About this tool
Two versions of a config file, two drafts of a clause, two prompt iterations — somewhere in the middle something changed, and reading both side by side is the slowest way to find it. Text Diff Checker compares two blocks of text line by line and highlights exactly what was added, what was removed and what was modified, using a longest-common-subsequence pass that keeps the alignment sensible even when blocks moved around. Removed lines show in red, added lines in green, and changed pairs line up so a one-word edit does not look like a full rewrite. Paste into either side and the diff updates immediately — there is no compare button to press and, more importantly, no upload: contracts, credential files and unpublished drafts stay on your machine, which is precisely what makes a browser-based diff preferable to the well-known online alternatives for anything confidential. Use it to review a colleague's edits to a document, to check what a code generator changed in your config, to compare API responses across environments, or to proof your own rewrite against the original. A summary line counts additions, removals and modifications so you can gauge the size of a change at a glance. For structured data, pretty-print both sides first and the line diff becomes a field-by-field comparison.
How to use Text Diff Checker
- Paste the original text into the left box and the revised text into the right box.
- The diff renders live: red lines were removed, green lines added, amber pairs modified.
- Read the summary counts of additions, removals and changes above the diff.
- Copy the diff view or the unified text summary for sharing.
Frequently asked questions
Is my text uploaded?
No. The comparison runs entirely in your browser with a local longest-common-subsequence algorithm. Nothing is transmitted — safe for contracts, configs and drafts.
Does it compare words or lines?
Lines. Line-level diffing is what makes config files, code and prose drafts readable; adjacent removed and added lines are paired so small edits show as modifications.
Is there a size limit?
The full LCS algorithm handles a few thousand lines per side comfortably. Beyond that the tool falls back to a fast prefix/suffix comparison so the page stays responsive.
Can I ignore whitespace differences?
The current comparison is exact, line by line. Trim or normalize the text first — for example with the transcript cleaner or your editor — if whitespace-only changes are noise for your use case.