`.csv` File Extension

Learn what a .csv file contains, which apps open CSV tables, how Poly supports them, and when another data format is a better fit.

File extension details for `.csv`

Full Support

File type	Comma-separated values table
MIME type	`text/csv`
Encoding	Plain text, usually UTF-8; legacy character encodings are possible
Operating systems	Windows, macOS, Linux, ChromeOS, iOS, Android
Opens with	Microsoft Excel, Apple Numbers, LibreOffice Calc, Text editors
Poly support	Yes. Poly provides rich text support for CSV files.
Indexed by Poly	Yes. Poly indexes filenames and readable CSV text for exact and semantic search.
Preview in Poly	Yes. CSV files open in Poly's text editor with syntax highlighting.
Poly agent	Yes. The Poly agent can read and reason about CSV headers, rows, and values.

What kind of file is a `.csv`?

A .csv file stores rows and fields as plain text, usually with commas between fields. It commonly represents one table exported from a spreadsheet, database, analytics tool, or business application. Its registered MIME type is text/csv.¹

CSV is not a complete spreadsheet format. It has no standard way to preserve multiple worksheets, charts, formatting, formulas as calculations, or explicit cell types. Values that look like dates or numbers remain text until an importing application interprets them.

RFC 4180 describes the familiar convention: each record is a line, commas separate fields, and fields containing commas, quotes, or line breaks are enclosed in double quotes. A quote inside a quoted field is doubled.²

CSV has no magic number. A comma is not a reliable signature because ordinary text can contain commas and a valid one-column CSV can contain none. Check the filename, MIME type, character encoding, and parsed row structure together.

How do I open a `.csv` on my computer?

On Windows, open it in Microsoft Excel, LibreOffice Calc, or a text editor.
On macOS, use Apple Numbers, Microsoft Excel, LibreOffice Calc, or a text editor.
On Linux, LibreOffice Calc and many database or programming tools can import it.
On iPhone, iPad, Android, and ChromeOS, spreadsheet apps can open common CSV files.

Import settings matter. A regional spreadsheet configuration may expect semicolons rather than commas, while automatic type detection can strip leading zeros or reinterpret dates. Microsoft recommends importing text when you need control over the delimiter and column interpretation.³

Opening a CSV in Excel does not turn it into an Excel workbook. Save a separate .xlsx copy if you add formatting, formulas, or multiple sheets.

Poly support for `.csv`

Poly previews CSV files in a text editor with syntax highlighting, word wrap, and in-file search. It indexes readable content for exact and semantic search, and the Poly agent can read headers, rows, and values to answer questions about the data.

Poly presents CSV as text rather than a calculated spreadsheet grid. It does not infer durable column types, evaluate spreadsheet formulas, or recreate workbook formatting.

History of `.csv`

Comma-separated data was exchanged between spreadsheet programs long before a shared Internet specification existed. RFC 4180 documented a commonly used form and registered text/csv in October 2005, but it explicitly remained Informational rather than defining a universal standard.²

That history explains why CSV files still vary. Producers may use different delimiters, line endings, encodings, header conventions, and quoting rules. The current IANA registration recommends UTF-8 when no charset parameter is supplied and allows a header parameter with present or absent.¹

Working with `.csv` and alternatives

Choose the format according to what must survive:

Format	Best for	Important limitation
CSV	Broad exchange of one flat table	No workbook features or built-in data types
TSV	Tables whose fields often contain commas	Tabs and line breaks need careful handling
JSON	Nested or typed application data	Less convenient for a simple spreadsheet table
XLSX	Editable spreadsheets	More complex and less suitable for line-oriented tools

Never rename another file to .csv as a conversion. Export it with software that understands the source format, then verify the delimiter, encoding, row widths, headers, and any identifiers that must retain leading zeros.

CSV is passive text, but spreadsheet software may interpret cells beginning with certain characters as formulas. Treat exports containing untrusted input carefully and test safeguards in the applications that will open them.⁴

Internet Assigned Numbers Authority. text/csv Media Type Registration. ↩ ↩²
Shafranovich, Y. RFC 4180: Common Format and MIME Type for Comma-Separated Values (CSV) Files. Internet Engineering Task Force, October 2005. ↩ ↩²
Microsoft Support. Import or Export Text (.txt or .csv) Files. ↩
OWASP Foundation. CSV Injection. ↩

.csv File Extension

File extension details for .csv

What kind of file is a .csv?

How do I open a .csv on my computer?

Poly support for .csv

History of .csv

Working with .csv and alternatives

Footnotes