Fry, host of quiz show "QI," said the contest at Spellathon.net challenges users who obtain at least $24 in sponsorships by Feb. 1 to correctly spell 50 words backward using the site's games, the Coventry Telegraph reported Thursday.
Qualifying players will then have 15 minutes to spell the longest run of words with the letters in reverse order.
"I'm greatly looking forward to competing against the world in this extremely tricky challenge," Fry said. "This is just about the best integration of imagination, education, technology inclusiveness and fun that I've ever encountered. Very proud to have been involved in it."
Fry said the event will raise money for the learning disability charity Mencap as well as the schools and universities of participating students.