Diff Checker
Compare two blocks of text or code and highlight differences
About Diff Checker
Compares two blocks of text or code and highlights exactly what's different between them, line by line.
Paste your two versions of the text into the two panels, and the differences are highlighted automatically.
This is useful well beyond code — comparing two drafts of a document, or two versions of a contract, works the same way and is often faster than manually reading both side by side.
Watch: Diff Checker in Action
- Is this only useful for comparing code?
- No — it's useful well beyond code. Comparing two drafts of a document, or two versions of a contract, works the same way and is often faster than manually reading both side by side.
- How do I compare two text files online?
- Open each file in a text editor, copy its contents, and paste one version into the left panel and the other into the right. The differences are marked straight away: added lines, removed lines and changed lines, with the changed words highlighted inside each changed line.
- How does a diff checker work?
- It lines up the two versions and finds the longest run of lines they have in common, then marks everything outside that run as added or removed. Lines that were reworded are then compared word by word, so you can see exactly which words were edited rather than just that the line differs.
- Can I see which words changed inside a line, not just which lines?
- Yes. When a line was edited rather than replaced outright, the individual words that differ are highlighted within it, which makes small edits such as a changed number or a swapped name easy to spot.
- Is there a size limit when I compare text?
- Very large inputs are capped at about 3,000 lines per side so the page stays responsive. If you hit the limit, compare the section you care about instead of the whole document.
How to use Diff Checker
A diff checker compares two versions of the same text and shows exactly what changed: lines that were added, lines that were removed, and, inside a changed line, the individual words that differ. Developers use it to review code edits; writers, editors and anyone handling contracts or policies use it to check a revised draft against the original. Paste both versions side by side and the result appears at once. Text Similarity Checker is the better fit when you want an overlap percentage instead of a line-by-line view.
Paste your first version of the text or code into the left panel and your second version into the right panel. The differences are highlighted automatically, line by line — added lines, removed lines, and changed lines are each marked distinctly so you can quickly scan for exactly what changed between the two versions without manually reading through both side by side looking for differences yourself.
When to use it
The most direct use is comparing two versions of code — checking exactly what changed between a working version and a new edit before committing, or reviewing someone else's proposed change line by line. It's equally useful well beyond code: comparing two drafts of a document or contract to see exactly what was edited, checking a revised email against the original before resending, or verifying that a "find and replace" operation in a large document only changed what you intended it to.
When not to use it
For comparing entire files or folders with many files at once (a real codebase's full set of changed files across a whole commit, for instance), a version-control system's own diff view or a dedicated file-comparison tool built for that scale is more practical than pasting file contents in one pair at a time. If what you actually need is to merge two versions together (combining changes from both rather than just seeing what differs), that's a related but different operation — a merge tool, not a diff viewer, is built for that.
Tips for best results
For comparing longer documents, it can help to paste in smaller, focused sections rather than an entire long document at once — a shorter comparison is faster to visually scan for the specific differences you're actually looking for, especially if most of the document is unchanged and only a small section is genuinely different.
Limitations
Comparison is line-by-line text matching — it doesn't understand the semantic meaning of code or prose, so a change that reorders content without altering its meaning (moving a paragraph, or reordering function arguments in a way that doesn't change behavior) will show as a difference even though the practical result may be equivalent.
Privacy
Both texts are compared entirely in your browser — neither version of your text or code is uploaded to any server, which matters in particular for comparing code or documents you wouldn't want leaving your device.
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