Convert Excel (.xlsx, .xls) spreadsheets to clean CSV files
Convert Excel workbooks (.xlsx, .xls) into clean, standard CSV files with date repair and multi-sheet selection.
🛡️ Your rows never leave your browser.
Why Onfyt: Processes excel to csv entirely in-browser with dedicated Web Workers so your rows never leave your machine.
Interactive Sample Data
| invoice_no | client_name | issue_date | total_amount | status |
|---|---|---|---|---|
| INV-2026-01 | Safaricom Ltd | 2026-01-10 | 450000.00 | Paid |
| INV-2026-02 | Equity Bank | 2026-01-15 | 125000.00 | Paid |
| INV-2026-03 | KCB Group | 2026-02-01 | 89000.00 | Pending |
| INV-2026-04 | Bamburi Cement | 2026-02-20 | 310000.00 | Pending |
How this tool works
Microsoft Excel (.xlsx and .xls) workbooks are the standard data format in business and corporate finance. However, importing Excel files into databases, cloud data warehouses, or analytical scripts often fails due to binary formatting, multi-sheet structures, formula dependencies, and proprietary date serial storage.
When Excel exports to CSV natively, several issues frequently arise. Dates formatted nicely on screen often export as raw numeric serial integers (e.g. 45312) rather than recognizable dates. Formula cells can export with errors or calculation tags rather than evaluated values, and blank cells at the edges of the spreadsheet generate ghost empty columns. Furthermore, multi-sheet workbooks can only be exported one sheet at a time through manual dialogs, slowing down batch migration workflows.
DataFix converts Excel files to clean CSV using client-side SheetJS engines. It evaluates formulas to export computed values, standardizes date serial numbers into clean ISO 8601 strings (YYYY-MM-DD), and allows you to select which worksheet to export. The converter also detects and unmerges merged cells, filling down the parent value across span ranges to prevent data holes.
Your financial ledgers, salary spreadsheets, and client lists never leave your computer. The entire conversion happens in your local browser sandbox with zero network transmission, providing enterprise-grade security and instant performance.
From a technical parsing standpoint, extracting clean CSV data from binary Microsoft Excel workbooks (.xlsx and .xls) requires specialized OpenXML decompression and formula evaluation. Excel stores dates as numeric serial offsets counting from December 30, 1899, leading naive CSV exporters to output cryptic integers (e.g., 45312) instead of recognizable calendar dates. DataFix incorporates client-side SheetJS engines that evaluate cached formula results, convert date serials into standard ISO 8601 strings, and unmerge merged cells while filling down parent values across cell ranges.
From a corporate finance and compliance standpoint, local browser-based spreadsheet conversion is essential. Financial spreadsheets, salary ledgers, and executive compensation matrices contain highly sensitive corporate information that cannot be uploaded to unverified third-party cloud conversion tools under corporate governance policies and data privacy regulations. With DataFix, all Excel workbook parsing executes locally in-browser via Web Workers, ensuring complete data sovereignty, zero network latency, and continuous offline availability.
Things that usually go wrong
- Excel Date Serials (45312): Excel stores dates as numbers counting from 1900. DataFix automatically detects date formats and converts them to standard YYYY-MM-DD.
- Uncalculated Formulas: Files saved without recalculation may display formula text. DataFix extracts the cached evaluated value.
- Merged Cells: Merged cells can cause data gaps in CSV. DataFix provides an option to unmerge and fill down values.
Edge cases we tested
🧪 Empty cells or missing values
Safely handled without schema corruption.
🧪 Leading or trailing cell whitespace
Sanitized prior to processing.
🧪 Large files with 25,000+ rows
Streamed via client-side Web Worker without tab freezing.
Frequently Asked Questions
Does it support both .xlsx and old .xls files?
Yes. Both modern XML-based .xlsx and legacy binary .xls formats are fully supported.
Can I convert multi-sheet workbooks?
Yes. You can preview and convert any sheet within your multi-sheet workbook.
What happens to Excel formulas?
The evaluated calculation results are extracted into the CSV output.
Is my spreadsheet uploaded anywhere?
No. The entire conversion runs locally inside your browser using client-side Web Workers.
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