Right Click XLSX2CSV2XLSX

Two-way CSV and XLSX conversion from the Windows right-click menu.

One PowerShell file, about 53 KB, and no dependencies: no Excel, no Python, no Node, no PowerShell module. An XLSX file is only a ZIP archive of XML documents, so the script reads and writes the OpenXML package directly.

Menu entries

Install

Download RightClickXlsx2Csv2Xlsx.ps1, put it wherever you want to keep it, and run:

powershell -ExecutionPolicy Bypass -File .\RightClickXlsx2Csv2Xlsx.ps1 -Install

The installer asks which language the menu entries should use. English and French are available, and English is the default. Pass -Language en or -Language fr to skip the prompt, which is what you want for an unattended install.

Everything is written under HKCU, so no administrator rights are needed and no other user account is touched.

To remove everything:

powershell -ExecutionPolicy Bypass -File .\RightClickXlsx2Csv2Xlsx.ps1 -Uninstall

Installing writes one companion file next to the script, RightClickXlsx2Csv2Xlsx.launcher.vbs. It exists only so Explorer does not flash a console window on every conversion, it is about 30 lines, and -Uninstall deletes it. Do not move the folder after installing, because the registry points at both paths. If you do move it, run -Install again.

Macro-enabled workbooks are not registered by default. Add them with -XlsxExtensions .xlsx,.xlsm.

On the command line the converter accepts more than the menu registers: .xlsm reads like .xlsx, and .txt is treated as a CSV. Those two are deliberately left out of the registry, because claiming file types people use for other things is not this tool's business.

Use

Right-click one or more files and pick an entry. On Windows 11 these live under Show more options, the inherited menu, which Shift+F10 opens directly. The short Windows 11 menu only accepts signed MSIX packages, which would mean an installer and a code-signing certificate, the opposite of the goal here.

Output lands next to the source file. An existing file of the same name is never overwritten: a numbered suffix is added instead.

-Delimiter is not sent by the menu when converting a CSV, so the separator of the file being read is always detected. The two CSV entries send it only because there the separator is a choice about the file being written.

Command line

The direction comes from the file extension, so there is nothing to specify:

.\RightClickXlsx2Csv2Xlsx.ps1 sales.csv
.\RightClickXlsx2Csv2Xlsx.ps1 report.xlsx
.\RightClickXlsx2Csv2Xlsx.ps1 *.csv -Force
.\RightClickXlsx2Csv2Xlsx.ps1 report.xlsx -Delimiter "," -Sheet "Q3 results"

One object is emitted per converted file, so the script composes in a pipeline.

A workbook with one sheet produces one CSV. A workbook with several sheets produces one CSV per sheet, each suffixed with the sheet name, so nothing is silently dropped.

What the conversion does

CSV to XLSX

Separator detection counts ;, ,, tab and | outside quotes on the first non-empty line. The Excel sep=; convention on a leading line is honoured and that line is consumed.

Encoding detection looks for a UTF-8, UTF-16 LE or UTF-16 BE byte order mark. Without one, a sample is decoded as strict UTF-8; if that succeeds the file is treated as UTF-8, otherwise as the system ANSI code page.

CSV parsing is delegated to the .NET TextFieldParser, which handles quoted fields, doubled quotes, and separators or line breaks inside a field.

Cell typing turns integers and decimals into numbers. A decimal comma is accepted when the comma is not the field separator. Values with a leading zero such as 0012345 stay text, which preserves reference numbers, postal codes and phone numbers. Past 15 digits a value stays text, because a double no longer holds it exactly.

Dates are recognised in ISO yyyy-MM-dd and yyyy/MM/dd form, plus the short date pattern of the current Windows locale, with or without a time. Dates before 1 March 1900 stay text, since Excel shifts serial numbers before that point.

Formatting gives the header row bold text, a frozen pane, an autofilter, and column widths fitted to the content between 8 and 60 characters.

XLSX to CSV

Shared strings, inline strings, cached formula results, booleans and error values such as #DIV/0! are all resolved to what Excel displays.

Dates are the interesting part. A numeric cell is only a date because its number format says so, so the style table is read and both built-in and custom format codes are classified as date, time or both. Matching serial numbers are rendered with the short date pattern of the current locale. Excel counts a day that never existed, 29 February 1900, and that offset is reproduced, so output matches Excel cell for cell.

Decimal separator follows Excel's own behaviour under auto: a comma when the field separator is a semicolon and the locale uses a decimal comma, a dot otherwise.

Blank rows inside the used range are preserved, so row numbers still line up with the original sheet.

Output is UTF-8 with a byte order mark by default, which is what makes Excel reopen the file with the right encoding.

Technical notes

Both directions stream, in two passes over the input. The first pass measures dimensions, the second writes. Memory use therefore does not depend on file size. Output goes to a temporary file that is renamed at the end, so an interrupted run never leaves a truncated result behind.

Writing uses inlineStr rather than a shared string table. Files are slightly larger, but writing stays streaming and stateless.

Control characters XML forbids are stripped, and <, >, & and quotes are escaped. On the way back, XML entities and Excel's _xHHHH_ escapes are decoded. A line whose quotes are never closed is kept verbatim in a single text cell, so no data is lost.

The reader's inner loop picks cell attributes apart with IndexOf instead of regexes or helper calls. That is what takes a 100,000-row workbook from 195 seconds down to 18.

The launcher hands file paths to PowerShell through environment variables rather than on the command line. WshShell.Run expands %NAME% inside the command string it is given, so a file called Q1 %USERNAME% report.csv would otherwise arrive with the percent section replaced and fail as not found. Environment variables are inherited verbatim, the command string contains no percent sign at all, and no caller-supplied text ever reaches a parser.

Measured on a Windows 11 laptop, 100,000 rows by 8 columns:

A real 1,923-row by 23-column export round-trips through both directions in about a second with all 44,229 cells identical.

Known limits

Writing produces a single sheet, named after the CSV file, with no formulas, conditional formatting or structured tables. Reading covers XLSX only; XLSB and XLS are binary formats and are rejected with a clear message.

A CSV line whose quotes are never closed swallows the following lines, which is inherent to the format.

The short date pattern follows the Windows locale in both directions. A CSV written as MM/dd/yyyy and read on a machine set to dd/MM/yyyy will be misread, so use -AsText or ISO dates in that case.

Changelog

The format follows Keep a Changelog, and this project adheres to Semantic Versioning. -Version prints the version the script reports.

1.0.0 - 2026-09-11

Initial release.

• Two-way conversion between CSV and XLSX, in a single PowerShell file with no external dependencies. The OpenXML package is read and written directly.
• Right-click menu entries: Convert to Excel (.xlsx) on .csv and .tsv, Convert to CSV (;) and Convert to CSV (,) on .xlsx.
• -Install and -Uninstall, writing only under HKCU so no administrator rights are needed. Uninstall removes every verb it finds, whatever extensions were registered.
• Menu and message language selectable at install time, English or French.
• Separator detection over a whole logical CSV record, covering ;, ,, tab and |, plus the Excel sep= convention.
• Encoding detection by byte order mark, falling back to a strict UTF-8 test and then to the system ANSI code page.
• Number and date typing on the way in, with leading zeros, long digit strings and pre-1900 dates kept as text.
• Date, time and elapsed-time number formats resolved on the way out, including Excel's 29 February 1900 offset and the 1904 calendar.
• Shared strings, inline strings, cached formula results, booleans and error values resolved to what Excel displays.
• One CSV per sheet for multi-sheet workbooks, so nothing is dropped silently.
• Streaming in both directions, in two passes, so memory use does not track file size. Output is written to a temporary file and renamed.

Requirements

Windows with PowerShell 5.1, which ships with Windows 10 and 11. Nothing else.

Licence

GNU Affero General Public License, version 3 or later. The full text is in LICENSE.

In short: you may use, study, modify and redistribute this tool freely, and any modified version you distribute, or make available to users over a network, must be offered under the same licence with its source. It comes with absolutely no warranty.

SPDX-License-Identifier: AGPL-3.0-or-later