diff --git a/lib/cloudevent.js b/lib/cloudevent.js
index 973049c..d7214d2 100644
--- a/lib/cloudevent.js
+++ b/lib/cloudevent.js
@@ -16,6 +16,10 @@ function Cloudevent(_spec, _formatter){
  * To format the payload using the formatter
  */
 Cloudevent.prototype.format = function(){
+  // Check the constraints
+  this.spec.check();
+
+  // Then, format
   return this.formatter.format(this.spec.payload);
 }
 
diff --git a/lib/specs/spec_0_2.js b/lib/specs/spec_0_2.js
index de8fed8..01b53a8 100644
--- a/lib/specs/spec_0_2.js
+++ b/lib/specs/spec_0_2.js
@@ -7,6 +7,13 @@ function Spec_0_2(){
   };
 }
 
+/*
+ * Check the spec constraints.
+ */
+Spec_0_2.prototype.check = function(){
+
+}
+
 Spec_0_2.prototype.type = function(_type){
   this.payload['type'] = _type;
   return this;