What is a diff checker and how does it work?

A diff checker compares two text files or code blocks to show their differences. It uses algorithms to analyze each line, highlighting what was added, removed, or modified between versions.

How do I read diff output - what do red and green colors mean?

Green (or lines with +) indicate additions in the modified version, while red (or lines with -) show deletions from the original. Gray or white lines are unchanged.

Is my data stored or transmitted?

No. All processing happens entirely in your browser using JavaScript. No data is ever transmitted to any server. The tool works fully offline once loaded.

Can I use diff checkers to compare code files?

Absolutely! Diff checkers are perfect for comparing code files in any programming language. Use options like ignore whitespace to focus on actual code changes rather than formatting differences.

What is the difference between side-by-side and unified view?

Side-by-side shows original and modified text in parallel columns. Unified shows changes in a single column with + and - prefixes, similar to git diff output.

Is there a limit to how much text I can compare?

There is no hard limit - you can compare files of any size your browser can handle. However, very large files may take longer to process. We recommend files under 5,000 lines each for optimal performance.

What does Ignore whitespace do?

When enabled, the comparison treats multiple spaces, tabs, and other whitespace as equivalent. This is useful when comparing code where indentation may differ.

Can I share my diff with others?

Yes. The URL updates automatically with your content. You can also export the diff as a .patch file or copy it to clipboard in unified diff format.

What is word-level diff?

Word-level diff highlights individual word changes within lines, rather than marking entire lines as changed. This is helpful when you've made small edits to long lines of text.

What diff algorithm does this tool use?

This tool uses the Longest Common Subsequence (LCS) algorithm, the same approach used by git diff and other professional diff tools.

Diff Checker
Compare Text & Code

Compare text and code with side-by-side or unified diff views. See exactly what changed between two versions. 100% client-side. Zero data stored.

Original Text

Drop file here

Modified Text

Drop file here

Insertions

Deletions

Unchanged

Ignore whitespace Ignore case Ignore blank lines Word-level diff

Diff Output

Enter text in both panels and click Compare to see the diff

Common Use Cases

Code Reviews

Compare code changes before and after refactoring. Perfect for reviewing pull requests and understanding what changed in each commit.

Document Comparison

Compare versions of documentation, contracts, or legal documents to identify exactly what changed between drafts.

Configuration Files

Compare JSON, YAML, XML, or .env files to troubleshoot configuration changes and environment differences.

Debugging

Compare API responses, log files, or stack traces to identify what changed when a bug was introduced.

SQL & Queries

Compare database queries or SQL scripts to understand performance improvements or schema migrations.

Content Updates

Track changes in website content, blog posts, or marketing copy to ensure edits are accurate and complete.

Frequently Asked Questions

Why We Built Diff Checker

Developers spend hours comparing code versions, reviewing pull requests, and debugging configuration changes. Most online diff tools send your code to external servers - a serious security risk for proprietary code, API keys, or sensitive data.

Unlike online tools that send your data to external servers, Diff Checker processes everything locally using JavaScript. This means your sensitive data never leaves your computer. The tool works completely offline once loaded, making it safe for enterprise environments and air-gapped systems.

Diff Checker is part of RJL.io's collection of free developer tools - each designed to do one thing exceptionally well, with no accounts, no tracking, and no data collection. Check out our other tools: UUID Generator, QR Code Generator, Base64 Encoder, and more. Every tool is 100% client-side, works offline, and respects your privacy.

Diff Checker Compare Text & Code