📑 Code Diff Viewer

What is a Code Diff Viewer?

A code diff viewer compares two versions of source code and highlights the differences between them. Unlike plain text diff tools, a code diff viewer adds syntax highlighting so you can read the compared code just as you would in your IDE or text editor. Keywords, strings, comments, and numbers are each displayed in distinct colors, making it much easier to understand the context of each change. This tool supports JavaScript, TypeScript, Python, HTML, CSS, JSON, SQL, Go, and Java, covering the most popular programming languages in use today.

The term "diff" originates from the Unix diff command, a utility that has been central to version control and collaborative development since the early 1970s. Modern diff tools build on that foundation by providing richer visual output, including character-level highlighting that pinpoints exactly which characters within a line were changed. This tool implements a variant of the Myers diff algorithm, the same approach used by Git, to produce minimal and accurate diffs. Everything runs entirely in your browser, so your code is never uploaded or stored on any server.

Whether you are reviewing a pull request, debugging a configuration change, auditing a migration, or simply trying to figure out what changed between two versions of a file, this code diff viewer gives you the clarity you need. Three view modes (side-by-side, unified, and inline) let you choose the layout that works best for your workflow. The unified view mimics the standard patch format used by Git and other version control systems, while side-by-side provides a clear two-column comparison. The inline view interleaves deletions and additions for a compact reading experience.

How to Use This Tool

1. Paste your original code into the left "Original" text area and the updated code into the right "Modified" text area. You can paste directly from your editor, clipboard, or file contents.
2. Select the programming language from the dropdown menu. This controls the syntax highlighting applied to the diff output. Choose "Plain Text" if your content is not source code or if your language is not listed.
3. Choose a view mode: Side-by-Side shows both versions in parallel columns, Unified displays a single column with added and removed lines marked by + and - prefixes, and Inline interleaves changes for compact reading.
4. Click "Compare" to generate the diff. Added lines appear in green, removed lines in red, and modified lines show character-level highlighting so you can see exactly which parts changed.
5. Use the "Copy Patch" button to copy the diff in standard unified patch format, suitable for sharing or applying with patch tools. Use "Sample Data" to load a realistic code example and explore the features.

Key Features

• Syntax Highlighting - Code is highlighted with language-aware coloring: keywords in blue, strings in green, comments in gray, and numbers in orange. This makes diffs far easier to read than plain monochrome output.
• Character-Level Diffs - When a line is modified rather than fully added or removed, the tool runs a second-pass comparison at the character level. Changed characters are highlighted with a brighter background so you can instantly spot small edits within long lines.
• Three View Modes - Side-by-side for parallel comparison, unified for Git-style patch output, and inline for a compact sequential view. Switch between them at any time without re-running the comparison.
• Collapsible Context - Unchanged lines are collapsed to show only 3 lines of context around each change. Click the fold markers to expand hidden sections and see the full file.
• Copy as Unified Patch - Export the diff in standard unified patch format that can be shared with teammates, pasted into code reviews, or applied using command-line patch utilities.
• Whitespace and Case Options - Toggle whitespace ignoring to focus on meaningful changes when code has been reformatted. Toggle case ignoring when capitalization differences are not relevant to your comparison.

Frequently Asked Questions

What programming languages are supported?

The syntax highlighter supports JavaScript, TypeScript, Python, HTML, CSS, JSON, SQL, Go, and Java. Each language has its own set of keyword and comment patterns. If your language is not listed, select "Plain Text" to compare without highlighting, or choose a similar language that shares syntax patterns (for example, C# code often highlights well with the Java preset).

How does character-level diff highlighting work?

When the diff algorithm detects that a line was modified (not purely added or removed), it performs a second comparison pass on the content of the old and new versions of that line. This inner diff operates at the character level, identifying the minimal set of insertions and deletions needed to transform one line into the other. The changed characters are then wrapped in highlight spans so you can see exactly what was edited, even in lines with hundreds of characters.

What is the difference between the three view modes?

Side-by-Side places the original and modified files in two columns, aligning matching lines so you can scan left to right. Unified shows a single column with removed lines prefixed by a minus sign and added lines prefixed by a plus sign, matching the format used by Git diff and patch files. Inline interleaves removed and added lines sequentially, giving a compact view that works well on narrow screens or when changes are sparse.

Is my code sent to a server?

No. The entire diff computation, syntax highlighting, and rendering happens in your browser using client-side JavaScript. Your code never leaves your device, which makes this tool safe for comparing proprietary source code, internal configurations, or any other sensitive content.

Can I use this tool for large files?

Yes. The Myers diff algorithm is efficient and handles files with thousands of lines in milliseconds. Context collapsing keeps the output manageable even for large diffs by hiding unchanged regions and showing only the lines surrounding each change. For files with tens of thousands of lines, performance depends on your browser and hardware, but most modern devices handle these sizes without any noticeable delay.