Harvard Law School researchers have launched a Web page to test China's Internet firewall, allowing visitors to suggest sites to be tested.
Ben Adelman, a co-author of the project, said it aimed to make clear which sites were being blocked, as most governments and institutions that used filtering software did not list blocked sites.
The researchers hope to publish their findings in the next few months, and expect to list more than 1,000 blocked sites, of more than 60,000 tested.
He said the process compared unfavourably with customs inspections, where travellers were told clearly what goods were banned. 'That enforces a kind of transparency. The government can't cheat all that much because they have to tell people what is prohibited,' he said.
'Our goal then is to impose the transparency of the ordinary world, of the real world of customs inspectors and police. By letting the world know what is filtered and what is not filtered.'
Mr Adelman and co-author Jonathan Zittrain recently released a similar study of Saudi Arabia's Web filtering. Other countries might be looked at after China, including Singapore, Vietnam and the United Arab Emirates, Mr Adelman said.