Is my spreadsheet uploaded to a server?

No. The file is read and parsed with ExcelJS entirely in your browser tab. Nothing is transmitted or stored.

How are multiple sheets handled?

All sheet names are listed in a dropdown. Pick one, click Convert, then download or copy that sheet's CSV. Switch to another sheet and repeat to export each one.

Why are my formulas showing as static values?

CSV is a plain-text format with no formula support. ExcelJS reads the last cached value stored for each cell. If a formula has no cached result, the cell may be empty.

Which delimiter should I pick?

Comma is the most widely supported. Use semicolon if your data contains commas (common in European locales where the comma is the decimal separator). Tab is good for piping into terminal tools; pipe is useful for logs.

Developer Tools

Excel to CSV

Convert Excel spreadsheets (.xlsx and .xlsm) into CSV directly in your browser. Drag a file in, pick the sheet you want (workbooks with multiple sheets are fully supported), choose a delimiter and download the CSV — or copy it to your clipboard. A live preview shows the parsed data. Your file never leaves your device.

Your input is processed locally in your browser. It is not uploaded to Dueneo.

Loading Excel to CSV…

How to use

1
Upload your spreadsheet
Drag an .xlsx or .xlsm file onto the dropzone, or click to browse. The file is parsed entirely in your browser — it is never uploaded.
2
Pick a sheet
If the workbook has multiple sheets, use the dropdown to switch between them. Each sheet is converted separately so you can download each as its own CSV.
3
Choose a delimiter
Comma (default), semicolon, tab or pipe. Pick a character that does not appear inside your cell values to avoid quoting issues in downstream tools.
4
Convert, copy or download
Click Convert sheet, then use Copy to put the CSV on your clipboard or Download .csv to save it. The preview shows the first 200 rows of the parsed data.

Common use cases

Export a single sheet from a multi-sheet workbook to a flat CSV for ingestion by another tool.
Convert an .xlsx or .xlsm file to CSV without installing desktop software.
Quickly inspect the contents of a spreadsheet without opening Excel.
Produce tab- or pipe-delimited files for pipelines that do not handle quoted CSV well.

Limitations

Files are capped at 25 MB to keep the browser tab responsive. For very large workbooks, split the file or export sheets individually from Excel first.
Formulas are resolved to their cached values. If a formula has never been opened in Excel (so no cached value exists), the cell will be empty in the CSV.
Cell formatting, colours, merged cells, charts, images and pivot tables are not preserved — CSV has no concept of these.
Multi-line cell contents are quoted per RFC-4180 when needed. Some older tools may not handle embedded newlines correctly.
The sheet name is appended to the downloaded filename. Long or Unicode names are truncated and stripped of unsafe characters.

Frequently asked questions

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JSON Formatter

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Loading Excel to CSV…

Excel to CSV

How to use

Upload your spreadsheet

Drag an .xlsx or .xlsm file onto the dropzone, or click to browse. The file is parsed entirely in your browser — it is never uploaded.

Pick a sheet

If the workbook has multiple sheets, use the dropdown to switch between them. Each sheet is converted separately so you can download each as its own CSV.

Choose a delimiter

Comma (default), semicolon, tab or pipe. Pick a character that does not appear inside your cell values to avoid quoting issues in downstream tools.

Convert, copy or download

Click Convert sheet, then use Copy to put the CSV on your clipboard or Download .csv to save it. The preview shows the first 200 rows of the parsed data.

Common use cases

Export a single sheet from a multi-sheet workbook to a flat CSV for ingestion by another tool.

Convert an .xlsx or .xlsm file to CSV without installing desktop software.

Quickly inspect the contents of a spreadsheet without opening Excel.

Produce tab- or pipe-delimited files for pipelines that do not handle quoted CSV well.

Limitations

Files are capped at 25 MB to keep the browser tab responsive. For very large workbooks, split the file or export sheets individually from Excel first.
Formulas are resolved to their cached values. If a formula has never been opened in Excel (so no cached value exists), the cell will be empty in the CSV.
Cell formatting, colours, merged cells, charts, images and pivot tables are not preserved — CSV has no concept of these.
Multi-line cell contents are quoted per RFC-4180 when needed. Some older tools may not handle embedded newlines correctly.
The sheet name is appended to the downloaded filename. Long or Unicode names are truncated and stripped of unsafe characters.