What This Tool Does
This text diff tool compares two blocks of text line-by-line and highlights which lines are identical, added, removed, or changed. Useful for comparing document versions, code snippets, configuration files, or contract revisions.
Inputs Explained
- Original Text: The first version of the text.
- Modified Text: The second version. Differences are calculated relative to the original.
How It Works
The tool splits both texts into lines and uses a longest common subsequence algorithm to identify matching lines. Lines that exist in only the original are marked as removed; lines only in the modified version are marked as added; matching lines are unchanged.
Formula / Logic Used
Text Diff Checker
Compare any two texts and see exactly which lines were added, removed, or changed.
Step-by-Step Example
Original:
Hello world This is line two End of file
Modified:
Hello world This is updated line two A new line added End of file
Result: 1 unchanged, 1 removed, 2 added (line two changed = 1 remove + 1 add).
Use Cases
- Document version comparison: Compare two drafts of a contract, article, or report to spot edits.
- Code review: Quickly diff two versions of a code snippet without setting up Git.
- Configuration file changes: See exactly what changed between server config or environment files.
- Translation review: Compare two translation versions of the same source text.
- Plagiarism quick check: Compare a submission against a reference text to identify copied passages.
Assumptions and Limitations
- Diff is line-based. Two lines that differ by one word are shown as one removal + one addition, not as a partial match.
- Performance is O(n×m) — comparing two 10,000-line texts may be slow on older devices.
- No syntax highlighting. For source code, use Git or a dedicated code-diff tool.
- Whitespace differences (trailing spaces, tab vs space) count as differences. Normalize first if needed.
Frequently Asked Questions
How does the diff algorithm work?
It uses a longest common subsequence algorithm — the same family of algorithms behind Git diff, Unix diff, and Word's track changes. It finds the maximum overlap between two line sequences and marks the rest as added or removed.
Can I compare more than two texts?
This tool compares two at a time. For 3-way merges (typical in source control), use Git or a merge tool like Beyond Compare or Meld.
Are whitespace and case differences shown?
Yes. Any character difference counts as a change. If you want to ignore whitespace or case, normalize both texts first using the case converter or trim trailing spaces.
Is my text uploaded anywhere?
No. Both texts are processed locally in your browser. Nothing is sent to any server, logged, or stored. You can use this tool offline once the page loads.
What's the maximum text size?
Practical limit is around 10,000 lines per side on a modern device. Above that, the comparison may take several seconds. The tool is optimized for normal documents and code files.
Can I see word-level differences within a line?
This version shows line-level diff. Word-level (intra-line) diff is a more complex algorithm; for that, look at GitHub's pull request view or specialized diff tools.
How is this different from Word's compare documents?
Word can compare formatted documents and track every formatting change. This tool compares plain text only and is much faster for code, config files, or any unformatted content.
Can I export the diff result?
Use your browser's Print → Save as PDF to capture the colored diff output. The result section is fully styled for printing.
Sources and References
- Wikipedia — Longest Common Subsequence — The algorithm family behind text diffing.
- Wikipedia — Diff utility — History of the Unix diff command.
- Git Documentation — Diff — How Git implements text comparison.
- MDN — String split() — Reference for the line-splitting used internally.