea>
+            autocompletable="true" validatable-with="value"></textarea>
+  <div ng-show="error" class="alert alert-danger">{$ error $}</div>
 </div>
diff --git a/merlin/test/js/directivesSpec.js b/merlin/test/js/directivesSpec.js
index 3d8ca23..fd8fcc4 100644
--- a/merlin/test/js/directivesSpec.js
+++ b/merlin/test/js/directivesSpec.js
@@ -347,4 +347,83 @@ describe('merlin directives', function() {
     });
 
   });
+
+  describe("'validatable'", function() {
+    var fields;
+
+    beforeEach(inject(function($injector) {
+      fields = $injector.get('merlin.field.models');
+    }));
+
+    describe('working with the @constraints property:', function() {
+      var model, elt,
+        goodValue = 'allowedValue',
+        badValue = 'restrictedValue',
+        errorMessage = 'Wrong value provided';
+      beforeEach(function() {
+        var modelClass = fields.string.extend({}, {
+          '@constraints': [
+            function(value) {
+              return value !== badValue ? true : errorMessage;
+            }
+          ]
+        });
+        $scope.model = modelClass.create();
+        elt = $compile('<form name="form"><input name="model" type="text" ' +
+          'ng-model="model.value" ng-model-options="{ getterSetter: true }" ' +
+          'validatable-with="model"></form>')($scope);
+      });
+
+      describe('any valid value', function() {
+        beforeEach(function() {
+          $scope.form.model.$setViewValue(goodValue);
+          $scope.$digest();
+        });
+
+        it('is allowed to be entered', function() {
+          expect($scope.form.model.$viewValue).toEqual(goodValue);
+        });
+
+        it('is propagated into the model', function() {
+          expect($scope.model.value()).toEqual(goodValue);
+        });
+
+        it('does not cause the input to be marked as erroneous', function() {
+          expect(elt.find('input').hasClass('ng-valid')).toBe(true);
+        });
+
+        it('sets error message on scope to an empty string', function() {
+          expect($scope.error).toEqual('');
+        });
+      });
+
+      describe('any invalid value', function() {
+        beforeEach(function() {
+          $scope.form.model.$setViewValue(badValue);
+          $scope.$digest();
+        });
+
+        it('is allowed to be entered', function() {
+          expect($scope.form.model.$viewValue).toEqual(badValue);
+        });
+
+        it('is not propagated into the model', function() {
+          expect($scope.model.value()).toBe(undefined);
+        });
+
+        it('causes the input to be marked as erroneous', function() {
+          expect(elt.find('input').hasClass('ng-invalid')).toBe(true);
+        });
+
+        it('exposes error message in the parent scope', function() {
+          expect($scope.error).toEqual(errorMessage);
+        })
+      });
+    });
+
+    describe('working with the @required property', function() {
+      // TODO: fill in once validation of @required fields changes in Barricade
+    });
+  });
+
 });