Diff Checker

How to Use the Diff Checker

1. Paste your original text — Enter or paste the before-version of your text into the "Original Text" textarea on the left. This could be the old version of a document, a previous code snippet, or any baseline text you want to compare against.
2. Paste your modified text — Enter or paste the after-version into the "Modified Text" textarea on the right. This is the new or updated version that you want to compare against the original.
3. Configure options — Enable "Ignore Whitespace" if indentation or trailing spaces should not count as differences. Enable "Ignore Case" if capitalization differences should be ignored during comparison.
4. Click Compare — Press the Compare button to generate a line-by-line diff. The results appear below with color-coded highlighting: green for added lines, red for removed lines, and no highlight for unchanged lines.
5. Review stats and results — Check the summary badges showing lines added, removed, unchanged, and total changes. Use Copy Diff to copy the unified diff to your clipboard, or Swap to reverse the comparison direction.

Features

• Line-by-line diff using Longest Common Subsequence (LCS) algorithm
• Color-coded output: green for additions, red for deletions, no highlight for unchanged
• Unified diff format with +, -, and space prefixes for each line
• Ignore Whitespace option to skip indentation and trailing space differences
• Ignore Case option for case-insensitive text comparison
• Stats summary: lines added, removed, unchanged, and total changes
• Swap button to quickly reverse original and modified texts
• Copy Diff button to copy the unified diff to your clipboard
• Side-by-side input layout on desktop, stacked layout on mobile
• Line numbers in the diff output for easy reference
• 100% client-side processing — your text never leaves your browser
• Handles thousands of lines efficiently in the browser

Understanding Diff Comparison

Common Use Cases

Diff Checker Tips

• After identifying differences between two text versions, use Text Replacer to batch-fix common patterns across the modified text, such as standardizing terminology or formatting.
• Use Word Counter on both the original and modified text to get a quick overview of length changes before running a detailed line-by-line comparison.
• If your diff shows many duplicate unchanged lines cluttering the output, use Remove Duplicate Lines tool on each text first to strip out repeated content, then re-run the diff for a cleaner result.
• After comparing texts and merging changes, use Text Sorter to alphabetize sections, reorder paragraphs, or organize lines by length for a cleaner final document.
• When comparing code with different indentation styles, enable Ignore Whitespace to focus on actual logic changes rather than formatting differences.
• For lists with inconsistent capitalization (e.g., names from different data sources), enable Ignore Case to see past casing differences and focus on content differences.
• Use the Swap button when you need to see the reverse perspective — it swaps which text is treated as 'original' and which as 'modified', useful for reviewing what was removed versus what was added.
• The Copy Diff button copies the output in standard unified diff format, which you can paste into emails, documentation, or issue trackers to share exact change details with your team.

Best Practices

• Trim trailing whitespace from both texts before comparing if you only care about content differences, or simply enable the Ignore Whitespace toggle to handle this automatically.
• When comparing code files, make sure both versions use the same line ending style (LF vs. CRLF). Mixed line endings can cause every line to appear as changed. Use our Text Replacer to normalize line endings first.
• For very large files with thousands of lines, the comparison may take a few seconds. The LCS algorithm has O(n×m) complexity, so the time scales with the product of both file sizes.
• If the diff output seems too noisy, try enabling both Ignore Whitespace and Ignore Case to filter out formatting and casing differences and focus on substantive content changes.
• Use the Copy Diff feature to save a snapshot of the differences for your records. The unified diff format is universally understood and can be referenced in code reviews, documentation, or changelogs.
• When comparing translated or localized content, paste both versions and enable Ignore Case to catch differences that might be hidden by inconsistent capitalization across languages.