Intelligentgiving.com uses 43 criteria to build up ratings in four areas, including quality of reporting and whether the charity's top salary is disclosed.
The better the score, the bigger the smile that is displayed on the charity's record.
So far, 550 of the 1,400 featured charities on the site are profiled in detail using these criteria.
The site is the brainchild of journalist and web consultant David Pitchford (Third Sector, 8 March). "We want to highlight the charities that have done well," he said.
"It's quite hard to find ones that have done badly - it just isn't designed for it."
The site has been funded by e-business entrepreneur Peter Heywood and Beyond the Barn, a grant-giver.