Diff Checker Online - Compare Text

How Text Diffing Works

A diff finds the minimal set of changes (insertions and deletions) that transform one text into another. The classic algorithm — Myers diff, used by Git — finds the longest common subsequence (LCS) of the two texts, then marks everything not in the LCS as added or removed.

The output format you know from Git (+ for added, - for removed) is the unified diff format, standardized in POSIX. It's the same format used in patch files, pull requests, and code review tools.

🛠️ When to Use a Diff Checker

• Comparing config files: spot which environment variable or setting changed between prod and staging.
• Reviewing generated code: compare a scaffold or migration output before committing it.
• Document revisions: track changes between two drafts of a spec, README, or email.
• Debugging API responses: paste two JSON responses to see exactly which fields changed.
• Sensitive content: unlike cloud-based diff tools, this one processes everything locally — safe for internal configs, credentials, or proprietary code.

📊 Reading the Output

• Green lines — present in the new version but not the old (added).
• Red lines — present in the old version but not the new (removed).
• Gray lines — unchanged context lines that appear in both.

A "changed" line is represented as a removal followed by an addition — diffs don't have a "modified" operation, only delete + insert pairs. Word-level diffing (intra-line highlighting) makes small changes easier to spot in long lines.

All comparison runs locally in your browser. Your text is never sent anywhere.