Turn CSV or TSV into an .xlsx workbook with bold headers, set column widths and leading zeros kept. Runs on your device.
To convert a CSV file to Excel, paste its text or add the file, check the preview and press Download .xlsx, which gives a standard .xlsx workbook with one sheet per input. The tool reads the text as RFC 4180 CSV: a comma, semicolon, tab or pipe splits the columns, quotes protect a separator inside a value, and a doubled quote inside quotes is one quote. The separator is detected from the first lines unless you pick one. The page opens with a sample of three rows that shows the main rules. In it, 00123 stays the text 00123, 7.5 becomes the number 7.5, 1200.50 becomes the number 1200.5, and the quoted value Said "hello" is written without its outer quotes. The header row is written in bold and frozen, and each column is as wide as its longest value among the first 1000 rows, between 8 and 60 characters.
A cell becomes a number only when it reads back exactly: digits with an optional decimal part or exponent, such as 9, -3, 0.25 or 1e5. Three rules keep data safe. A value with a leading zero, like 00123 or 007, stays text, and so does any number with more than 15 digits, because Excel keeps 15 significant digits and would round the rest, which would damage an ID or a card number. Text kept this way gets the Text format, so it stays text if you edit it in Excel. Everything else that is not a plain number is text: 1,234, 12%, $5 and +91 98765 are not converted. A number with a trailing zero loses it, so 1200.50 is stored as 1200.5; the display format in Excel decides how many decimals show. The header row is always text. Switch off Turn numbers into numbers to keep every cell as text.
Text that starts with = + - or @ is written as text and never as a formula, so a cell such as =1+1 shows exactly that and nothing runs when you open the file. A semicolon-separated file from a European Excel is detected by its semicolons, but a decimal comma such as 3,5 is not converted to a number; it stays text. Files are read as UTF-8 first. A file with a UTF-16 byte-order mark, which Excel's Unicode Text option writes, is converted, and a file that is not valid UTF-8 is read as Windows-1252, with a note on the page. Dates are kept as text: 2026-01-15 is not turned into an Excel date.
Add up to 20 files and each becomes a sheet named after the file, cut to Excel's 31 characters, without the characters Excel forbids, and numbered if two names match. Pasted text becomes the first sheet. One file can be up to 10 MB and all files together up to 30 MB. A sheet holds at most 1,048,576 rows and 16,384 columns, and a cell at most 32,767 characters; anything past those limits is left out and the page tells you how many. The tool does not make charts, formats, formulas or colours, and it does not write the older .xls format. Use Excel to CSV for the other direction.
The text and files are read and the workbook is built by code running in this tab, with no upload and no server that receives your data. Only the three option choices are saved in this browser, never the text or a file name. The page counts visits with Google Analytics, using the tool name and rough size groups such as 1 to 10 MB, never your data.
Add the .csv file or paste its text, look at the preview, and press Download .xlsx. A 4-row sample file comes out as a one-sheet workbook named after the file, such as sales.xlsx, with a bold, frozen header row.
Leave Turn numbers into numbers on. A value such as 00123 or 007 is always kept as text with the Text format, so the zeros stay, and the page counts how many cells it protected. Opening a CSV directly in Excel usually drops them.
Press Add CSV files and choose up to 20 files at once, or add them one after another. Each becomes its own sheet named after the file, so jan.csv and feb.csv give sheets jan and feb. The sheets stay separate; the tool does not stack them into one.
Excel stores 15 significant digits, so a 16-digit value such as 1234567890123456 would be rounded to 1234567890123460 as a number. The tool keeps it as text so the digits are exact. IDs and card numbers are the usual case.
Detect picks the separator that splits most of the first 20 lines the same way, and a file with few lines can fool it. Open Options and choose Semicolon, Comma, Tab or Pipe yourself, and the preview updates at once.
No. The text is processed in your browser and not uploaded. The three option choices are saved in this browser, the data and file names are not. The page counts visits with Google Analytics, using a size group such as 1 to 10 MB.