Jane Jacobs (1961) theorized that four urban form conditions, namely, mixed use, short block, aged buildings and density, are indispensable for the ‘exuberant diversity’ and conducive to, or perhaps even determinant of, the success of a city district. Jacobs’ theory has been used widely as a reference point in case study research and policy and design prescriptions. We found five studies that attempted to test it more formally, using various performance indicators such as mobile phone activities, walking, crime and mortality. Their findings were inconsistent and unable to settle theoretical controversies. Questions remained as what performance indicators are most strongly associated with her urban form conditions? Are these conditions independently associated with desired outcomes or in combination and what are the interaction effects? Our study aimed to test Jacobs’ theory that urban form conditions contribute to the vitality and success of city districts. Jacobs’ urban form conditions were measured using GIS data for each of Hong Kong’s Tertiary Planning Unit. Performance outcomes were gauged using a combination of ‘new urban data’, comprising Twitter activities, sentiment tones and Point-Of-Interest (POI), and ‘traditional data’, comprising walking commute, employment and mortality. Urban context, income and demographic indicators were used as controls in fitting spatial regression models to predict measures of performances based on urban conditions. Results showed that Jacobs’ urban form conditions contribute positively to ‘vitality’ indicators such as the density of tweets, walking trips and POI, but not with ‘failure and success’ indicators such as expressed sentiment on Twitter, employment, or mortality. Out findings suggest that her theory largely hold for Hong Kong, except that dwelling density should be substituted by building density, whilst tall buildings associated positively with desirable outcomes, contrary to Jacobs’ observation in the American context. More generally, we demonstrate how new urban data can be used to evaluate classic planning theories at scale.