Diff Checker — Free Online Text & Code Comparison

The Unified Diff format is the industry-standard method for representing changes between two text files. It is the default output format for Git (`git diff`) and the GNU `diff` utility. Instead of showing the entire text of both files side-by-side, a unified diff outputs a single, consolidated block of text. It uses a three-line context window around each change to help developers understand where the modification occurred. Lines starting with a minus sign (`-`) in red represent text that was deleted from the original file, while lines starting with a plus sign (`+`) in green represent text that was added to the new file. Unchanged lines have no prefix and serve as contextual anchors. Our online diff checker visualizes this unified format, making it incredibly easy to review pull requests, audit code, or track document revisions.

Under the hood, our online diff checker uses the Longest Common Subsequence (LCS) algorithm combined with Myers' diff algorithm. This is the exact same mathematical foundation used by Git. The algorithm works by finding the longest sequence of characters or lines that appear in both the original and modified text in the same order. By identifying this common backbone, it can accurately isolate the exact insertions and deletions. This makes it highly efficient for comparing massive codebases, JSON files, or large plain-text documents line-by-line.

Yes, it is 100% safe. Unlike many free diff viewers online that upload your text to their servers for processing, our code difference tool is fully client-side. The LCS algorithm runs entirely within your browser's JavaScript engine. Your proprietary code, API keys, and sensitive documents never leave your local machine, ensuring enterprise-grade data privacy during your code reviews.