Diff Checker

What is an online diff checker?

An online diff checker compares two blocks of text or code and highlights every line that was added (green) or removed (red). It shows exactly what changed between two versions without needing git or any version control software installed.

How does the diff algorithm work?

This tool uses the Longest Common Subsequence (LCS) algorithm — the same core method used by git diff and GNU diff. It finds the largest set of lines that appear unchanged in both texts, then marks everything else as an addition or removal.

What is a .diff file and unified diff format?

Unified diff is a standard patch file format recognised by git, SVN, and code review tools. Lines starting with + are additions, lines with − are deletions, and @@ markers show the line ranges of each changed block (hunk). You can apply a .diff file to a codebase with git apply or the patch command.

What is the difference between unified view and split view?

Unified view shows both versions interleaved in one column with +/− symbols — good for reading all changes in sequence. Split view places Original on the left and Changed on the right in two parallel columns, pairing related lines side by side for easier comparison.

Is my data safe when using this diff checker?

Yes. All comparison processing runs locally in your browser using JavaScript. No text is ever sent to any server. Your code, credentials, and private content remain completely on your device.

How large can the input files be?

The tool handles texts up to approximately 500 lines per side without performance issues. For larger diffs, the LCS computation slows significantly. For very large code files, git diff in the terminal handles files of any size efficiently.