Understanding line break converters
Three OS conventions, one invisible character.
The thing that ends a line is different on every operating system, and most of the time you don't notice.
LF, CRLF, CR.
Unix and macOS use a single \n (line feed) to end a line. Windows uses \r\n (carriage return + line feed) — a holdover from typewriters and teletype machines, where carriage return moved the carriage left and line feed advanced the paper. Classic Mac OS (System 9 and earlier) used a lone \r, which you almost never see today but might find in a really old file.
When the difference bites.
Most tools are forgiving — modern editors, browsers, and languages handle all three transparently. The places it shows up are: a Git commit on Windows checked out on Mac and the diff explodes; a CSV file from a Windows machine opened in a Unix tool that splits on \n and leaves stray \r at the end of each field; a shell script with CRLF endings that fails because the shebang line ends with \r.
HTML and CSV — special separators.
HTML uses <br> rather than a literal newline; CSV uses commas (with embedded newlines inside quoted fields). The converter understands all of these as either input or output, so you can paste an HTML paragraph with <br> tags and get back a multi-line plain-text version (or vice versa).
The right ending for the destination.
Default to LF for code, configuration files, and anything handed to a Unix tool. Use CRLF for files going to Windows users, especially Notepad (which still struggles with LF alone). Use HTML <br> when the destination is a templated string in a web page. The converter lets you flip between any of these in one pass.