Number every line with a custom start, step, and separator — aligned in a column.
Prefix each line with a number using a custom start value, step, and separator (1. / 1) / 1: / tab). Numbers align in a neat column, can be zero-padded, and blank lines can be skipped and uncounted. Runs entirely in your browser.
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Whenever people need to refer to specific lines: code samples in documentation, quoting a contract clause in review comments, marking up a script or transcript, or giving a colleague a precise reference in a log file. It turns "the bit near the middle" into something unambiguous.
It keeps the text aligned. Without padding, line 9 and line 10 start at different columns, so the left edge of your content zigzags once you pass single digits. Padding to a fixed width keeps everything in a clean column, which matters for anything monospaced.
Yes, and it is useful when you are numbering an excerpt. Quoting lines 240 to 260 of a file is far more helpful if the numbers match the original rather than restarting at 1. The step setting also lets you number every fifth line, as printed scripts and legal documents often do.
Yes, Add Line Numbers is completely free. No signup, no account, and no watermark on outputs. A Pro tier is available for 100 AI ops/day and larger file sizes.
Add Line Numbers runs entirely in your browser. Your file is never uploaded — it is read, processed and saved locally, so it never reaches our servers or anyone else's. You can disconnect from the internet after the page loads and it still works.
Separator
Aligned numbering: When padding is on, every number is right-aligned to the same width, so the separators form a clean vertical column even past line 9, 99, or 999.
Skip blank lines: Turn this on to leave empty lines unnumbered — and, importantly, uncounted — so the numbering reflects only lines with content.
Flexible start and step: Begin at 0 or any offset and count by any step, for line references, ordered lists, numbered scripts, or CSV row labels.
Privacy: Runs entirely on plain JavaScript in your browser. Your text is never sent to a server and the tool works offline.