Combine CSV files
Choose one or more CSV files. Each file becomes one worksheet in a single XLSX workbook.
Turn a group of CSV files into one workbook
This converter puts each selected CSV file on its own worksheet and writes the worksheets to a single combined.xlsx file. The source filename becomes the worksheet name. Characters Excel does not allow are replaced, names are limited to 31 characters, and repeated names receive a numbered suffix.
CSV delimiters are detected by Papa Parse. Files are read as UTF-8 when the bytes are valid UTF-8, with a Shift_JIS fallback for CSV exports from Japanese spreadsheet software. Cell values are written as text rather than being converted to numbers or dates.
Why your CSV files stay on your device
The conversion has no upload step. The CSV parser and XLSX writer run in the browser:
- Your browser reads the CSV files and creates the workbook.
- The page is served as static files and sends no request containing your CSV data.
- The source code is published under the MIT license.
- After the required files are cached, the tool can run offline.
To verify this, open the browser's Network panel during conversion. No request carries the selected files. Read the source.
How to use it
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Choose the CSV files
Select several .csv files at once, or drop them anywhere on the page. Non-CSV files are left out.
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Let the workbook be created
Each CSV is decoded and parsed, then written to its own worksheet. The progress panel shows which file is being read.
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Download the XLSX
The browser downloads combined.xlsx and lists every worksheet with its source file, row count, and detected encoding.
FAQ
Are my CSV files uploaded?
No. The selected files are read by browser APIs and passed directly to the CSV parser and workbook writer on your device. There is no server-side conversion step.
How are the CSV files arranged in the workbook?
Each CSV file becomes one worksheet, in the same order in which the browser receives the selected files. The output is one XLSX file named combined.xlsx.
What happens to worksheet names that Excel does not accept?
The name starts with the CSV filename without its extension. Backslash, slash, question mark, asterisk, square brackets and colon are replaced with underscores. Names are limited to 31 characters. If two names match, the later one gets a suffix such as “ (2)”.
Does it read Japanese CSV files?
Yes. The converter tries strict UTF-8 first and falls back to Shift_JIS when the bytes are not valid UTF-8. The detected encoding is shown in the result.
Will numbers or dates be reformatted?
No automatic data typing is applied during CSV parsing. Cell values are added to the workbook as text, so the tool does not intentionally turn strings into numbers or dates.
What happens to an empty CSV?
An empty CSV produces an empty worksheet. Blank lines are skipped when the CSV is parsed.
Can I include an XLSX file or edit the data?
No. This tool accepts CSV input and combines files without sorting, aggregating, or removing duplicates. XLSX input belongs in a workbook-merging tool.
Is there a file size limit?
The tool rejects a selection whose combined size exceeds 2 GB. The practical limit may be lower because parsing and workbook creation use the memory available to the browser.
Does it work offline?
Yes. It is a PWA. After the page and its conversion libraries have been cached, it can create workbooks without a network connection.