Homes have been added to My NHS, part the NHS Choices site, allowing users to leave ratings and reviews to help other people assess services.
Each care home is scored on its level of safety, staff turnover and food hygiene, among other standards.
The National Care Association said if information was not up to date, it could be "unfair" to care providers.
On the website, a database can be searched using a postcode, region or home name to check on facilities with or without nursing.
People can access:
Health Minister Alistair Burt said:  "We know how difficult important decisions about care for a loved one can be - this is a victory for those who are worried about care - with a click of a button the public will be able to make an informed choice about care and make those difficult decisions easier.
"This data will show clearly the difference in quality across care homes and will help drive up standards by highlighting poor performers which will mean they have to shape up their services or lose out."
Nadra Ahmed, chair of the National Care Association, which represents independent care sector providers, said the move could help people "answer some of the questions" they may have about care.
But she warned that if the "snapshot" of the provider's rating or profile on the site was not regularly updated it could disadvantage those who improve their service.
"I don't know how [improvements] would be indicated... especially if that report is not going to be reviewed for a period of time, which would be unfair."
She added: "Nothing beats actually going to see a service for yourself. If you think that it's good [but the website] says there's something that's not quite right, don't let it put you off.
"When you look at the website you know that responsible services who may have an inadequate rating will be working towards making that better."
The performance of every care home in England can now be compared on an NHS website.