Diff Checker

The Diff Checker compares two text documents and highlights the differences line by line. Useful for proofreading (comparing two drafts of an article), legal document review (identifying changes between contract versions), data validation (ensuring export matches expected output), and anywhere you need to see what changed between two pieces of text. While the Code Diff Viewer focuses on programming code with syntax highlighting, this tool is optimized for plain prose, configuration files, data outputs, and general text.

Paste two text versions into the left and right panels; see changes highlighted immediately. Added lines show green, removed lines red, modified lines get word-level highlighting showing exactly which characters differ. Options to ignore whitespace, case, or punctuation for focusing on meaningful changes. Side-by-side and unified view modes available. Handles texts up to tens of thousands of lines with smooth performance. All comparison runs locally so confidential documents stay in your browser.

Diff algorithm overview is in the Code Diff Viewer entry. This tool uses the same core algorithm but with tuning for prose and general text:

Word-level focus: prose rarely cares about exact character-level differences. Word diff is usually the right granularity.

Sentence boundaries: for prose comparison, you may want to diff at sentence level (one block per sentence). The tool offers sentence-level diff for document comparison.

Case insensitivity: often important for prose comparison where \"The\" and \"the\" are practically equivalent.

Punctuation normalization: optional. Some documents have typographic quote differences (straight vs curly) that shouldn\u2019t be treated as meaningful changes.

Paragraph alignment: long documents may have paragraphs that shifted in position. Paragraph-aware diff tries to align paragraphs before diffing within each.

Text length limits: optimized for up to 100,000 lines of text per side. Browser memory is the limit beyond that.

Comparison modes:
- Line-by-line: default, good for most documents
- Word-by-word: treats entire text as a sequence of words, ignoring line breaks
- Character-by-character: very fine granularity, mostly for small texts

Whitespace options:
- Ignore trailing whitespace: common preference
- Ignore all whitespace: collapse all whitespace to one space before diffing
- Ignore blank lines: treat blank lines as equal regardless of position

Output formats:
- Side-by-side visual with highlighting
- Unified text diff with context lines
- Only differences (skip unchanged context)
- Summary statistics (X lines added, Y lines removed, Z lines modified)

Performance optimizations:
- Short common prefix/suffix detected and skipped
- Identical large blocks identified without detailed diffing
- Virtual scrolling for long results

Compared to Code Diff Viewer, this tool is for plain text without syntax highlighting. Use Code Diff Viewer for programming source code; use this one for prose, legal documents, and general text.

Compared to Track Changes in Word or Google Docs, this tool works on static snapshots without needing a shared document. Track Changes is for ongoing collaboration; this tool for snapshot comparison.

Compared to command-line diff, this tool has a visual side-by-side UI. CLI is better for scripting; this tool for interactive review.