Pick the columns you keep by name or number and reorder them. Quoted commas and line breaks survive.
Separate entries with spaces or commas. Numbers are 1-based. "2-4" takes columns two through four, and "4-2" takes the same columns in reverse order. Header names are matched exactly, so stray spaces will not match.
A leading hyphen excludes. Writing only "-notes" outputs every column except notes, in the original order. Mixing them, as in "1-5 -3", gives four columns: one to five without the third.
Ticking "Treat the first row as a header" lets you use the first row's text as column names. The first row is still included in the output; the headers of the selected columns stay on top.
The widest row sets the column count. Rows with missing cells are padded with empty strings so that every output row has the same number of columns.
Both work. When "Treat the first row as a header" is ticked you can type the header text directly. Numbers are 1-based counting from the left. Names and numbers can be mixed in the same specification.
Yes. Columns come out in the order you write them, so "3,1,2" outputs the third, first and second column in that order. Writing the same column twice outputs it twice.
Yes. Prefix a column with a hyphen to exclude it. If your specification contains only hyphenated entries, it means "output every other column in the original order". Mixed with normal entries, the hyphenated ones are removed from what you selected.
They survive. The input is read with the CSV quoting rules, and on output only the cells that need it are re-quoted, with inner double quotes doubled.
No. Everything runs inside your browser in JavaScript, and nothing you paste is sent to a server.