If you’re using Eclipse, just have your WSDL in a .wsdl file, eclipse will validate it automatically.
From the Doc
The WSDL validator handles validation
according to the 4 step process
defined above. Steps 1 and 2 are both
delegated to Apache Xerces (and XML
parser). Step 3 is handled by the WSDL
validator and any extension namespace
validators (more on extensions below).
Step 4 is handled by any declared
custom validators (more on this below
as well). Each step must pass in order
for the next step to run.