This is how you avoid the date autocorrect
Excel’s import turns values like 1-2 and SEPT9 into dates. Because the cell types are written explicitly here, text stays text. It is the main reason to convert rather than rename.
Convert CSV to Excel
Opening a CSV in Excel and saving it as .xlsx works until Excel decides your product code is a date. This converter builds the workbook directly, writing each value with an explicit cell type, so nothing is reinterpreted on the way in.
- Runs in your browser
- No signup
- No upload
- Free
CSVExcel
Runs on your deviceCSV
Options
Reading CSV
Auto-detect reads the first rows and picks the separator that splits them consistently.
Turn off when the file starts straight into data. Columns are then named column_1, column_2, and so on.
Turns "42" into a number and "true" into a boolean. Values with leading zeros stay text so IDs and zip codes survive.
Which worksheet to convert. Filled in once the workbook is read.
Dotted path to the array of records, such as data.items. Leave empty to use the whole document.
Turns {"user":{"id":7}} into a user.id column. Arrays are kept as JSON text.
Pick the encoding the file was written in. Wrong encoding shows up as garbled accents.
Comma-separated words that should become null instead of text.
Writing Excel
Snappy is the default across Spark, DuckDB and pandas. Gzip is smaller but slower to read.
Turns a user.id column back into {"user":{"id":7}}.
Excel needs a byte order mark to open UTF-8 files with accents correctly.
Rows per row group. Larger groups compress better; smaller groups let readers skip more.
Converting…
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Work with Parquet as well?See ParquetReader with ParquetReader — opens Parquet files directly.What happens
How this converter handles CSV to Excel
- Parses the CSV, detecting the delimiter and honouring quoted fields.
- Infers a type per value and writes it as a typed Excel cell: numbers as numbers, booleans as booleans, text as text.
- Writes the header row in bold and freezes it, so it stays visible while scrolling.
- Produces a genuine .xlsx workbook, not a renamed CSV.
Format differences
CSV vs Excel
Plain text rows that open anywhere, with no types and no schema. Spreadsheet workbooks with sheets, formatting and cell types.
| CSV | Excel | |
|---|---|---|
| Type information | None — every value is text | Per cell — text, number, date, boolean |
| Structure | Flat rows and columns | Sheets of rows and columns |
| Compression | None | Zipped XML |
| Typical file size | Baseline (100%) | Smaller than CSV, larger than Parquet |
| Schema | Header row at best | None beyond the header row |
| Human-readable | Yes, in any text editor | Only in a spreadsheet app |
| Tool support | Universal | Excel, Google Sheets, LibreOffice |
Worth knowing
What to watch out for
Excel has hard limits
A worksheet holds 1,048,576 rows and 16,384 columns. Larger inputs are truncated and the conversion tells you so. For bigger data, Parquet or CSV is the better destination.
Long numbers may still display oddly
Excel shows numbers beyond 15 significant digits in scientific notation and rounds them internally. Long identifiers are safest kept as text — leading zeros already are.
When you need this
Common reasons to convert CSV to Excel
Sharing a report with non-technical colleagues
A formatted workbook with a frozen header reads as a finished deliverable; a raw CSV reads as homework.
Avoiding the import dialog entirely
No delimiter prompts, no encoding guesses, no accidental type conversions.
Preparing a template for manual editing
Correct types up front means fewer broken cells after someone edits the file.
FAQ
CSV to Excel questions
Is my CSV uploaded?
No. The conversion runs in your browser using WebAssembly and JavaScript. The file is read from your disk into a Web Worker, converted in memory, and handed back as a download. It is never sent to a server, so there is nothing for us to store, log or leak.
Why not just rename the file to .xlsx?
Because .xlsx is a zipped XML package, not delimited text. Renaming produces a file Excel refuses to open. This converter builds the actual workbook structure.
Will Excel turn my codes into dates?
No. Each cell is written with an explicit type, so values that would normally trigger Excel’s autocorrect are stored as text and stay as typed.
Can I set the sheet name?
Yes, in the output options. Excel limits sheet names to 31 characters, so longer names are trimmed.
What if my CSV has more than a million rows?
It will be truncated to Excel’s limit and you will get a warning. Convert to Parquet instead if you need the whole dataset.
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