Diff Checker
Compare two texts side by side and find differences instantly
Enter text in both fields and click Compare to see differences.
About Diff Checker
The Diff Checker is a free online tool that compares two blocks of text and highlights the differences between them. It performs a line-by-line comparison using a Longest Common Subsequence (LCS) algorithm, the same foundational technique used by professional version control systems like Git. Whether you are reviewing code changes, comparing document revisions, or verifying configuration file updates, this tool makes it easy to spot exactly what was added, removed, or left unchanged.
Text diffing is a fundamental operation in software development and content management. When two versions of a file exist, a diff algorithm identifies the minimal set of changes needed to transform one version into the other. Lines present only in the original are marked as removals (highlighted in red), lines present only in the modified version are marked as additions (highlighted in green), and lines that appear in both are shown as unchanged. This visual approach lets you quickly scan large documents and focus only on what changed.
How It Works
This tool splits both inputs into lines, then computes the Longest Common Subsequence (LCS) of those lines. The LCS represents the largest set of lines that appear in both texts in the same order. Any line not in the LCS is either an addition or a removal. The result is displayed in a side-by-side view with line numbers, making it straightforward to match corresponding sections. You can also enable the "Ignore whitespace" option to focus on meaningful content changes while filtering out formatting differences like extra spaces or trailing whitespace.
Common Use Cases
- Code review: Compare two versions of source code to see exactly which lines were modified before merging changes.
- Document comparison: Check differences between drafts of contracts, articles, or reports to track edits.
- Configuration auditing: Verify changes to server configs, environment files, or deployment scripts.
- Debugging: Compare expected output with actual output to pinpoint discrepancies in test results.
- Content migration: Ensure content was transferred correctly between systems by comparing source and destination.
FAQ
Q: Is my text stored or sent to a server?
A: No. All comparisons happen entirely in your browser using JavaScript. Your text never leaves your device, ensuring complete privacy.
Q: What algorithm does this tool use?
A: It uses a Longest Common Subsequence (LCS) based diff algorithm, similar to what Git and other version control systems use. This produces accurate, minimal diffs by finding the largest set of matching lines between the two texts.
Q: Is there a size limit for the text I can compare?
A: There is no hard limit, but very large texts (tens of thousands of lines) may take a moment to process since the comparison runs in your browser. For most practical use cases, results appear instantly.
Q: What does the "Ignore whitespace" option do?
A: When enabled, the tool trims leading and trailing whitespace from each line and collapses multiple consecutive spaces into one before comparing. This helps you focus on actual content changes rather than formatting differences.
Q: Can I compare code files with this tool?
A: Yes. The tool uses a monospace font and preserves indentation, making it well-suited for comparing source code, JSON, XML, configuration files, and any other structured text.