Paste CSV and see it as a spreadsheet straight away - numbers, dates and IDs kept the way Excel should hold them. Download the .xlsx only if you want it.
The spreadsheet appears here as you paste.
A report export, a bank statement, a data dump from a colleague - CSV is how tables travel, but opening one in Excel often mangles it: PIN codes lose their leading zero, account numbers turn into 1.23E+15, and dates flip between formats. Paste the CSV here and see exactly how it will look as a spreadsheet before you decide to download it.
Excel stores numbers with 15 significant digits, so a 16-digit card or account number silently changes. A value with a leading zero, like a PIN code or employee ID, loses it. This tool only converts a value to a number or date when nothing is lost, and keeps everything else as the exact text you pasted.
A CSV cell beginning with = can be a formula that runs when the file is opened, a known way to attack whoever opens an exported sheet. Every text cell in the workbook is written as plain text, so nothing in the CSV can execute.
With "Detect numbers and dates" on, each cell is checked on its own. 125000.50 becomes the number 125000.5 (format the column in Excel to show two decimals) and -1500.75 stays negative. 007 and the PIN code 040001 keep their leading zero as text. 123456789012345 (15 digits) is a number, but 1234567890123456 (16 digits) stays text, so no digit is rounded away. 2026-10-01 and 31/10/2026 become real dates; 2026-02-30 is not a real day and stays text. Thousands separators and decimal commas (1,234 or 1.234,56), percent signs (12%), exponents (1e5) and a leading + all stay text, exactly as pasted. Header cells are always text.
A value wrapped in double quotes is one cell, whatever it holds: "Rao & Sons, Pune" keeps its comma, a quoted address with a line break stays in one cell, and two double quotes inside quotes are one, so "Quote ""Q4"" retainer" becomes Quote "Q4" retainer. The delimiter is detected from the first 20 lines: of comma, semicolon, tab and pipe, the one that appears most often on the first line and the same number of times on the lines after it wins, so a semicolon file from an Excel set up for decimal commas is read correctly. If the columns in the preview look wrong, pick the delimiter yourself. Blank lines in the middle stay as empty rows; blank lines at the end are dropped. Spaces around a number are ignored when it is typed (" 42 " becomes 42), but a text cell keeps its spaces exactly.
Open file reads the file as UTF-8, which is what Excel's CSV UTF-8 option, Google Sheets and most systems write. A file saved as plain CSV in Excel for Windows usually uses an older Windows code page instead, and then letters such as é, ü or ñ show as �. Save it again as CSV UTF-8, or open it in a text editor that shows it correctly and paste the text here. A byte order mark at the start of the file is removed, so it never sticks to the first header. The other way round, the downloaded .xlsx stores text as Unicode, so names in Hindi, Arabic or Chinese that look right in the preview also look right in Excel, which a UTF-8 CSV without a byte order mark often does not when double-clicked in Excel for Windows.
The preview is built in your browser. Only when you press Download is the CSV sent to the server, which builds the workbook in memory and returns it in the same response. Nothing is written to disk, and the usage record holds only the row and column counts, the delimiter and the header setting, never cell values or the file name.
yyyy-mm-dd and dd/mm/yyyy. They become real Excel dates shown as dd/mm/yyyy. Anything else stays text, so nothing is guessed.
Up to 5,000,000 characters, 100,000 rows and 500 columns. The preview shows the first 500 rows; the download has all of them. A cell longer than 32,767 characters, Excel's own limit, is cut to that length. Downloads are limited to 40 per 10 minutes per IP address.
Slash dates are read as day/month/year only. 10/31/2026 cannot be a day-first date, so it stays text, but 03/04/2026 becomes 3 April 2026, not 4 March. If your file uses month-first dates, untick "Detect numbers and dates" to keep every cell as the exact text, or export the dates as yyyy-mm-dd, which is never ambiguous.
One sheet, named after the file name you type (cut to 31 characters, Excel's limit for sheet names), or data if you leave it empty. With "First row is a header" on, that row is bold on a light grey fill, frozen so it stays in view as you scroll, and has filter buttons on every column. Each column is as wide as its longest value, up to 60 characters. Dates use the dd/mm/yyyy format, empty fields stay empty cells, and the file holds no formulas or macros. Cells you edit in the preview are part of the download.
Only for codes of one fixed length. When Excel turns a value into a number it drops leading zeros and keeps 15 significant digits, so a 16-digit account number such as 1234567890123456 has already lost its last digit: reopen the original CSV instead of repairing the sheet. For six-digit PIN codes, =TEXT(A1,"000000") in a new column gives back 040001 as text, and the custom number format 000000 shows the zeros while the cell stays a number. To avoid it, convert the CSV here: 040001 and 1234567890123456 are written as text cells. In Excel itself, import with Data > From Text/CSV and set those columns to Text before loading, or in Microsoft 365 turn off the leading-zero and 15-digit options under File > Options > Data > Automatic Data Conversion.
Only plain numbers are converted: an optional minus sign, digits, and at most one full stop as the decimal point, such as 1234.50 or -42. Thousands separators (1,234.50), a decimal comma (12,5), currency signs ($100), percent signs (50%), a leading plus (+5), exponents (1e5) and whole numbers with a leading zero (007) stay as the exact text, because reading them would mean guessing the format. To turn such a column into numbers in Excel, =NUMBERVALUE(A2,".",",") reads 1,234.50 as 1234.5 and =NUMBERVALUE(A2,",",".") reads 2.500,27 as 2500.27; the function name and the argument separator (, or ;) follow your Excel language and region. A converted 1234.50 shows as 1234.5 until you give the column a two-decimal number format.
No, it is deliberate. Values such as 040001 or the 16-digit 1234567890123456 are written as text cells so their zeros and digits survive, and Excel's error checking flags any text that looks like a number. SUM and AVERAGE skip text cells in a range, which is right for IDs and codes, but it means a text column is not an amount you can total. To hide the flag, select the cells, click the warning icon and choose Ignore Error, or clear Numbers formatted as text or preceded by an apostrophe under File > Options > Formulas > Error checking rules. Choose Convert to Number only for columns where leading zeros and digits beyond the 15th do not matter.