Line Number Adder: Number Lines of Text Online

Why number lines at all

Line numbers turn vague feedback into precise feedback. Compare the third paragraph reads oddly with line 14 reads oddly. Code reviewers, editors, lawyers, teachers, and transcriptionists all rely on the same trick: a shared reference that survives email, chat, and printouts.

Word processors and code editors show line numbers in the margin, but those numbers disappear the moment you copy the text into Slack, an email, a GitHub comment, or a support ticket. This tool writes the numbers into the text itself, so they travel with it.

How the numbering works

The text is split on line breaks, both Unix (LF) and Windows (CRLF). Each line gets a label made of the current number and your separator, then the counter advances by the step. With start 1, step 1, and a period separator, the first three lines become 1. , 2. , and 3. .

Padding makes every label the same width. The tool works out the largest number you will reach, counts its digits, and pads the others to match. With 120 lines and zero padding, line 7 becomes 007. With space padding it becomes two spaces and a 7, so the text after the numbers lines up in a monospace font.

If you tick Don't number blank lines, empty lines (including lines with only spaces) pass through unchanged and do not consume a number. The width calculation only counts the lines that will actually be numbered.

Worked example

Input, five lines with a blank line in the middle: Preheat the oven to 425°F. / Toss the vegetables with olive oil and salt. / (blank) / Roast for 25 minutes, flipping halfway. / Finish with lemon juice.

Default settings number all five lines 1 to 5, including the blank one, which becomes just 3. followed by nothing. Tick Don't number blank lines and the steps become 1 to 4 with the blank line preserved, which is usually what you want for recipes and instructions. Set start to 10 and step to 10 and you get 10, 20, 30, 40, leaving room to insert a step between any two later.

Choosing a format for the job

Code snippets: use space padding and a pipe or tab separator, like 9 | const x = 1;. It keeps the code aligned and makes it obvious which characters are part of the code. Legal and academic drafts: court filings and many style guides number every line, often in multiples of 1 or 5, so readers can cite a page and line. Transcripts and interviews: numbered lines let researchers quote exact passages, which is standard in qualitative research. Lists and checklists: a period or parenthesis separator reads naturally.

Zero padding helps when the output will be sorted as text. Plain numbers sort as 1, 10, 11, 2; padded numbers sort as 01, 02, 10, 11. That matters if you number file names, rows you will paste into a spreadsheet, or anything a computer will sort alphabetically.

Removing line numbers

The reverse problem is just as common: you copied code from a PDF, a book, or a blog that embeds line numbers, and now every line starts with 12. or 07 |. Tick Remove existing line numbers and the tool strips a leading number plus one separator from each line: a period, parenthesis, colon, pipe, dash, tab, or space.

One caution: it removes any number at the very start of a line. If your real content has lines that begin with a number, such as 2026 budget, it will strip those too, so check the output before using it.

Common mistakes

Numbering text that will be edited heavily afterward: every insert shifts every number below it, so add numbers last. Using a proportional font and expecting alignment: padding only lines up in monospace fonts. And pasting numbered code back into an editor without stripping the numbers, which breaks the code. Keep the unnumbered original.