diff --git a/src/io/userapp/client/IUserAppAPI.java b/src/io/userapp/client/IUserAppAPI.java
new file mode 100644
index 0000000..17d6180
--- /dev/null
+++ b/src/io/userapp/client/IUserAppAPI.java
@@ -0,0 +1,26 @@
+package io.userapp.client;
+
+import io.userapp.client.exceptions.InvalidMethodException;
+import io.userapp.client.exceptions.InvalidServiceException;
+import io.userapp.client.exceptions.ServiceException;
+import io.userapp.client.exceptions.TransportException;
+import io.userapp.client.exceptions.UserAppException;
+
+public interface IUserAppAPI {
+
+	public void setOptions(UserApp.ClientOptions options);
+
+	public UserApp.ClientOptions getOptions();
+
+	/* Set the API method */
+	public IUserAppAPI method(String name);
+
+	/* Add an input parameter */
+	public IUserAppAPI parameter(String name, Object value);
+
+	/* Perform the API call */
+	public UserApp.Result call() throws UserAppException,
+			TransportException, ServiceException, InvalidServiceException,
+			InvalidMethodException;
+
+}
\ No newline at end of file
diff --git a/src/io/userapp/client/UserApp.java b/src/io/userapp/client/UserApp.java
index 0777134..ce728ab 100644
--- a/src/io/userapp/client/UserApp.java
+++ b/src/io/userapp/client/UserApp.java
@@ -187,7 +187,7 @@ public boolean toBoolean() {
 	}
 
 	/* API wrapper class */
-	public static class API {
+	public static class API implements IUserAppAPI {
 		private UserApp.ClientOptions options;
 		RestfulContext restfulContext = new RestfulContext();
 		URI serviceUrl;
@@ -205,7 +205,7 @@ public API(String appId, String token) {
 		public API(UserApp.ClientOptions options) {
 			this.setOptions(options);
 		}
-		
+
 		public void setOptions(UserApp.ClientOptions options) {
 			this.options = options;
 			this.restfulContext.setBasicAuthenticationCredentials(new UserCredentials(
@@ -215,20 +215,20 @@ public void setOptions(UserApp.ClientOptions options) {
 				String.format("%s://%s/v%d/", (this.options.secure ? "https" : "http"), this.options.baseAddress, this.options.version)
 			);
 		}
-		
+
 		public UserApp.ClientOptions getOptions() {
 			return this.options;
 		}
 		
 		/* Set the API method */
-		public UserApp.API method(String name) {
+		public IUserAppAPI method(String name) {
 			this.methodName = name;
 			this.parameters.clear();
 			return this;
 		}
 		
 		/* Add an input parameter */
-		public UserApp.API parameter(String name, Object value) {
+		public IUserAppAPI parameter(String name, Object value) {
 			this.parameters.add(new UserApp.Parameter(name, value));
 			return this; 
 		}
diff --git a/src/io/userapp/client/demo/Demo.java b/src/io/userapp/client/demo/Demo.java
index 8cd7e89..1c55b41 100644
--- a/src/io/userapp/client/demo/Demo.java
+++ b/src/io/userapp/client/demo/Demo.java
@@ -2,6 +2,7 @@
 
 import java.util.ArrayList;
 
+import io.userapp.client.IUserAppAPI;
 import io.userapp.client.UserApp;
 import io.userapp.client.exceptions.*;
 
@@ -22,7 +23,7 @@ public static void main(String[] args) {
 			options.throwErrors = false;
 			UserApp.API api = new UserApp.API(options);*/
 			
-			UserApp.API api = new UserApp.API("YOUR-USERAPP-APP-ID");
+			IUserAppAPI api = new UserApp.API("YOUR-USERAPP-APP-ID");
 			
 			/*
 			 * Sign up a new user