HTML / Text Diff Tool

Paste your original version into the 'Before' box and the updated version into the 'After' box, then click Compare. The tool runs a line-by-line comparison and highlights every difference: added lines in green, removed lines struck through in red, and unchanged lines in grey. You also get a quick count of how many lines were added, removed, and left unchanged.

Yes. The comparison runs entirely in your browser using JavaScript, so the text you paste is never uploaded to a server or stored anywhere. That makes it safe for unpublished page copy, internal HTML, or anything confidential. Nothing leaves your machine, and refreshing the page clears it.

A line-by-line diff treats each line as the smallest unit, so if you change a single word, the whole line is marked as removed and re-added rather than highlighting just that word. This tool works line by line, which keeps HTML and structured text easy to scan because changes line up cleanly. For very long single-line content, break it onto multiple lines first so the diff can pinpoint changes more precisely.

The tool uses a longest-common-subsequence algorithm to find the smallest set of real changes, but that comparison is capped at roughly 400 lines on each side for performance. Above that, it falls back to showing every original line as removed and every new line as added rather than computing a precise match. To stay within the accurate range, compare smaller sections or focus on the specific block of HTML you care about.

This tool is great for one-off, manual comparisons when you already have both versions in front of you. If you want to catch ongoing changes, SiteGauge can monitor any URL automatically and show you a clean before/after diff each time the page changes, along with an AI summary of what moved. That removes the need to grab and paste snapshots yourself.