Reads .xlsx workbooks in the Worker with the in-house ZIP reader and XML parser (no SheetJS): workbook and sheet relationships, shared and inline strings with rich-text runs, numbers, booleans, error cells, formulas (cached values or the formula text), date serials resolved through cell number formats in the 1900 or 1904 system, merged ranges and hidden sheets. Convert every sheet or one sheet to JSON (row objects keyed by the header or plain arrays), CSV/TSV with formula-injection guarding, HTML tables with merged cells, XML or Markdown, with a live table preview and a summary of every sheet. Everything runs locally.