Diff Checker Free - Compare Text Online
Paste two versions of a text and instantly see what changed. Additions, deletions and unchanged lines are highlighted with color coding. Switch between side-by-side and unified views. Line numbers make it easy to find changes. Perfect for comparing code, contracts, essays or any text documents. Everything runs in your browser with no upload.
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When to use it
Spot what changed in a contract draft
Paste each version into "Original" and "Modified" and press "Compare". Added lines are green and removed lines are red, with a summary on top showing how many lines were added, removed or the same.
Check a config file or code change
Paste the old and new settings to see which lines moved. Monospace type and line numbers suit code and config files, and "Swap" flips the original and modified sides.
Review someone's edits to your essay
Pick "Unified" to read the two versions stacked in one column. If the other version has different line breaks around paragraphs, many lines will look changed, so line them up first.
How to use
- Paste the original text in the left box.
- Paste the modified text in the right box.
- Press Compare. Differences are highlighted in green (added) and red (deleted).
How it works
The two texts are split into lines and compared using a longest common subsequence (LCS) algorithm in JavaScript. Added lines are highlighted green, deleted lines red, and unchanged lines stay neutral. Line numbers are shown for both texts. The comparison runs entirely in your browser, so your text is never sent to any server. How to verify. Also available as a free REST API for developers and AI agents (edge-processed, zero retention).
FAQ
How does the comparison work?
The tool splits both texts into lines and finds the longest common subsequence. Lines not in the common sequence are marked as added or deleted.
Can I compare code?
Yes. The comparison is line-based with monospace font, so it works well for code, configuration files and structured text.
Can I compare files?
Paste the contents of two files. Direct file upload comparison is not supported yet.
Is my text uploaded?
No. The comparison runs in your browser using JavaScript. Your text never leaves your device.
Is there a size limit?
There is no hard limit, but very large texts (over 10,000 lines) may be slow.
How is a line with one changed character shown?
The comparison is line by line, so that line appears once as removed (red) and once as added (green). Changed characters inside the line are not highlighted separately.
Can it ignore spaces or letter case?
No. Whitespace and case are compared exactly, so any difference makes the line different. Tidy them yourself before you press "Compare".
What is the difference between "Side by side" and "Unified"?
"Side by side" puts the original and modified text in two columns, "Unified" shows them stacked in one. It is the same result displayed two ways.
Last checked: October 10, 2026 · Dagochim team