Does the landlord have to keep the place liveable?
Answered for: New York
§ 235-b. Warranty of habitability. 1. In every written or oral lease or rental agreement for residential premises the landlord or lessor shall be deemed to covenant and warrant that the premises so leased or rented and all areas used in connection therewith in common with other tenants or residents are fit for human habitation and for the uses reasonably intended by the parties and that the occupants of such premises shall not be subjected to any conditions which would be dangerous, hazardous or detrimental to their life, health or safety. When any such condition has been caused by the misconduct of the tenant or lessee or persons under his direction or control, it shall not constitute a breach of such covenants and warranties. 2. Any agreement by a lessee or tenant of a dwelling waiving or modifying his rights as set forth in this section shall be void as contrary to public policy. 3. In determining the amount of damages sustained by a tenant as a result of a breach of the warranty set forth in the section, the court; (a) need not require any expert testimony; and [...]
Every residential lease in New York, written or oral, automatically includes the landlord's promise that the home and the shared areas are fit to live in and free of conditions dangerous to life, health or safety. A tenant cannot be made to sign that promise away, and a court awarding damages for a breach need not require expert testimony.
This answer is true in New York and nowhere else on this site. Another jurisdiction is another answer, or an honest gap: see what has been read for New York.