To run by command line

    vnu

To validate a file to an instance of the servlet (system tomcat, system jetty, or vnu standalone server)

    vnu-client myFile.html

To run the standalone server

    vnu-server

To test a file which URL is on localhost (or 127.0.0.1 or alike), use your hostname instead of localhost.
See https://github.com/validator/validator/issues/1451#issuecomment-1290417602