diff --git a/README.md b/README.md
index 0431451..a4656ce 100644
--- a/README.md
+++ b/README.md
@@ -70,7 +70,9 @@ String Cloudevent.toString()
 
 ```
 
-## `Formatter` class
+## `Formatter` classes
+
+Every formatter class must implement these methods to work properly.
 
 ```js
 
@@ -86,6 +88,19 @@ String Formatter.toString(payload)
 
 ```
 
+## `Spec` classes
+
+Every Spec class must implement these methods to work properly.
+
+```js
+
+/*
+ * Check the spec constraints, throwing an error if do not pass.
+ */
+Spec.check()
+
+```
+
 # How to use
 
 The `Cloudevent` constructor arguments.
diff --git a/lib/specs/spec_0_1.js b/lib/specs/spec_0_1.js
index 3b4e657..3d87770 100644
--- a/lib/specs/spec_0_1.js
+++ b/lib/specs/spec_0_1.js
@@ -19,6 +19,15 @@ function Spec_0_1(_caller){
   }
 }
 
+/*
+ * Check the constraints.
+ *
+ * throw an error if do not pass.
+ */
+Spec_0_1.prototype.check = function() {
+
+}
+
 Spec_0_1.prototype.type = function(_type){
   this.payload['eventType'] = _type;
   return this;