Free Online Diff Checker

Why use Diff Checker

• Color-coded additions and deletions let you scan hundreds of lines and spot every change in seconds.
• Toggle between unified and side-by-side views depending on how you like to read diffs.
• Ignore-whitespace and ignore-case options filter out formatting noise so you only see real content changes.

How it works

The diff checker implements a variant of the Myers diff algorithm, which finds the shortest edit script (minimum number of insertions and deletions) to transform the original text into the modified text. It splits both inputs into lines, then builds an edit graph where moving right represents a deletion and moving down represents an insertion. The algorithm traces the shortest path through this graph using a breadth-first approach. When ignore-whitespace is enabled, each line is normalized by collapsing all whitespace to single spaces and trimming before comparison, but the original formatting is preserved in the output display. When ignore-case is active, both sides are lowercased for comparison purposes only. The summary counts are derived from the edit script by tallying insertions, deletions, and unchanged lines.

About this tool

Compare two config files side by side after a deploy goes wrong. Paste the old version on the left, the new one on the right, and additions show green, deletions show red. Toggle between unified and side-by-side views depending on whether you want a compact summary or a spatially aligned comparison. Ignore-whitespace and ignore-case options filter out formatting noise so you only see meaningful content changes. Git's built-in diff is tied to version-controlled files. The terminal `diff` command works but gives you raw output without color. Diffchecker.com uploads your text to their servers. This one runs the Myers diff algorithm in your browser -- nothing leaves your machine, which matters when you're comparing credentials files or proprietary code.

How to use Diff Checker

1. Paste both versions. Drop the original into the left panel and the modified version into the right.
2. Review the diff. Additions show green, deletions show red. Toggle between unified and side-by-side views.
3. Filter noise. Turn on ignore-whitespace or ignore-case to focus on meaningful content changes.

Use cases

• A deploy just went sideways. Compare the old nginx.conf backup against the current one to find exactly which lines changed.
• You're reviewing two drafts of API documentation and need to find every sentence that changed between the first draft and the editor's revision.