Diff Checker
Compare two blocks of text and see exactly what changed, line by line.
Comparing two versions of a document, a config file, or a piece of code by reading them side by side is slow and error-prone — the human eye is bad at spotting a single changed word buried in otherwise identical paragraphs. A diff checker automates that comparison, showing exactly which lines were added, removed, or left unchanged between two pieces of text.
This tool computes a line-by-line diff using a longest common subsequence algorithm, the same underlying approach used by tools like git diff, which finds the minimal set of insertions and deletions needed to transform the original text into the modified text. Unchanged lines are shown in the neutral color, added lines are highlighted in green with a leading +, and removed lines are highlighted in red with a leading -, giving you an immediate visual sense of how much actually changed.
The comparison runs entirely in your browser as you edit either text box, so you can iterate on a document and watch the diff update live rather than re-running a comparison manually each time.
How to use Diff Checker
- 1
Paste the original text
Enter the baseline version in the left text box.
- 2
Paste the modified text
Enter the updated version in the right text box.
- 3
Review the diff
Added lines appear in green with a +, removed lines in red with a -, unchanged lines are shown as-is.
Features
- Line-by-line comparison using an LCS-based diff algorithm
- Live updates as you edit either text
- Clear visual distinction between additions and deletions
- Handles documents up to several thousand lines smoothly
Frequently asked questions
Common mistakes to avoid
- Assuming identical-looking lines with different invisible whitespace (tabs vs spaces) will show as unchanged — this tool compares lines exactly, including whitespace.
- Comparing text with different line ending conventions (Windows CRLF vs Unix LF), which can cause every line to appear changed.
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