When line numbers help
Numbered lines make it much easier to reference a specific row when reviewing code snippets, scripts, poetry drafts, or line-separated data with someone else - "check line 14" is a lot clearer than describing where a line sits. This tool just prepends a number and a period to each line; it doesn't touch the actual content, so pasting the result elsewhere keeps your original text intact alongside the numbering.
Why skipping blank lines is a separate option
Some use cases want every line numbered, including blanks, to preserve an exact row-by-row reference (useful when comparing against a tool that also counts blank lines, like most code editors). Others want blank lines left alone so the numbering only tracks actual content lines - which reads more naturally for things like numbered lists of items separated by blank spacing. Having both available covers either case without extra manual cleanup.
Why you can change the separator and starting number
A plain "number, period, space" prefix suits plain text and chat messages, but it isn't the only format people need - "1)" reads more like a numbered outline, "1:" suits some log formats, and a tab character lines numbers up into clean columns when pasted into a spreadsheet or fixed-width editor. The starting number matters when you're numbering a snippet that continues from an earlier block (for example, lines 51 onward of a longer file) and want the numbers to reflect that, rather than restarting from 1.
A note on line-ending differences
The tool recognizes all three common line-ending styles (Windows-style, old Mac-style, and Unix-style) when splitting your pasted text into lines - so content copied from different operating systems or editors numbers correctly either way, rather than being miscounted as one giant unbroken line.