Text Diff
Text diff is the quickest way to see exactly what changed between two versions of text. Unlike a general comparison tool, this diff utility focuses on producing a clean, minimal difference output that shows you the precise edits -- nothing more, nothing less. It uses the same algorithm that powers Git diff and other version control systems, optimized to find the smallest set of changes that transforms one text into another. Whether you are a developer reviewing code changes, an editor tracking document revisions, or a writer comparing draft versions, this tool gives you a clear, unambiguous view of what was added, removed, and left unchanged.
What Is
Text diff is based on the Myers diff algorithm or similar longest common subsequence (LCS) algorithms. These algorithms find the minimum number of edits needed to transform one text into another, producing what is called the shortest edit script. The result is a list of operations: insert (add text), delete (remove text), and equal (unchanged text). This is fundamentally different from a simple side-by-side comparison -- diff produces a merged view that shows the original text with changes inline. The algorithm is optimal in the sense that it finds the fewest possible edits, which means the output is as concise as possible. This is why Git and other version control systems use it: developers can see exactly what changed without wading through unchanged content. The tool supports both unified diff format (compact, showing context around changes) and split view (side by side).
How to Use
- Enter the original text in the first field and the changed text in the second field.
- Select your preferred output format: unified diff for compact output or split view for side-by-side.
- Click Generate Diff to compute the differences between the two texts.
- Review the output: deletions marked with minus signs or red, additions with plus signs or green.
- Copy the diff output for use in code review, documentation, or version tracking.
Examples
Input: Old: Hello World, New: Hello There World
Process: LCS algorithm then detect insertions and deletions
Result: Hello +There World (inserted There)
Input: Old: color centre, New: color center
Process: Character-level diff then highlight spelling change
Result: center (American spelling) marked as change
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Frequently Asked Questions
What is the difference between text-diff and text-compare-tool?
Text-diff focuses on producing a minimal, precise edit script -- the smallest set of changes between two texts. It is optimized for showing exactly what was added and removed in a compact format. Text-compare-tool focuses on visual side-by-side comparison with highlighting. Use diff when you want a concise change summary; use compare when you want a visual overview of differences.
Why does the diff sometimes show changes that seem larger than expected?
The diff algorithm finds the mathematically minimum set of edits, but this does not always match human intuition. If you move a paragraph from the end to the beginning, the diff might show it as a deletion at the end plus an addition at the beginning, rather than a move. This is normal -- diff algorithms detect insertions and deletions, not moves.
Can I use text-diff for languages other than English?
Yes, the diff algorithm works on any text regardless of language. It operates on characters and words, not language-specific features. However, for languages that do not use spaces between words (like Chinese or Japanese), word-level diff may not work as expected. Use character-level comparison for those languages.
What is unified diff format?
Unified diff is a compact format that shows changes with a few lines of context around each change. It uses plus signs (+) for additions and minus signs (-) for deletions. This format is widely used in software development for code reviews and patches. If you have ever seen a GitHub pull request, you have seen unified diff format.
Can I generate a patch file from the diff output?
The diff output can be used as input to patch tools if it is in a compatible format. Standard unified diff output can be applied using the Unix patch command. This is useful for applying code changes across different versions of files. Check that your output matches the expected patch format for your specific use case.