Open any CSV instantly.

less-sheet is a native, read-only viewer for spreadsheet-sized data, focused on speed and low memory use whatever the file size. Today it reads CSV — plain or gzipped, local or streamed from a URL — with more formats coming.

It never loads the whole file into memory, only the minimum needed to fill the window.

Benchmarks.

Time and memory to get your first look at the data. Both barely move as the file grows.^*

* Very wide CSVs — thousands of columns — do add to the load time.

Memory is quoted as engine + window. Only the first number is about your file, and it is the small one: ten gigabytes, a hundred and thirty-five million rows, rests in under three megabytes. The second is the window itself, and it does not move whatever you open.

Quick toggles for the most common parameters.

Separator, quote character, header row and text encoding are detected from the file itself. You open the file and read it — there is no import step.

When a guess is wrong, each of those is a live control: change it and the open document re-renders in place. No closing, no re-importing, no starting over.

Search & filter.

Quickly find content across the entire file, or filter down to just the rows you need.

Copying returns the original bytes, regardless of any formatting you applied in the viewer.

Where a spreadsheet struggles.

Spreadsheets like Excel and LibreOffice are powerful tools, built to edit and compute. But they load the whole file into memory, interpret its contents, cap how many rows it can have, and make changing the parsing options slow.

less-sheet loads the bare minimum and guesses the parsing options from the data. You can change them easily when it guesses wrong.