uuh yes, the syntax checker. It was a part of the previous version of the EDIFACTORY site. Currently, it is not available. But heads up, the tool isn't lost. I just need some more time to reanimate this tool in the new environment.
Maybe it will become a totally new tool because the site now is based on a database, not on XML files any longer (while the database is filled with the data from out XML tarballs).
Lets see... (and wait)
You may want to try a prerelease of the Syntax Checker.