How to do it
- Drop the .xlsx onto the editor. The first sheet is read; there is nothing to configure.
- Look at what arrived. Dates and numbers are written as their stored values, which is occasionally not what the cell appeared to say.
- Export as TSV, choosing the line ending and whether to include a byte order mark.
What usually goes wrong
Formatted versus stored values
A cell displaying 12.3% stores 0.123. What you get is the stored value, because that is the one that survives arithmetic.
Merged cells
A merged block belongs to its top-left cell; the rest of the block arrives empty. Worth checking before assuming a column is broken.
Password protection
An encrypted workbook cannot be opened in the browser. There is no server here to send it to, which is a feature and, in this one case, a limit.
Only the first sheet is read. If you need another, save it as its own workbook first.