Extract data from an .xlsx spreadsheet: send the bytes directly or a JSON body with a public {url}. Returns each sheet as rows (array-of-arrays) with its name and used range, plus workbook metadata. Query: sheet (name or 0-based index) for a single sheet, headers=true for array-of-objects. Formula cells return their cached computed value. Capped at 500000 cells. Max 10 MB.