Text Compare & Diff Tool
Text Compare & Diff is an intuitive tool that quickly finds the differences between two pieces of text. Paste the original text on the left and the revised text on the right; the tool aligns the lines one by one and computes the longest common subsequence to mark every change precisely: removed content on the left is highlighted in red, added content on the right in blue, and unchanged lines stay as they are. The two panes sit side by side, each taking half the width, with line numbers and character counts always visible, so even long documents are easy to scan for changes. Ideal for code review, copy editing, contract comparison, log analysis and translation checking. Either pane can be copied with one click, and the whole comparison can be downloaded as an image with the site logo for archiving and sharing. Clean and beautiful UI with light/dark themes and 12 languages, fully local and private — a handy little helper for document collaboration and version comparison.
What is it
A diff tool lines two texts up row by row, first finding the lines both sides share (the longest common subsequence), then splitting the gaps between them into "removed" and "added": lines that appear only on the left are marked red, lines only on the right are marked blue. Common lines stay as they are and line numbers always refer to each side's own original text.
Notes & fun facts
Changes between versions always need explaining. Developers check what a commit really changed, editors proof two drafts, legal teams compare old and new contract clauses, translators verify their work against the source. The red and blue side-by-side marks leave no addition or deletion hidden.
Origin & history
The computer concept of "diff" was born in the early 1970s: the Unix diff command compared files with the longest common subsequence algorithm and printed a change list, becoming a cornerstone of software engineering. This web page's line-by-line view runs on the same mathematics, just rendered as a clearer red-and-blue side-by-side view.
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