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Open an .xlsx or a .csv and it converts to the other. Nothing is uploaded: an .xlsx is a ZIP of XML and the browser already has a ZIP engine.
1. Open a file
Drop a .xlsx or .csv here, or click to chooseNothing is uploaded; it is opened inside this tab
2. What is in it
3. Save it
Open an .xlsx or a .csv and save it as the other.
The classic way a spreadsheet tool destroys data is by being clever: it sees
007 and stores 7, sees SW1A 1AA and mangles it, sees a
date and reformats it to whatever locale it feels like. Anything with a leading
zero is treated as text here, because a value that starts with a zero is nearly
always an identifier (an account, a phone number, a postcode) and
never a quantity.
CSV is read with its quoting rules honoured, so a comma inside a quoted field
stays inside that field. The delimiter is detected rather than assumed, so the
semicolon-separated exports that most of Europe produces work without a setting.
Is this actually private?
Nothing is uploaded. Static page, no endpoint, no account. An .xlsx is a ZIP of XML and the browser already has a ZIP engine, so this half needs no download at all.
Values, not formulas. A cell containing a formula exports the value it last calculated, which is what the spreadsheet was showing. Formulas themselves are not carried into CSV, because CSV has no way to hold one.
A cell whose text starts with = or @ gets a leading apostrophe on the way out. Those characters make a spreadsheet treat the text as a live formula when the CSV is reopened, which is how a booby-trapped file can run something on the next person to open it. The apostrophe keeps it as the text it was. Ordinary numbers, including negative ones, are left exactly as they are.
Formatting is not carried across. Colours, fonts, column widths, merged cells, charts and conditional formatting are presentation, and CSV has none of it. Going the other way, a CSV becomes a plain grid.
Dates come out as the file stored them. Excel keeps a date as a number with a display format attached; without applying that format the underlying number is what you get. Reformatting dates by guessing is how tools turn 03/04 into the wrong month, so this does not guess.
Every sheet is read. Pick which one to export; CSV holds exactly one grid, so one sheet at a time. Exporting to .xlsx keeps them all.
Big files are real work. Everything is held in the tab, so a spreadsheet with hundreds of thousands of rows will be slow on a phone.
Nothing here is for sale, nothing is tracked, and there is no account to make.
If something saved you an hour: 83TQcTwusSQ4WKbPQE5osrF3cR4GWe2zmcNWeozK6BSqHSaeLvjUVe476ouVwLKn1uVwEFcbJQvnme7W6dTV5SB93x45DEy
You can
check that address here before sending anything.