Diff Checker

1. Paste the original text in the left textarea.
2. Paste the modified text in the right textarea.
3. Click "Compare" to see the differences.
4. Added lines are highlighted in green, removed lines in red.

What is a Diff Checker?

A diff checker compares two blocks of text and highlights the differences between them. The term "diff" comes from the Unix diff utility, which has been a foundational tool in software development since the 1970s. Modern diff tools use similar algorithms to detect line-by-line additions, deletions, and modifications. This tool performs the comparison entirely in your browser, making it suitable for comparing source code, configuration files, JSON data, CSV records, or any plain text content.

How Diff Comparison Works

The algorithm splits both inputs into lines and computes the longest common subsequence (LCS) to determine which lines are unchanged, added, or removed. Lines present only in the original text are marked as deletions (shown in red). Lines present only in the modified text are marked as additions (shown in green). Lines that appear in both versions at the same position are left unmarked. This line-by-line approach is the same concept used by Git, SVN, and other version control systems when displaying changes.

Common Use Cases

• Reviewing code changes before committing to version control
• Comparing configuration file versions to find unintended changes
• Verifying that a refactored file produces the same output
• Comparing database export files to detect data changes
• Proofreading document revisions by comparing original and edited versions
• Debugging API responses by comparing expected vs actual output

Tips for Effective Diffing

For the clearest results, make sure both texts use consistent line endings and formatting. Trailing whitespace and inconsistent indentation (tabs vs spaces) can create false differences that obscure the real changes. When comparing structured data like JSON, format both inputs consistently first using a JSON Formatter so that structural changes are clearly visible rather than being hidden by different whitespace. For sorting and deduplicating lists before comparison, use the Line Sort and Deduplicate tool.