ORIGINAL
Paste the original code
MODIFIED
Paste the modified code
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Paste code in both panels and click Compare// compare code side by side and highlight every change
Compare two code blocks side by side and instantly highlight every addition, deletion, and change. Free browser-based code diff tool, no sign-up needed.
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Paste code in both panels and click CompareEnter the original version of your code in the left panel.
Enter the updated or modified version in the right panel.
Click Compare to see all additions, deletions, and unchanged lines highlighted.
Code Diff Viewer computes the line-by-line difference between two code blocks using the LCS (Longest Common Subsequence) algorithm — the same approach used by Git. Additions are highlighted in green, deletions in red, and unchanged lines in neutral — all processed entirely in your browser.
Code Diff Viewer works with any plain-text code — JavaScript, Python, PHP, CSS, HTML, SQL, YAML, JSON, and more. It compares line by line regardless of language syntax.
Split view shows original and modified code side by side, making it easy to see both versions simultaneously. Unified view shows a single stream with added lines marked + and removed lines marked −, similar to a standard git diff output.
No. All diffing is computed entirely in your browser. Your code never leaves your machine, making this tool safe for sensitive or proprietary code.
When enabled, lines that differ only in leading/trailing spaces or indentation are treated as equal. This is useful when comparing code that has been reformatted or re-indented.
Yes. Click the "Download .diff" button to save the unified diff as a standard .diff file, which is compatible with git apply and most patch tools.
This tool uses the LCS (Longest Common Subsequence) algorithm, which is the foundation of git diff and most professional diff tools. It finds the minimal set of changes between two sequences of lines.
A Code Diff Viewer is a tool that compares two versions of a file or code block and visually highlights what has changed. It shows you which lines were added, which were deleted, and which remained the same — making it indispensable for developers reviewing changes, debugging regressions, or understanding the impact of a patch.
JLV Code Diff Viewer runs entirely in your browser with no server upload required. Whether you're comparing JavaScript functions, CSS rules, configuration files, or SQL queries, the diff is computed instantly using a proven algorithm and presented in a clean, readable format.
Under the hood, code diffing relies on the Longest Common Subsequence (LCS) algorithm. Given two sequences of lines — original and modified — the algorithm identifies the longest sequence of lines that appear in both files in the same order. Everything not in that common sequence is either an insertion (new in modified) or a deletion (removed from original).
This is exactly how git diff works. The LCS approach guarantees the minimal edit distance: it finds the smallest number of additions and deletions needed to transform one file into the other. The result is a precise, low-noise diff that highlights only genuine changes.
Two presentation modes serve different purposes:
− and highlighted red; added lines are prefixed with + and highlighted green. This is the classic git diff format and is the output format understood by patch and git apply.Code diff tools are useful in a surprising number of everyday developer scenarios:
nginx.conf, docker-compose.yml, or .env files between environments to spot unintended differences..patch or .diff file and applied to another codebase using standard Unix tools.The visual conventions used in this tool follow the universal diff standard:
The stats bar at the top of the results shows a quick summary: the number of additions, deletions, and unchanged lines — giving you an at-a-glance sense of how large the change set is.
Many developers work with sensitive code: API keys, business logic, database schemas. JLV Code Diff Viewer processes everything client-side in your browser. Nothing is transmitted to any server. You can safely diff proprietary code, credentials files, or internal configuration without any risk of data exposure.
Two optional filters help reduce noise in the diff output:
Once you've compared your code, you can copy the unified diff to your clipboard using the "Copy Unified" button, or download it as a .diff file. The downloaded file follows the standard unified diff format and is compatible with patch, git apply, and most code review tools.
Git diff is powerful but requires a repository and command-line access. This browser-based tool is useful when you don't have a git history — for example, when comparing two files you received by email, two snippets from Stack Overflow, or two versions of a config you manually edited. It's also faster for quick one-off comparisons where setting up a git repo would be overkill.