Criminal landlords and letting agents who exploit tenants in London are to be "named and shamed" on an online database, the mayor has announced.
The site will provide details of any landlords and letting agents who have been prosecuted for housing offences in London boroughs.
Labour's Sadiq Khan said it would help "deter dishonest landlords and agents".
Conservative housing spokesman Andrew Boff said it was a "good idea... but misses the crux of the problem."
City Hall said the database, which will be published on the Greater London Authority website, will allow renters to check a prospective landlord before moving into a property.
People will also be able to use the site to report suspected criminal landlords and letting agents.
Once a conviction has reached its expiry date, the record on the database will be automatically deleted.
National Landlords Association CEO Richard Lambert said the site would "make it much easier for renters to find and avoid anyone who has been prosecuted for housing related crimes".
Not adequate steps
Mr Boff said it was "a good idea to pull together the already public information". However, he said it missed the "crux of the problem".
"The worst offenders operate outside the system and thrive because of the shortage of housing - a shortage that the mayor is not taking adequate steps to address," he said.
When it starts in the autumn, the site will only provide records for Camden, Newham, Brent, Southwark, Kingston and Sutton.
Other boroughs will be added in 2018, City Hall said.