It depends what you mean by 'on-line version', and how exotic the rules of your variant are. On chessvariants.com there is a general system for playing custom-designed chess variants over the internet called Game Courier. (Correspondence chess only, though, no real-time clocks.) The Play-Test Applet there can be used to facilitate defining the variant, or can be used as a simple computer opponent.
Help building chess variant
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Hi, I am playing around with a new chess variant. I was wondering if there was anyone, or any resources which could help me build an online version of the game. Any feedback is welcome.