Sythe isn't a Runescape private server, there is no webclient.
This might still work http://www.sythe.org/community-general/1529966-unofficial-syth******.html#post11941632
It's the Sythe unofficial RSPS
Sythe has a RSPS:
http://www.sythe.org/community-general/1529966-unofficial-syth******.html#post11941632
You are, however, correct that there is no webclient.

