Valve has instituted a US$100 (AU$98) fee for listing a game on Steam Greenlight in a bid to cut the number of joke listings on the service.

“There is unfortunately a significant amount of noise and clutter being submitted, either as a joke or by fans not fully understanding the purpose of Greenlight,” posted Valve on its community blog.

The fee will go to charity Childs Play as Valve had no interest in profiting from the service, it said.

Those with games already listed would not need to retroactively pay the fee.

A second change to the system was also announced: a “smaller, more manageable” list of games not yet rated would be shown to the user – a mix of popular and new games.

“In the end, we’re very interested in maintaining an environment that is fair and beneficial to everyone involved, and one that fun and rewarding to join,” said Valve.

The Greenlight service has seen over 700 submissions since it launched on August 31.