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Compare code snippets and show differences.
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Diff Checker compares two blocks of text or code and highlights exactly what changed, added, removed, and unchanged lines, with a similarity score, using the same longest-common-subsequence approach as version-control tools.
That algorithm matters: rather than naively comparing line-for-line, it finds the minimal set of changes, so inserting or deleting a line doesn't throw off everything after it. The result is an accurate, readable diff that pinpoints real edits, which is invaluable for code review, document revisions, and config comparison.
A frequent use is solving the 'these look identical but behave differently' mystery, almost always caused by invisible characters like trailing spaces, tabs versus spaces, or mismatched line endings. A diff makes those visible immediately. The similarity percentage gives a quick sense of scale before you dive into the detail.
Everything runs in your browser, so your code and documents stay private. Pair it with the other ToolsMonk developer and text tools when reviewing changes or reconciling versions.
| Price | Free, no signup, no paywall, no watermark |
|---|---|
| Works on | Any modern browser: desktop, tablet, and mobile |
| Processing | In your browser, files never leave your device |
| Account required | None |
| Category | Developer Tools |
Paste the original on one side and the new version on the other
The tool aligns them and marks added, removed, and unchanged lines
Review the differences and the similarity score
Use it to reconcile or review the two versions
Compares two blocks of text or code and highlights the differences
Line-by-line view of additions, deletions, and unchanged lines
Shows a similarity percentage
Useful for code, documents, and config
Runs in your browser, your input is never uploaded
Free, with no signup and no rate limit
Comparing two versions of code to see exactly what changed
Diffing two documents or config files
Reviewing edits before accepting them
Confirming whether two texts are identical
If 'identical' files differ, check for trailing whitespace, tabs vs spaces, or line-ending mismatches
Use the similarity score for a quick sense of scale before reading the full diff
Put the older version on the left and newer on the right so add/remove reads naturally
Common questions about this tool, its workflow, and what to expect before you use it.
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Open toolWriting a roundup or tutorial? Embed the live Code Diff Checker so readers use it right on your page, or drop in a ready-made card that links to it. Free to use, always.
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Compare code snippets and show differences.
Use Code Diff Checker free →Live tool (iframe)
Readers use the real, working tool right on your page, with a small credit line underneath.
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