Numbers, and the ones that only look like numbers
With Numbers as numbers ticked, numeric fields are written as real numbers so Excel can sum and sort them. Anything starting with a zero followed by a digit is left as text on purpose — postcodes, part numbers and phone numbers lose their meaning the moment 007 becomes 7, and that is the single most common way a CSV import quietly corrupts a dataset.
Untick it and every cell is written as text, which is the safe choice when the data is going somewhere that will parse it again.
Delimiters
Detection tries comma, semicolon, tab and pipe, and picks whichever splits the first line into the most fields. Semicolons are usual in European exports, where the comma is the decimal separator. Override it if your data is unusual enough to fool the guess.
Frequently asked questions
Is my data uploaded anywhere?
No. The workbook is built in your browser and saved straight to your downloads folder. Nothing is sent anywhere.
Will Excel open the file without complaining?
Yes — it is a standard .xlsx, the same format Excel itself writes. It opens in Excel, LibreOffice, Numbers and Google Sheets.
Can I put several CSVs into one workbook as separate sheets?
Not yet — one CSV makes one sheet. Convert them separately for now.
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