Text Diff

What is a text diff?

A diff compares two versions of a text and reports exactly what changed: which lines were added, which were removed, and which stayed the same. It is the mechanism behind every code review, every 'track changes' view, and every version-control history you have ever scrolled through.

Under the hood, a good diff does not simply compare line 1 to line 1. It solves the longest common subsequence problem — finding the largest set of lines that appear in the same order in both versions — and treats everything outside that set as an insertion or a deletion. That is why inserting a paragraph at the top does not mark the entire rest of the document as changed.

Why compare text side by side?

Eyeballing two documents is unreliable: the human eye is very good at reading and very bad at spotting a single altered digit. A diff turns that into a mechanical check.

• Contracts and legal drafts — find the clause the other side quietly edited.
• Code and configuration — see what changed between two versions of a file before deploying.
• Content editing — compare a draft with a copy-edited version and review every change.
• Data and logs — spot the one differing row in two exported lists.
• Translations and manuscripts — track revisions across drafts without version control.

Side-by-side vs unified view

The side-by-side view places version A on the left and version B on the right with aligned rows, so a removed line on the left sits opposite a blank on the right. It is the easiest way to read substantive edits in prose because you keep the full context of both versions.

The unified view is the patch-style format familiar from git: one column, with removed lines prefixed by a minus and added lines by a plus. It is compact, easy to paste into a ticket or an email, and it is the format tools expect. The Nesake Text Diff offers both, and the unified output can be copied to the clipboard in one click.

Ignore options and what they are for

Real-world comparisons are noisy. Two files may be functionally identical but differ in trailing spaces, indentation or letter case, and a strict diff would flag every one of those lines. The ignore-whitespace option trims each line before comparing, so re-indentation and stray tabs stop drowning out real edits. The ignore-case option treats 'Total' and 'total' as identical, which is useful for prose and for case-insensitive data.

Use them deliberately. When you are reviewing code where indentation is significant — Python, YAML, Markdown — leave whitespace comparison on, because a changed indent is a real change. Swapping A and B is also worth knowing about: reversing the inputs turns 'deleted' into 'added' and can make an edit much easier to read.

Supported input and privacy

Paste text directly, or load local files — .txt, .md, .csv, .json, .js, .ts, .html, .css, .xml, .yml, .log and any other plain-text format. There is no length limit beyond your browser's memory, and comparisons of several thousand lines are effectively instant.

Nothing is uploaded. The comparison runs entirely in your browser, which means you can safely diff contracts, credentials, patient data or unreleased source code without it touching a network. Close the tab and the content is gone.

Frequently asked questions