Error: no header row with unit, rent
Rename the columns to Unit and Current Rent (or Rent) and run again.
Rows to check: no market rent
Add a Market Rent column; until then current rent is used, so loss-to-lease reads zero for that unit.
Dates read the wrong way round
Add --us-dates for month-first dates such as 03/04/2026.
Claude does not use the skill
Check it is switched on in Settings → Capabilities → Skills, then name it in your message.
The script says a column is missing
Rename your header to one of the names in README, or say the mapping in your message.
Code execution is off
Skills with scripts need code execution enabled in Claude.ai settings.
FAQ
Which rent rolls work? Any CSV or Excel with one row per unit and columns for unit and current rent; market rent, status, tenant, lease dates, sq ft and balance are used when present.
How is a vacant unit found? From the status column (vacant, notice, model). With no status column, a unit with no tenant name is vacant.
Is this investment advice? No. It summarises the figures in your rent roll. Check them against leases and the ledger.
What is mark-to-market upside? Loss-to-lease times twelve: the yearly rent gained if every occupied unit were at market rent.