Question 1

What does this tool do?

Accepted Answer

It converts CSV (comma-separated values) files into XLSX (Microsoft Excel Open XML) spreadsheets. Each CSV becomes one sheet in the workbook. Cells are auto-typed as numbers, dates, booleans, or text. The output opens in Excel, LibreOffice, Google Sheets, and Numbers.

Question 2

Does it use SheetJS or any external library?

Accepted Answer

No. We wrote a minimal pure-JS XLSX writer that emits the Office Open XML format directly — XML files for sheets, shared strings, and workbook structure, packaged in a ZIP (STORE method, no compression). The entire writer is ~300 lines and ships in the tool's bundle, no third-party dependency.

Question 3

How are cell types detected?

Accepted Answer

For each cell value we try: (1) boolean (true/false/yes/no), (2) integer / decimal / scientific notation, (3) ISO date (YYYY-MM-DD), (4) date with slashes, (5) time, (6) anything else becomes text. The first match wins. You can also force all cells to text with a toggle.

Question 4

What's the maximum CSV size?

Accepted Answer

There's no hard limit, but very large CSVs (1M+ rows) will use lots of memory since we parse the whole file. For most use cases (under 100K rows) conversion takes under a second. We use shared strings deduplication to keep XLSX size reasonable for text-heavy data.

Question 5

Can I convert multiple CSVs at once?

Accepted Answer

Yes. Drag-drop multiple CSV files and they become multiple sheets in one workbook. Each CSV's filename (without extension) becomes the sheet name. You can also rename sheets before conversion.

Question 6

What extra features does this tool have compared to others?

Accepted Answer

10 extras: (1) Drag-drop multiple CSVs. (2) Batch convert — multiple CSVs into one multi-sheet XLSX. (3) Custom sheet names per CSV. (4) Header row styling (bold + light fill). (5) Auto-fit column widths based on content. (6) Stats panel — rows, columns, file size, sheet count. (7) Preview first 10 rows of each CSV before converting. (8) Custom delimiter (comma, tab, semicolon, pipe, auto-detect). (9) Encoding detection (UTF-8 BOM handling). (10) History of recent conversions (localStorage).

Question 7

Is my CSV uploaded anywhere?

Accepted Answer

No. All parsing and XLSX generation runs in your browser. The CSV contents never leave your device. Only conversion summaries (filename, row count) are saved to local history — never the actual data.

Question 8

Why is the output XLSX larger than my CSV?

Accepted Answer

XLSX is a ZIP containing XML — for small datasets the XML overhead exceeds the compression savings. For large text-heavy datasets, our shared-strings deduplication usually makes XLSX smaller than CSV. For pure-number data, CSV is almost always smaller.

CSV to Excel Converter

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