The accounts and governing documents of the top 300 charities have been placed online by the Charity Commission, enabling the public to instantly scrutinise them.
More than £10bn of charitable income can be viewed through the commission's web site.
The move is part of the commission's drive to improve the sector's transparency and accountability following the Private Action, Public Benefit report last year.
The regulator says that by 2006 all charity accounts and governing documents will be able to be viewed online.
Chief charity commissioner, John Stoker, said: "One of our aims is to increase public confidence and trust in charities. Our quest to make information available on all charities at the click of a button should help the public and funders make more informed decisions about which charities to support."
As part of its e-business strategy, the commission has also enabled charities to file their accounts and new organisations to register as charities online.