The contract name 'IMetadataExchange' could not be found in the list of contracts implemented by the service

The contract name 'IMetadataExchange' could not be found in the list of contracts implemented by the service HelloWorld.  Add a ServiceMetadataBehavior to the configuration file or to the ServiceHost directly to enable support for this contract.

This error occurs when we define a servicebehavior and did not attach the behavior to the service name configuration.

If your configuration looks like below and when you try to run the host, you will get the error specified above.

<?xml version="1.0" encoding="utf-8" ?>

<configuration>

      <system.serviceModel>

            <services>

                  <service name="HelloWorldService.HelloWorld">

                        <endpoint contract="HelloWorldService.IHelloWorld" address="HelloWorld" binding="basicHttpBinding"></endpoint>

                        <endpoint contract="IMetadataExchange" address="Mex" binding="mexHttpBinding"></endpoint>

                        <host>

                              <baseAddresses>

                                    <add baseAddress="http://localhost:8000"/>

                              </baseAddresses>

                        </host>

                  </service>

            </services>

            <behaviors>

                  <serviceBehaviors>

                        <behavior name="MyServiceBehavior">

                              <serviceMetadata httpGetEnabled="true"/>

                        </behavior>

                  </serviceBehaviors>

            </behaviors>

      </system.serviceModel>

</configuration>

The solution is as below in this case (Add the behaviorConfiguration in the service section):

<?xml version="1.0" encoding="utf-8" ?>

<configuration>

      <system.serviceModel>

            <services>

                  <service name="HelloWorldService.HelloWorld" behaviorConfiguration="MyServiceBehavior">

                        <endpoint contract="HelloWorldService.IHelloWorld" address="HelloWorld" binding="basicHttpBinding"></endpoint>

                        <endpoint contract="IMetadataExchange" address="Mex" binding="mexHttpBinding"></endpoint>

                        <host>

                              <baseAddresses>

                                    <add baseAddress="http://localhost:8000"/>

                              </baseAddresses>

                        </host>

                  </service>

            </services>

            <behaviors>

                  <serviceBehaviors>

                        <behavior name="MyServiceBehavior">

                              <serviceMetadata httpGetEnabled="true"/>

                        </behavior>

                  </serviceBehaviors>

            </behaviors>

      </system.serviceModel>

</configuration>