Text Diff

What is a text diff?

A diff (short for difference) is a side-by-side report of what changed between two pieces of text. The classic use is in version control — Git, SVN and friends use diffs to show what each commit modified — but the same idea is useful for proofreading edits, comparing legal contracts, spotting small changes in configuration files, or checking that a document survived a copy-paste round-trip intact. This tool computes the diff using a longest-common-subsequence algorithm, the same family of techniques that power git diff.

How to use this tool

Paste the original version into A and the modified version into B. The diff appears live below: green lines (or words) are additions in B, red are deletions from A, plain rows are unchanged. Switch between line and word granularity depending on what you want to see — line diffs are best for code or structured text, word diffs are easier to read for prose where small wording changes matter. Stats above the output show counts of added, removed and unchanged tokens.

When to use line vs word diff

Line diff is the right default for code, JSON, CSV, log files and anything where structure lives at the line level. A single character change shows up as a removed line and an added line — easy to scan, and matches what version control tools do. Word diff shines for prose: it highlights the actual words that changed inside a paragraph, so you can see edits without re-reading the whole text. Avoid word diff on very long documents — the LCS computation gets quadratic and starts to feel slow above a few thousand words.

Frequently asked questions