What Is a CSV File and How Do You Open It?

By the Opener team·Updated November 11, 2026·5 min read

A CSV file is a plain-text table: each line is one row, and the values in a row are separated by commas (sometimes semicolons or tabs). CSV stands for “comma-separated values”, and banks, shops and web services use it because almost any program can read it. To see it as a proper table, open it in a CSV viewer such as Opener’s CSV viewer, or in Excel, Google Sheets or Numbers.

What’s inside a CSV file

Say your bank let you download your transactions as report.csv. If you open it in a text editor, you’ll see something like this:

Date,Description,Amount,Balance
2026-10-01,Coffee shop,-3.50,1246.50
2026-10-02,"Rent, October",-850.00,396.50
2026-10-05,Salary,2100.00,2496.50

That’s the whole file format:

• One row per line. The first line is usually a header with column names.
• A separator between values. Here it’s a comma. Many European services use a semicolon instead, because the comma is their decimal mark; tab-separated files are often called TSV.
• Quotes around tricky values. "Rent, October" contains a comma, so it’s wrapped in quotes to show the comma is part of the text, not a new column.
• Nothing else. No fonts, colours, formulas, column widths or multiple sheets — just text.

Because it’s plain text, the file also has a text encoding — the way letters are stored as bytes. Modern files use UTF-8, which handles every language. Older systems sometimes use legacy encodings, which is where garbled accents and symbols come from.

CSV vs Excel (.xlsx)

People often treat CSV as “an Excel file”, because Excel opens it. They’re quite different:

Services export CSV because it’s the lowest common denominator: your bank doesn’t know whether you use Excel, Google Sheets, accounting software or a script, and CSV works with all of them. If you receive an .xlsx instead, the Excel viewer or any spreadsheet app opens it.

How to open a CSV file

Opener (any browser, no install). Drop the file into the CSV viewer. It detects the separator (comma, semicolon, tab or pipe) and the encoding automatically and shows a clean table. You can search across all columns and sort by any column. The file is read in your browser and not uploaded — a sensible default for bank statements. It doesn’t edit the file.

Excel. Double-clicking a CSV usually opens it in Excel if Excel is installed. It’s convenient, but Excel guesses what each value means: it can drop leading zeros from account numbers or postcodes, show long numbers in scientific notation, and reinterpret some text as dates. Excel’s data import feature lets you set column types first and avoids most of this.

Google Sheets. Create a blank spreadsheet and use the import option in the File menu, or upload the CSV to Google Drive and open it with Google Sheets. You can choose the separator during import.

Numbers (Mac). Numbers opens CSV files directly; double-click or open it from the app.

A text editor. Notepad on Windows or TextEdit on Mac shows the raw text. It’s not comfortable for reading, but it’s the quickest way to check what separator the file uses or whether the text is garbled.

Common problems (and fixes)

CSV’s simplicity has a downside: there’s no rule saying which separator or encoding to use, so files from different systems don’t always open cleanly.

• Strange characters instead of letters (é, ’ or question marks): the app read the file with the wrong encoding. See why a CSV shows strange characters.
• Everything in one column: the file uses a different separator from the one your spreadsheet expects, typically semicolons versus commas. See what to do when a CSV opens in one column.
• The file is too big: Excel stops at 1,048,576 rows, and large exports from web services can exceed that. See how to open a CSV that’s too big for Excel.
• Numbers or dates changed: leading zeros vanished or dates swapped day and month. That’s the spreadsheet reformatting values, not the file being wrong — import with column types set to text, or view it in a CSV viewer that leaves values as they are.

Opener’s CSV viewer handles the first three automatically: it detects UTF-8, Windows-1251 and Windows-1252 encodings, picks up the separator, and opens files with millions of rows on a normal laptop.

How to save or export as CSV

Sometimes you need to go the other way — upload a list to a service that only accepts CSV.

• Excel: use Save As and pick a CSV type. If you see a “CSV UTF-8” option, choose it so accented letters and symbols survive.
• Google Sheets: download the sheet as comma-separated values from the File menu.
• Numbers: export the spreadsheet to CSV from the File menu.
• LibreOffice Calc: use Save As, choose the text CSV type, and set the separator and encoding in the dialog that follows.
• Opener: after searching and sorting in the CSV viewer, export the result as clean UTF-8 CSV, or as JSON for developers. The Excel viewer can export any sheet of an .xlsx as CSV the same way.

Two things to know before you export: only the current sheet is saved, because CSV holds a single table; and formulas are replaced by their values while all formatting is lost. Keep your original .xlsx if you need those.

Frequently asked questions

Is a CSV file safe to open?

A CSV is plain text and can’t run programs by itself. Spreadsheet apps can interpret cells that start with = as formulas, so be careful with CSV files from unknown senders. A CSV viewer or text editor only shows the text.

Can I open a CSV file on my phone?

Yes. The CSV viewer runs in any mobile browser, and the Google Sheets, Numbers and Excel apps can open CSV files too.

Why does my CSV use semicolons instead of commas?

Systems set up for countries that use a comma as the decimal mark often separate values with semicolons so that numbers like 3,50 stay intact. Most apps can handle it if you choose the separator on import.

What’s the difference between CSV and TSV?

Only the separator: TSV uses tabs instead of commas. Most spreadsheet apps and CSV viewers open both.