CSV to Excel (XLSX) Converter

What this tool does

• Writes a genuine .xlsx — a real workbook Excel, Numbers and Google Sheets all open.
• Protects your data's shape — leading zeros, long account numbers and text never get "helpfully" converted.
• Handles real CSV — quoted fields, embedded commas and newlines, CRLF or LF, and a UTF-8 BOM.
• Keeps it local — the workbook is built in your browser; nothing is uploaded.

How numbers are handled

This is where most CSV → Excel converters quietly damage your data. A spreadsheet has no idea that 00704 is a ZIP code; treat it as a number and Excel shows 704. So the rule here is strict: a value becomes a number only when it would read back exactly as typed.

• 42, 0, -5, 0.5 → written as numbers, so you can sum and sort them.
• 00704, 00210 → written as text, so the leading zero survives.
• 3.10, 1,234, 1e5, .5 → text, exactly as typed.
• 9007199254740993 → text, because a spreadsheet would round it.

The summary under the tool tells you how many cells went each way, so you can see the rule at work before you download. If you'd rather nothing were converted at all, switch Numbers to Everything as text.

Why build the workbook in the browser?

A CSV you need in Excel often holds payroll, invoices, customer lists or health records — the files you'd least want sitting on someone else's server. This tool has no upload step and no backend to receive one: the workbook is assembled locally and handed straight to your downloads folder. The trade-off is that the file is stored uncompressed, so it's somewhat larger than one a desktop application would write.