Add Line Numbers
Prefix every line with a sequential number — pick the start, step, separator, and alignment. Runs in your browser; nothing is uploaded.
About this tool
Add Line Numbers prefixes every line of your text with a sequential
number — the same job as nl or cat -n, but right in your browser.
- Start number — the number given to the first line (default
1). Use any whole number, including0or a negative value. - Step — the increment between consecutive numbers (default
1). Set it to10for10, 20, 30…. - Separator — the text placed between the number and the line content. It
defaults to a tab; type
.,:,|, or anything you like. - Number alignment — spaces right-aligns the numbers so they line up
(
9,10), zeros pads them (09,10), and none leaves them as-is. - Skip blank lines — like
cat -b, blank (whitespace-only) lines are left untouched and don't consume a number.
Everything runs locally in your browser via WebAssembly — your text is never uploaded.
Handy for
- Numbering a snippet of code or a list for reference in review comments.
- Producing
1.,2.,3.style ordered lists from plain lines. - Turning a plain log or checklist into a numbered one.
FAQ
Can numbering start at 0 or a negative number?
Yes. Start number accepts any whole number, including 0 and negatives, so
you can produce 0, 1, 2… or -2, -1, 0…. Only the step is restricted: it
must be at least 1 (a step of 0 or a negative step is rejected with an
error). Alignment still works with negative starts — the minus sign counts
toward the column width.
How do I get 10, 20, 30 style numbering?
Set Start number to 10 and Step to 10. The first line gets 10,
the second 20, and so on. Any start/step combination of whole numbers works,
e.g. start 100, step 5 gives 100, 105, 110….
What is the difference between the spaces, zeros, and none alignments?
They control how numbers are padded to a common column width, which is the
width of the largest number in the output. Spaces right-aligns ( 9,
10), zeros left-pads with zeros (09, 10), and none writes each number
as-is (9, 10), so columns may not line up past line 9.
How does "skip blank lines" treat lines that contain only spaces?
With Skip blank lines enabled (the cat -b behavior), any line that is
empty or contains only whitespace is passed through unchanged — it gets no
number and doesn't consume one, so the next non-blank line continues the
sequence. The result also reports how many of the total lines were numbered.
Developer & Automation Access
Run it from the terminal
Same engine as this page, headless — via the gizza CLI:
gizza tool add-line-numbers "Paste text to number…"New to the CLI? Get gizza →
Open it by URL
Pre-fill and auto-run this tool with query parameters — the names match the API/CLI:
https://gizza.ai/tools/add-line-numbers/?text=Paste%20text%20to%20number%E2%80%A6&start=1&step=1&separator=tab&pad=spaces&number_nonblank=trueMachine-readable descriptor: tool.json — title + parameters JSON Schema for agents.