Text File Generator
Numbering lines by hand is fine for ten of them and miserable for two hundred, and it falls apart entirely the moment you insert a line in the middle. Paste your text here and the numbers are written in for you, formatted the way you want them.
Starting somewhere other than one
The starting number and the step are separate settings, which covers more situations than it first appears. Numbering an excerpt that begins partway through a file? Start at 47 so the numbers match the source. Continuing a list from another document that ended at 120? Start at 121. Labelling something that counts in tens, or numbering only every other item? Set the step accordingly.
Negative starting values are allowed too, which occasionally matters for offsets and countdowns where the first few rows sit before a zero point.
Why the numbers look ragged, and how to fix it
Once a list crosses from single to double digits, the text after each number stops lining up. Line 9 and line 10 start their content one character apart, and on a long list that ragged edge is visibly untidy.
Two options solve it in different ways. Zero padding writes 001, 002, and so on, using as many digits as the highest number needs, which is common in file naming and sorted references because it also makes the list sort correctly as text. Right alignment pads with spaces instead, giving you the same clean edge without changing the numbers themselves. Both only look right in a monospaced font, so if you are pasting into a document set in a proportional typeface, alignment will drift regardless.
Blank lines and what to do with them
By default every line gets a number, empty ones included, which is what you want when the numbers have to correspond to real positions in a file. Somebody reporting an error on line 34 means the thirty fourth line, blank ones counted.
For a written list, numbering the gaps between paragraphs is just noise. Turn on the skip option and blank lines pass through untouched while the numbering continues across them, so the visible items get 1, 2, 3 in sequence with the spacing intact between them.
Getting numbered text into a spreadsheet
Pick the tab separator and each numbered line arrives in a spreadsheet as two columns, the number in one and the text in the other. That is far more useful than a single column with the numbers glued to the front, since you can then sort, filter, or reference either part on its own.
For anything else, the custom separator box takes whatever characters you want between the number and the line, so a pipe, an arrow, or a bracket style your own system uses is one entry away.