Free online diff checker. Compare two texts side by side, highlight additions, deletions, and modifications. Perfect for developers, writers, and content creators.
Comparing texts with our diff checker is simple and fast:
The diff checker uses a professional-grade algorithm to find the minimum set of changes needed to transform one text into another:
Diff checking is an essential skill for software developers, technical writers, and anyone who works with evolving documents. In software development, comparing configuration files, source code changes, or database schemas helps identify unintended modifications before they cause problems. Version control systems like Git use sophisticated diff algorithms internally, but having a standalone tool is invaluable for quick comparisons outside of a repository. For technical writers and content creators, diff checkers reveal subtle changes between document drafts — whether it's a reworded sentence, a moved paragraph, or an added section. Legal professionals use diff tools to spot clause changes between contract versions. Even everyday users benefit when comparing edited documents, email revisions, or policy updates. The key advantage of a browser-based diff checker is privacy — your documents never leave your device, making it safe for sensitive materials.
Beyond basic line-by-line comparison, understanding diff algorithms helps you get better results. The longest common subsequence (LCS) algorithm used by professional diff tools finds the optimal alignment between texts, minimizing the number of reported changes. This means fewer false positives compared to naive character-by-character comparison. When comparing code files, pay attention to whitespace-only changes — some diff tools offer options to ignore trailing whitespace or treat tabs and spaces equivalently. For large files, consider normalizing the text first by removing comments or formatting differences if you only care about logical changes. When comparing configuration files, grouping related settings together before comparison makes the diff output much easier to read. For documents with heavy restructuring, look at the change statistics — a high deletion count combined with a high addition count suggests significant rewriting rather than minor edits.
Our diff checker uses a dynamic programming approach based on the Longest Common Subsequence (LCS) algorithm. This is the same fundamental approach used by professional tools like GNU diff and Git. The algorithm finds the optimal alignment between the two texts, minimizing the total number of insertions and deletions needed to transform one text into the other. This produces cleaner, more meaningful diffs compared to simpler approaches.
Yes! The diff checker works excellently with code files including JavaScript, Python, HTML, CSS, JSON, YAML, XML, and any other text-based format. It compares line by line, so structural changes in code are clearly visible. Note that it treats each line as a unit — if a single line is modified, the entire line is marked as changed rather than highlighting individual character differences within the line.
Yes, the diff checker supports all Unicode text including Vietnamese with diacritical marks (dấu). Since it operates on complete lines rather than individual characters, accented characters are handled correctly. Both Vietnamese and English text can be compared simultaneously without issues.
The diff checker processes everything locally in your browser, so performance depends on your device. It handles files up to approximately 50,000 lines smoothly on modern devices. For very large files, we recommend splitting them into smaller sections for comparison. The processing happens entirely client-side, so there's no server upload time regardless of file size.
Currently the tool displays all differences in a unified view. You can select and copy specific changed lines from the diff output. For bulk operations, you can also copy the entire diff result which includes context lines along with the changes, making it easy to share with collaborators.
While Git diff is excellent for version-controlled repositories, our browser-based diff checker requires no setup, no repository, and no command-line knowledge. It works instantly for any two texts — even ones that were never tracked in version control. It's perfect for quick ad-hoc comparisons, comparing documents from different sources, or when you don't have access to a terminal.