Text Difference Checker

What Is the Text Difference Checker?

The Text Difference Checker compares two blocks of text side-by-side and highlights every addition and deletion using an LCS (Longest Common Subsequence) algorithm — the same method used by Git and standard diff utilities. Switch between Line Diff mode (whole lines highlighted) and Word Diff mode (individual word changes highlighted within lines) for different levels of granularity. Windows and Unix line endings are normalised automatically so cross-platform pastes always compare correctly.

How to Use the Text Diff Tool

1. Paste Original Text (A) — this is your baseline version.
2. Paste Modified Text (B) — the version you want to compare against.
3. Choose mode — Line Diff is faster and clearer for large changes; Word Diff shows exactly which words changed within each line.
4. Enable options — Ignore Case treats uppercase/lowercase as equal; Ignore Leading Whitespace ignores indentation differences.
5. Copy Diff — exports a unified diff format with + / - / two-space line prefixes compatible with patch files and GitHub comments.

Where Can You Use the Text Difference Checker?

Diff Modes and Comparison Options

• Line Diff — highlights entire lines as added (green) or removed (red). Fast and easy to read for large structural changes.
• Word Diff — runs a second LCS pass within each changed line pair to highlight exactly which words differ. Best for catching minor edits within mostly-similar lines.
• Ignore Case — converts both texts to lowercase before comparison. The diff view still shows original-case text; only the comparison logic changes.
• Ignore Leading Whitespace — trims the start and end of each line before comparing. Useful for comparing code with different indentation styles.
• Copy Diff — exports a unified diff format: removed lines prefixed with - , added lines with + , unchanged with two spaces.
• Swap — swaps Text A and Text B with one click to reverse the direction of the diff.
• 2,000-line guard — inputs are capped at 2,000 lines each to prevent browser slowdown on very large files.

Best Practices and Limitations

The LCS algorithm has O(m×n) time complexity where m and n are the line counts. For texts under 500 lines each, diffs are near-instant. For very large files (thousands of lines), Word Diff mode may take 1–2 seconds since it runs a second LCS pass per changed line pair.

Binary or encoded content: Base64 data, minified JavaScript, or binary-encoded content will produce valid diffs, but the output will be difficult to read. This tool is designed for human-readable text.

Large code files: For files with thousands of lines, consider using a dedicated tool like git diff or vimdiff which stream changes incrementally rather than computing the full LCS at once.