Convert CSV to XLSX.
CSV turned into a real Excel workbook — on your device.
Drop CSV, Excel, JSON or YAML files here
or browse your files
Paste with ⌘V · or drop files anywhere on the page
Files never leave your device. Everything runs in your browser, nothing touches a server — tools you've used even work offline.
Convert CSV files to real Excel workbooks entirely in your browser — delimiters auto-detected (comma, semicolon, tab), numbers typed as numbers, text kept as text. Drop the .csv, download the .xlsx. Nothing is ever uploaded.
Before / after
CSV — 221 B
Peak,Country,Elevation_m,First_ascent Triglav,Slovenia,2864,1778 Mont Blanc,France,4808,1786 Matterhorn,Switzerland,4478,1865 Grossglockner,Austria,3798,1800 Monte Rosa,Switzerland,4634,1855 Säntis,Switzerland,2502,1846
XLSX — 9 KB
| Peak | Country | Elevation_m | First_ascent |
|---|---|---|---|
| Triglav | Slovenia | 2864 | 1778 |
| Mont Blanc | France | 4808 | 1786 |
| Matterhorn | Switzerland | 4478 | 1865 |
| Grossglockner | Austria | 3798 | 1800 |
| Monte Rosa | Switzerland | 4634 | 1855 |
| Säntis | Switzerland | 2502 | 1846 |
Rows
7
Columns
4
Format
CSV → XLSX
Real result, not a mock-up: the 7-row CSV on the left went through the CSV to XLSX tool — SheetJS, the library behind most of the JavaScript spreadsheet world — and came out as a real .xlsx workbook. The table on the right is read straight back from the downloaded file: numbers became real numeric cells, date-looking strings deliberately stayed text, and none of it ever left the browser.
How it works
- Drop files anywhere on the page, click to browse, or paste with ⌘V.
- Pick a quality or preset — or set an exact target size and let the tool find it.
- Compress, compare before/after, and download — individually or as a ZIP.
What a proper conversion gets right
CSV has no types — everything is text until something interprets it. This tool re-types pure numbers as numeric cells so sums and charts work immediately, while anything ambiguous stays text: date-looking strings, fractions like 1/2 and codes like MARCH1 are NOT silently turned into dates, the classic spreadsheet-import disaster. Quoted fields, embedded commas and multi-line cells all survive; semicolon and tab files (European Excel exports) are detected automatically.
The whole family on one tab
This page is the front door of the data tab: drop any of the four formats and the direction follows the file — XLSX back to CSV, JSON to YAML and YAML to JSON all run through the same engine. Batch a mixed folder and every file comes back converted the right way.
Under the hood
Spreadsheets are read and written by SheetJS — the open-source library behind most of the JavaScript spreadsheet world — and the JSON/YAML side runs on the standard `yaml` parser, both loaded on demand in your browser. Your data never leaves the device: no upload, no server-side copy, and the tools keep working offline once loaded. For business and personal data that is not a nice-to-have — it is the point.
Frequently asked questions
Will my numbers and dates survive?
Numbers become real numeric cells. Date-looking strings deliberately stay text — automatic date guessing is how "1/2" becomes January 2nd in other tools. Format columns as dates in Excel afterwards if you need them typed.
Does it handle semicolon CSVs from European Excel?
Yes — the delimiter is sniffed per file, so comma, semicolon and tab files all convert correctly, decimal commas included.
Is there a size limit?
No hard limit — typical exports convert instantly. Very large files (tens of MB) take a few seconds since everything runs on your own machine.
Is my data uploaded?
No. The conversion runs entirely in your browser — the server only delivers this page. Spreadsheets full of names, prices or personal data never leave your device. Want proof? Run one file through, switch your connection off, and run another — it still works.