Code Diff Viewer

The Code Diff Viewer compares two pieces of code or text side by side, highlighting added, removed, and modified lines with syntax coloring for programming languages. Developers review diffs constantly: code reviews in pull requests, understanding what changed between versions, debugging differences between environments (development vs production configs), comparing two solutions to a problem. A good diff viewer makes these comparisons fast and clear.

Paste two code snippets or text blocks and the tool renders a side-by-side diff with additions highlighted green, deletions red, and unchanged context in neutral color. Syntax highlighting auto-detects the language (JavaScript, Python, Go, Ruby, CSS, HTML, JSON, SQL, and many more). Toggle between side-by-side and unified view. Word-level diff within changed lines highlights exactly which characters differ. Ignore whitespace and case-insensitive options help when formatting differences are noise. All comparison runs client-side — proprietary code stays in your browser.

Diff algorithm: most diff tools use variants of Myers algorithm (1986) or the similar LCS (Longest Common Subsequence) approach. The algorithm finds the minimal sequence of additions and deletions to transform one text into another.

Line-level diff: compare text line by line. Lines that exist only in A are deletions; only in B are additions; in both (same position) are unchanged. Simple and fast but may show unnecessary changes when lines were reordered.

Word-level diff: after finding changed lines, break them into words and diff within the line to highlight exactly what characters differ. Useful for seeing fine-grained changes.

Character-level diff: same idea but at character granularity. Very precise but noisy for most practical use.

Unified diff format: standard Git/Unix diff output. Shows context lines with changes marked + or -:

@@ -1,3 +1,3 @@
context line
-removed line
+added line
context line

Side-by-side diff: visual layout with original on left, modified on right. Easier to read for most users; takes more horizontal space.

Whitespace handling:
- Strict: every space and newline matters
- Trim whitespace: strip leading/trailing per line
- Ignore whitespace: diff treats whitespace-only changes as equal
- Normalize: collapse multiple spaces to one before diffing

Case sensitivity: option to treat uppercase and lowercase as equal, useful for comparing code where case doesn\u2019t affect meaning (some older languages, SQL keywords).

Move detection: sophisticated diff tools detect when blocks moved between files. Simple line diff shows moves as delete + add pairs. Move-aware diff shows moves as a single operation.

Syntax highlighting: applied to both original and modified text using language-specific highlighters (Prism, Highlight.js). Auto-detection uses common patterns (#! shebang, import statements, typical keywords).

Performance: diff of two 10,000-line files takes 100-500ms in browser depending on similarity. Very different files are faster to diff than similar ones (paradoxically — the algorithm has more work when sequences are mostly similar).

Compared to git diff on the command line, this tool provides visual side-by-side view with syntax highlighting. CLI is better for scripting and version control; this tool for interactive visual comparison.

Compared to VS Code\u2019s diff view, this tool doesn\u2019t require files on disk. VS Code wins for comparing checked-in files; this tool for ad-hoc pasted comparisons.

Compared to other online diff tools (diffchecker.com, etc.), this tool has better syntax highlighting and more language support. Features are similar; UI and language coverage vary.