How to use the Text Diff Checker

Paste the original text on the left and the modified text on the right.
Click Compare to see a line-by-line diff.
Lines in green were added; lines in red were removed; unchanged lines appear in grey.

How the diff algorithm works

This tool uses the Longest Common Subsequence (LCS) algorithm to compute the minimum edit distance between two texts. The algorithm finds the largest set of lines that appear in both texts in the same order, then marks everything not in the common sequence as either added or removed.

The comparison is line-by-line, a single character change in a line marks the entire line as removed and re-added. Leading and trailing whitespace on each line is preserved.

Common use cases

Code review: compare two versions of a function or configuration file
Document editing: see what changed between a draft and a revised version
Translation review: compare original and translated texts side by side
Legal and compliance: identify changes between contract versions
API responses: compare JSON or XML responses across test runs
Database exports: spot differences in SQL dumps or CSV exports

Reading the diff output

Green lines (+): lines present in the modified text but not in the original (added)
Red lines (−): lines present in the original but not in the modified text (removed)
Grey lines: lines unchanged between both versions

A modified line typically appears as one red line (the old version) followed by one green line (the new version).

Privacy

All comparison runs in your browser. No text is sent to any server.