How to use
1. Upload your CSV files
Drag & drop one or more .csv files onto the upload zone, or click to browse. Multiple files are supported — you can convert them all at once.
2. Configure conversion settings
Choose the delimiter (or leave it on Auto-detect), pick the output mode (Separate files or Merge into one), set the date format, and toggle whether the first row contains column headers.
3. Preview & set column types
Review your data in the preview table. For each column you can choose a data type: Auto, Text, Number, Date, or Boolean. Use Text to preserve leading zeros (e.g. postal codes, phone numbers, ID numbers).
4. Convert & download
Click Convert to generate the .xlsx file(s). When ready, click Download. If you converted multiple files in Separate mode, you'll get a ZIP archive.
Frequently asked questions
Why are my leading zeros disappearing? (e.g. 00700 becomes 700)+
Excel treats purely numeric values as numbers, dropping leading zeros. Set the column type to Text in the preview step. Text-formatted cells keep leading zeros intact.
My file looks garbled / has weird characters. Why?+
This is usually an encoding mismatch. The app auto-detects UTF-8, UTF-16, and Latin-1/Windows-1252. If text still looks wrong, try re-saving your CSV as UTF-8 in a text editor before uploading.
The data is all in one column instead of separate columns.+
The delimiter was probably misdetected. Open the Conversion Settings section and manually select the correct delimiter (Comma, Semicolon, Tab, or Pipe) instead of Auto-detect.
Dates are showing the wrong day/month.+
This is the dd/mm vs mm/dd ambiguity. In Conversion Settings, choose the Date format that matches your source data (DD/MM/YYYY, MM/DD/YYYY, or YYYY-MM-DD).
Is my data uploaded to a server?+
No. Everything runs 100% in your browser (client-side). Your files never leave your device — this is a core privacy guarantee of the app.
What's the difference between Separate files and Merge into one?+
Separate files produces one .xlsx per CSV (downloaded as a ZIP for multiple files). Merge into one combines all CSVs into a single workbook.
What file size is supported?+
The app handles files up to ~100 MB and around 1 million rows. Very large files may take a few seconds to parse.
Your data stays private
All conversion happens in your browser. No file is ever uploaded to a server.