Diff Viewer (Side-by-Side)
Compare two code files or text blocks online for free. Our diff viewer highlights additions in green and removals in red with a side-by-side split view or unified diff mode. Supports any plain text format — code, JSON, YAML, Markdown, SQL, and more. No signup required.
Paste or upload two text blocks to compare them. Choose between a side-by-side split view or a unified diff view with color-coded additions and removals.
Why Use Our Diff Viewer?
Side-by-side and unified diff comparison with color-coded highlighting
Split View & Unified View
Our diff viewer gives you two display modes: a side-by-side split view that shows original and modified text in parallel columns, and a unified view that interleaves additions and removals in a single scrollable list. Switch between modes instantly with one click.
Instant Diff Comparison
The diff viewer processes your text blocks instantly in the browser using an LCS-based algorithm. Get color-coded additions, removals, and unchanged lines with line numbers, similarity percentage, and changed block count — all in under a second.
Secure Diff Viewer Online
All comparison runs entirely in your browser. Your code, config files, and text blocks are never uploaded to any server when you use our diff viewer online — 100% private, works completely offline once loaded.
Diff Viewer — No Installation
Use our free diff viewer directly in your browser with no downloads, no plugins, and no account required. Supports any plain text format — code, JSON, YAML, Markdown, SQL, and more. Download the result as a .patch file for version control workflows.
Common Use Cases for Diff Viewer
Practical applications for side-by-side text and code comparison
Code Review
Compare two versions of a function, class, or module side by side before submitting a pull request. Our diff viewer highlights every addition and removal so reviewers can focus on what changed, not what stayed the same.
Config File Comparison
Spot differences between environment configs, YAML files, JSON settings, or .env files instantly. Use our diff viewer to catch accidental changes before deploying to staging or production.
API Response Debugging
Compare two API responses side by side to find unexpected field changes, missing keys, or value drift between environments. Our diff viewer works with any plain text format including JSON and XML.
Documentation Editing
Compare draft and final versions of documentation, README files, or Markdown content to review editorial changes. The diff viewer shows exactly which sentences were added, removed, or left unchanged.
Database Migration Scripts
Diff two SQL migration scripts to verify that only the intended changes are present before running them against a production database. Our diff viewer supports any plain text file format.
Release Validation
Compare build artifacts, lockfiles, or generated output between two release versions to catch unintended regressions. Download the .patch file from our diff viewer for inclusion in release notes or audit logs.
Understanding the Diff Viewer
Learn how the diff algorithm works and how to read the output
What is a Diff Viewer?
A diff viewer is a tool that compares two versions of a text file or code block and highlights the differences between them. Our diff viewer uses the Longest Common Subsequence (LCS) algorithm — the same algorithm underlying git diff — to identify which lines were added (shown in green), removed (shown in red), and unchanged (shown in white). The result is displayed in either a side-by-side split view or a unified view, both with line numbers for easy navigation.
How Our Diff Viewer Works
- Paste or Upload Your Text: Enter the original version in the left panel and the modified version in the right panel. You can paste text directly or upload any plain text file — code, JSON, YAML, Markdown, SQL, and more are all supported.
- Instant Browser-Based Comparison:Click "Compare" and the LCS diff algorithm runs entirely in your browser. The comparison table, similarity score, and changed block count are computed locally — your text never leaves your device.
- View, Copy, or Download the Result: Switch between split view and unified view with one click. Copy the unified diff to your clipboard or download it as a
.patchfile for use in version control workflows.
How to Read the Diff Output
- Green lines (additions): Lines that exist in the modified version but not in the original. In split view they appear in the right panel; in unified view they are prefixed with
+. - Red lines (removals): Lines that exist in the original but were deleted in the modified version. In split view they appear in the left panel; in unified view they are prefixed with
−. - White lines (unchanged): Lines that are identical in both versions. These provide context around the changes so you can understand what was modified.
- Similarity percentage: The ratio of unchanged lines to total lines, expressed as a percentage. A score of 100% means the inputs are identical; lower scores indicate more differences.
Important Limitations
The diff viewer compares text line by line — it does not perform word-level or character-level diffing within a line. Very large files (tens of thousands of lines) may be slow to process due to the O(n×m) complexity of the LCS algorithm. For best performance, compare files under 5,000 lines each. The ignore whitespace option normalizes leading and trailing spaces but does not collapse internal whitespace within a line.
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Frequently Asked Questions About Diff Viewer
Common questions about text comparison, diff algorithms, and output formats
A diff viewer is a tool that compares two versions of a text file or code block and highlights the differences — additions in green, removals in red, and unchanged lines in white. Our diff viewer runs entirely in your browser using an LCS algorithm, with both side-by-side split view and unified view modes.
Our diff viewer supports any plain text format — JavaScript, TypeScript, Python, Lua, JSON, YAML, XML, HTML, CSS, Markdown, SQL, Go, Rust, Java, C#, C/C++, Ruby, PHP, shell scripts, and more. Any file that can be opened as plain text can be compared.
Split view shows the original and modified text in two parallel columns side by side, making it easy to see the full context of each version. Unified view interleaves additions and removals in a single column, prefixed with + and −, similar to the output of git diff. Both views use the same color coding.
Yes. All comparison runs entirely in your browser using pure JavaScript. Your code, config files, and text blocks are never uploaded to any server. Everything stays completely private on your device every time you use our diff viewer online.
The similarity percentage is the ratio of unchanged lines to total lines, expressed as a percentage. A score of 100% means the two inputs are identical. A score of 0% means every line is different. It gives you a quick sense of how much has changed between the two versions.
Yes. Click "Download .patch" to save the unified diff output as a .patch file. This file is compatible with standard patch tools and can be applied with git apply or the patch command. It is also useful for including in release notes or audit logs.
When "Ignore leading/trailing whitespace" is enabled, the diff viewer trims spaces and tabs from the start and end of each line before comparing. This means lines that differ only in indentation are treated as identical. It is useful for comparing code that has been reformatted.
The diff viewer works well for files up to a few thousand lines each. Very large files (tens of thousands of lines) may be slow due to the O(n×m) complexity of the LCS algorithm. If you hit a size limit, the tool will show an error message. For very large files, consider comparing specific sections rather than the full file.
Yes! Our diff viewer is 100% free with no signup, no account, and no usage limits. Compare as many text blocks as you need — completely free, forever.