Text Difference Checker guide
Compare two versions line by line and identify added, removed, and unchanged lines with a bounded local algorithm.
What this tool does
The Text Difference Checker splits both inputs at line boundaries and calculates a longest common subsequence. Lines in that shared ordered sequence are marked unchanged. Lines present only in the original are marked removed, and lines present only in the revision are marked added. Original and revised line numbers are displayed in separate columns.
Comparison is exact and case-sensitive. A line with one changed space, punctuation mark, or letter is represented as one removed line followed by one added line. The tool does not perform word-level highlighting or ignore whitespace automatically.
The algorithm is intentionally limited to 400 lines in each input. Longest-common-subsequence comparison uses time and memory related to both line counts, so the limit protects the browser from an unexpectedly expensive comparison. Split larger documents into logical sections.
How to use it
- Paste the earlier version into Original text.
- Paste the later version into Revised text.
- Select Compare lines.
- Review green additions, red removals, and muted unchanged lines.
- Return to the source documents before accepting or publishing changes.
Keep comparable content aligned into meaningful lines. A paragraph stored as one long line will be treated as one complete unit even if only one word changed.
Benefits
- Uses an ordered line comparison rather than unordered matching
- Displays old and new line numbers
- Summarizes added, removed, and unchanged counts
- Enforces a clear browser-safety limit
- Keeps both drafts on the current device
What a line diff cannot prove
A diff shows representation changes, not whether they are correct. An unchanged statement can still be false, outdated, inaccessible, or inappropriate. A removed qualification can materially change meaning even when the edit looks small. Formatting, different line endings, wrapping, and generated files can also create noisy results.
Use source control or a document review system when you need author identity, timestamps, comments, approvals, conflict resolution, or a durable audit history. This browser tool does not save versions or establish who made a change.
For contracts, policies, code, regulated material, and other high-impact documents, review the complete context with appropriate specialists.