Adding line numbers to text is a fundamental task across programming, legal documentation, academic writing, and technical publishing. Whether you are preparing a code snippet for a pull request review, formatting a legal transcript with mandatory line numbering, or creating numbered reference material for a classroom, this tool provides instant, customizable line numbering without any software installation.
The Add Line Numbers tool is a browser-based utility that prepends sequential numbers to every line of your input text. Unlike basic text editors that only display line numbers on screen, this tool embeds the numbers directly into the text content — making them visible when the text is copied, printed, or shared. You control the starting number, separator character, padding format, and whether blank lines receive numbers.
Core capabilities include custom start numbers for mid-file snippets, configurable separators (period, colon, tab, pipe, or custom strings), automatic zero-padding for alignment in large documents, blank line skip options, and real-time preview. The tool handles Unicode text, mixed-language content, and preserves all original formatting including indentation and special characters.
When you paste text into the input area, the tool splits it by line breaks (handling both Unix LF and Windows CRLF formats). It then iterates through each line, calculates the appropriate padding width based on the total line count, and prepends the formatted number with your chosen separator. The output updates in real-time as you modify settings, so you see exactly what the final text will look like before copying.
Software developers use line numbering when sharing code in documentation, emails, or chat where the recipient's editor may not show line numbers. Legal professionals add line numbers to depositions, transcripts, and court filings as required by court formatting rules. Technical writers number steps in procedures. Educators number lines in poetry or prose excerpts for classroom discussion references. Data analysts number CSV rows for quick identification during manual review.
Manual line numbering is tedious and error-prone — a single insertion or deletion throws off every subsequent number. Text editors like Notepad++ show line numbers on screen but do not embed them into the text for sharing. Word processors can add line numbers but require navigating multiple menu layers. This tool provides one-click numbering with full customization, and because it runs entirely in your browser, your text is never uploaded to any server.
Developers doing code reviews, legal assistants formatting court documents, teachers preparing annotated literary passages, technical writers creating numbered procedure steps, and anyone who needs to reference specific lines in shared text. If you have ever said 'look at line 23' in an email and wished the recipient could actually see line 23, this tool is for you.
Paste any text into the input field. The default settings (start at 1, period separator, auto-padding) work for most use cases. Adjust the start number if your text is a mid-file excerpt, change the separator if you prefer colons or tabs, and copy the numbered output. The entire process takes under 5 seconds.
Use tab separators when the numbered output will be imported into a spreadsheet. Use zero-padding when documents exceed 99 lines to maintain column alignment. For legal documents, verify your jurisdiction's specific line numbering requirements (some require numbering every 5th line). When numbering code, match the starting number to the actual file line to avoid confusion during reviews.
The tool numbers lines based on line break characters — it does not perform word-wrap numbering. Very long single lines will receive one number regardless of how they display on screen. For documents requiring word-wrap-aware numbering (like court transcripts with strict lines-per-page rules), a dedicated legal formatting tool may be more appropriate.
Yes. You can set any starting number. This is especially useful when numbering a code snippet that starts at line 47 in the original file, or when continuing numbering across multiple document sections.
Common separators include period (1. text), colon (1: text), tab (1\ttext), pipe (1 | text), and right parenthesis (1) text). You can also define a custom separator string.
Yes. For a 200-line document, numbers are automatically padded to three digits (001, 002... 200) so every line aligns perfectly. This is critical for monospaced code and legal documents.
Yes. You can choose to skip empty lines during numbering while preserving them in the output, which is useful for code blocks where blank lines separate logical sections.
Absolutely. Legal transcripts and court filings often require continuous line numbering. You can set numbering every 5th line (5, 10, 15...) which matches standard legal formatting requirements in many jurisdictions.
The tool processes text entirely in your browser using optimized string operations. Files with 10,000+ lines are handled smoothly without any server round-trip or upload delay.
Yes — this is one of the most common use cases. When sharing code snippets in emails, Slack, or documentation, adding line numbers lets reviewers reference specific lines (e.g., 'see line 34') without ambiguity.
Yes. The tool only prepends the line number and separator to each line. All original whitespace, indentation, tabs, and special characters remain exactly as entered.