About Diff Checker
The Diff Checker compares two texts side-by-side and highlights every line that was added, removed, or changed. Added lines are shown in green, removed lines in red, and unchanged lines in neutral. This makes it instantly clear what changed between two versions of any text.
This tool is useful for comparing code revisions, checking edits in documents, reviewing configuration file changes, comparing data exports from different time periods, and spotting changes in content.
The comparison is line-by-line, using the longest common subsequence (LCS) algorithm to minimize the diff and show the most accurate set of changes.
Everything runs locally in your browser. Your data never leaves your device.
How to Use Diff Checker
Paste the original text in the left panel.
Paste the modified text in the right panel.
Added lines are shown in green, removed lines in red, unchanged lines in neutral.
Use the unified or split view toggle for different display modes.
Frequently Asked Questions
Does it diff character by character or line by line?
It diffs line by line at the top level, showing which lines were added, removed, or changed between the two texts.
Can I compare code files?
Yes — paste code from any language into the two panels and differences are highlighted immediately.
What algorithm is used?
The longest common subsequence (LCS) algorithm, which is the same approach used by Unix diff and most version control systems.
Does it compare the content character by character within changed lines?
Yes — changed lines show inline word-level or character-level highlights to pinpoint exactly what changed within a line.
Can I use this to compare two versions of a document?
Yes — paste the old version on the left and the new version on the right to see every change highlighted.
Is there a size limit?
No hard limit. The tool handles large texts in your browser, though very large files (100,000+ lines) may slow down the comparison.