Code Diff Checker

Green lines are additions — present in the modified code but not the original. Red lines are deletions — present in the original but removed. Yellow lines are modifications — a line was changed (the algorithm detected the old and new version of the same line). Unchanged lines appear in normal style for context. The statistics bar shows totals for each category.

The tool uses an LCS (Longest Common Subsequence) algorithm like git diff. If a line was substantially changed, the algorithm may classify it as a deletion (red) of the old version plus an addition (green) of the new version, rather than a single modification (yellow). Minor changes to similar lines are typically detected as yellow modifications. This matches how standard diff tools work.

When enabled, any sequence of spaces and tabs is treated as a single space before comparison. Lines that differ only in indentation or extra spaces are classified as identical. This is very useful for comparing code that was reformatted — for example, comparing code before and after running a code formatter like Prettier or Black.

The tool analyzes the syntax of your pasted code and identifies the likely programming language — JavaScript, Python, PHP, CSS, HTML, JSON, SQL, and 10+ more. The detected language label appears above the input. You can override it manually from the language dropdown. Language detection does not affect the diff algorithm; it only controls syntax context labeling.

Yes. The tool works on any plain text including JSON, YAML, TOML, INI, XML, and Dockerfile content. For JSON, use the Ignore Whitespace option to ignore formatting differences and focus on content changes. For comparing large config files, the split view makes it easy to spot missing or added keys.

Swap exchanges the Original and Modified code panels. All additions become deletions and vice versa. Use this if you pasted the code in the wrong order — instead of re-pasting, just swap and compare again.

No. The entire comparison runs in your browser using JavaScript. Your code, configuration files, or any text you paste never leaves your device.