Supported inputs: .xlsx, .xlsm, .xls (legacy Excel 97-2003).

Output:

• CSV — UTF-8 with BOM (opens correctly in Excel without garbled characters).
• JSON (array of objects) — first row used as keys; best for code consumption.
• JSON (array of arrays) — preserves rows as positional arrays; no key inference.

If the workbook has multiple sheets and you don't specify one, all sheets are exported and bundled as a ZIP. Formulas are evaluated to their cached values (Excel stores both); if a formula has never been recalculated, the export shows the stale cached value.