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New tool helps mistreated tenants demystify building ownership uses an algorithm built on NYC open data to map property ownership across the city

A new online tool will make it easier for tenants facing harassment and negligent landlords to find out the important building ownership information they need to know.

The tool, called, primarily uses data from the Department of Housing Preservation and Development’s multiple dwelling registrations to show users the business entities, business addresses, and people associated with the property. also shows users the property’s number of total and open violations as well as the eviction rate for the building in the previous year.

The tool cuts through the opaque layers of building ownership in New York—think limited liability corporations—and helps tenants get the information they need to either hold their landlord accountable or collectively organize with other tenants suffering the same abuses across buildings. is just one site under the banner, a suite of internet-based programs that aim to supply New Yorkers with the tools that will help them fight wrongful displacement and gentrification in their neighborhoods. is a Brookyn-based advocacy nonprofit providing a free service that soft launched in May 2018. Since then, users have run over 20,000 searches on the site.

A screenshot from

A press release clarifies how the tools can help tenants:

Combining the data from Who Owns What with aggregated data from’s other tool, the Tenant App for repairs and harassment, the organization intends to facilitate collective action with many tenants in a building or in different buildings across a landlord’s portfolio. In partnership with tenant organizing efforts, legal aid providers, and local elected officials, has already begun the formation of group cases against landlords with clear patterns of neglect, harassment, evictions, and deregulation of affordable units. has won the support of Councilwoman Helen Rosenthal who represents the Upper West Side. “Who Owns What is an extremely helpful new tool, particularly for tenants who do not have an attorney or other ways to track down vital information,” said Rosenthal. “With its user friendly format, WoW increases transparency and gives tenants a vital way to begin to address housing issues they may be facing.” Now that’s a tool worth having.