Convert · .csv → .xlsx
Convert CSV to XLSX in Your Browser
Turn a plain .csv file into a formatted Excel .xlsx — without uploading it anywhere. The whole conversion happens locally in your browser.
How it works
- Click Open your CSV to launch the editor in your browser.
- Pick the .csv file from your device, or drag and drop it onto the page.
- Format the cells if you like, then choose Download as / Save as and pick XLSX.
- The XLSX is generated on your device and downloaded — nothing is uploaded.
The CSV is parsed into a real spreadsheet by the OnlyOffice engine, so your rows and columns stay intact and you can add formatting or formulas before saving as XLSX. No Excel, no account, works offline.
The conversion is handled by OnlyOffice's x2t engine compiled to WebAssembly, which targets the common office and text formats — Word, Excel and PowerPoint plus PDF, TXT, HTML and CSV. Because it runs in the browser tab there is no upload queue and no server-imposed size cap, and your data never touches the network. The delimiter (comma, semicolon or tab) and the text encoding are detected automatically — strict UTF-8 first, then GB18030 (the "ANSI" encoding Excel uses for Chinese exports), then Latin-1 — so files that show mojibake elsewhere open with the right characters here. Mark number, date or text columns in the sheet, then save the result as XLSX.
Going the other way is just as common: a system hands you a raw CSV export and you want a tidy, formatted workbook to read or share. Opening it here turns the flat file into a real spreadsheet, where you can widen columns, add headers, apply number and date formats and even write formulas before saving as XLSX — all without uploading the data anywhere. It is a quick way to make a machine-generated export presentable.
Frequently asked questions
How do I convert CSV to XLSX here?
Open the CSV in the editor, then use Download as / Save as XLSX — the conversion runs in your browser.
Is my file uploaded to convert it?
No. It runs entirely in your browser, so your data is never uploaded.
Will my columns and rows stay intact?
Yes. The CSV is parsed into a real spreadsheet, so rows and columns are preserved.
Do I need Excel or an account?
No Excel, no subscription and no sign up.
Will number and date columns be detected?
The CSV becomes a real spreadsheet, so you can set number, date and text cell formats before saving as XLSX.
What delimiter and encoding does it expect?
Comma, semicolon or tab are detected automatically, and so is the encoding: UTF-8 (with or without BOM), GB18030 / GBK for Chinese "ANSI" exports, and Latin-1 as the last resort.
My CSV shows garbled characters (mojibake) in other tools — will it here?
Usually not. Mojibake means the file was saved in a legacy code page (GBK / GB18030 for Chinese, Latin-1 for Western European) and opened as UTF-8. This converter sniffs the bytes first, so Chinese exports from Excel open correctly, and saving writes UTF-8 with a byte-order mark that Excel reads without a wizard.
Does the converter work offline?
Yes. Once loaded it is an installable PWA, so it keeps working with no internet connection.