Diff Checker
Compare two versions of text, code, JSON, or configuration side by side or inline. Highlight added and removed lines locally, with options to ignore case or whitespace.
This client-side diff tool treats each line as a comparison unit and uses a Longest Common Subsequence (LCS) matrix to align two versions. It helps programmers, editors, and reviewers spot additions, deletions, case changes, and whitespace differences without uploading the pasted text for processing.
LCS Line Comparison and Change Alignment
O(N × M) Dynamic-Programming ComparisonThe tool uses a Longest Common Subsequence comparison to align matching lines and mark additions and deletions. It operates in the browser without uploading the pasted content for comparison.
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How the Diff Checker Works
Follow these simple steps to get accurate results instantly.
Paste Original Text
Enter or paste the source text, original code, or base document into the 'Original Text' editor on the left.
Paste Changed Text
Paste the updated, revised, or modified text snippet into the 'Changed Text' editor on the right.
Select Diff Mode
Choose a side-by-side split view or a unified inline view, then decide whether the comparison should ignore case or whitespace differences.
View Visual Difference
Click 'Find Difference' to see added content highlighted in green and removed content marked in red with full statistics.
Longest Common Subsequence (LCS) Comparison Method
Changed Lines = Added Lines + Removed Lines
The diff algorithm searches for the Longest Common Subsequence (LCS) between the two sequences of lines. Unmatched original lines are classified as deletions and unmatched revised lines as additions. Optional normalization can ignore case or repeated whitespace before the sequences are compared.
Example Calculation
Input: Original: 'DevCalc is fast.' | Changed: 'DevCalc is fast and free.'
Output: The original line is marked removed and the revised line is marked added.
Common Uses
- • Comparing source code revisions and git merge conflicts
- • Tracking editorial revisions in essays, contracts, and articles
- • Validating configuration file changes (JSON, YAML, ENV)
- • Checking SQL schema updates and API payload changes
- • Finding subtle typo corrections across long text documents
Frequently Asked Questions
Verified answers to essential calculation and diagnostic questions.
No. DevCalc's Diff Checker processes all text comparison logic 100% locally within your browser using client-side JavaScript. No documents, code, passwords, or confidential texts are transmitted, logged, or stored on any server.
Side-by-Side (Split) view displays the Original text on the left and the Changed text on the right, keeping corresponding lines visually aligned. Unified (Inline) view combines both versions into a single continuous stream, placing removed lines and added lines sequentially with +/- markers, similar to standard Git commit diffs.
Yes. You can toggle the 'Ignore Whitespace' option to focus strictly on semantic text changes rather than formatting differences (such as tabs vs spaces or trailing spaces).
The tool compares content line by line and offers Side-by-Side and Unified result views. You can also ignore letter case or normalize whitespace. For small wording edits, review the highlighted changed lines to locate the exact revision.
Compare Two Texts or Code Snippets Online
Paste the original version on the left and the revised version on the right to create a clear line-by-line diff. Added lines appear in green, removed lines appear in red, and unchanged lines remain aligned for context. Use the split view when you want both versions beside each other, or the unified view when you want a compact, Git-style change list.
When to Ignore Whitespace or Letter Case
Enable Ignore Whitespace when tabs, repeated spaces, or leading and trailing spaces are not meaningful to the review. Enable Ignore Case when capitalization should not count as a change. Leave both options off when comparing source code, YAML, environment files, or other formats where spacing or capitalization may alter behaviour.
Useful Diff Checker Workflows
- Code review: compare a function before and after refactoring without opening a repository.
- Configuration checks: find changed values in JSON, SQL, INI, or environment templates.
- Editorial review: compare two drafts of an article, email, policy, or assignment.
- Debugging: isolate a missing line, renamed key, or unexpected generated output.
Privacy and Comparison Limits
The comparison runs in your browser and does not require an account. This is a text comparison tool, not a parser: it does not validate whether pasted code compiles or whether JSON and YAML are syntactically valid. Avoid pasting production secrets into any webpage, and rotate a credential immediately if it has already been exposed elsewhere.
Written & maintained by Aditya Singh
Aditya Singh is a software engineer and the founder of DevCalc, based in Uttar Pradesh, India. He builds and maintains every tool on this site with careful attention to accuracy and user experience. Read more about the author →