A diff checker answers one question fast: what changed between two versions of a text? Paste the original into the left box and the revised version into the right, and this free online diff checker highlights every addition, deletion and modification — character by character, word by word, or line by line. It runs entirely in your browser, so even confidential drafts never leave your device.
Diffs are the same comparison that programmers use in Git and code review, but you don’t need any technical setup here. Writers compare essay drafts, translators check a translation against its source, and anyone who’s been sent “the final version” twice can verify the two files really are identical.
Worked example: one changed clause, two views
Take two versions of a contract paragraph where only one clause changed. Version A:
The contractor shall complete all work within thirty (30) days of signing. Payment of fifty percent (50%) is due upon delivery of materials. The remaining balance shall be paid within fourteen (14) days of final inspection.
Version B is identical except one clause — the balance is now due within seven (7) days instead of fourteen:
The contractor shall complete all work within thirty (30) days of signing. Payment of fifty percent (50%) is due upon delivery of materials. The remaining balance shall be paid within seven (7) days of final inspection.
Run both through the tool above and compare the two views:
- Line mode shows the whole third line marked as changed — perfect for scanning a long document and jumping straight to the altered lines. You see at a glance that line 3 differs; lines 1–2 are untouched.
- Word mode zooms into line 3 and highlights only the changed words:
fourteen (14)seven (7) — everything else on the line is shown as identical. This is the view for reading exactly what was altered, word by word.
Which view to use: line mode when you want to find where changes are in a long document; word mode when you want to read what each change actually says. Most reviews start in line mode and switch to word mode on the interesting lines.
What you can use a diff checker for
- Finding what changed in a config file: paste the old and new versions to see exactly which settings were edited before you deploy.
- Comparing essay drafts: see what your editor or tutor actually changed instead of re-reading the whole document.
- Reviewing a translation against its source: line up the source and the translation (or two translation drafts) to confirm nothing was skipped or duplicated.
- Verifying two “identical” documents: when someone sends “final_v2” after “final”, a diff proves in seconds whether anything actually changed.
- Checking pasted code or data: compare two CSV exports, JSON blobs or log snippets to find the one row that differs.
Honest limitations
- A line-based diff struggles when paragraphs are re-wrapped — if one version has different line breaks, the diff may flag whole paragraphs as changed even though only the wrapping moved. Normalise line breaks first, or use word mode.
- This is not a merge tool and has no Git awareness: it shows differences, it won’t combine two versions or resolve conflicts.
- Very large documents slow the browser down, since the comparison runs on your device. For files of many thousands of lines, a desktop diff tool will be faster.
- Whitespace-only differences (tabs vs spaces, trailing spaces) can clutter results — that’s what the “ignore whitespace” option is for (see the FAQ).
Frequently asked questions
What is a diff?
A diff (short for “difference”) is a line-by-line or word-by-word comparison of two texts that shows exactly what was added, removed or changed between them. It is the standard way programmers review code changes, and the same idea works for any text.
Side-by-side or unified view — which should I pick?
Side-by-side shows the old text on the left and the new text on the right, which is easiest to read on wide screens. A unified view interleaves changes into a single column, which is more compact. For a quick visual review, side-by-side usually wins; for copying the result into a report, unified is tidier.
What does “ignore whitespace” change?
It tells the diff to treat differences in spaces, tabs and line endings as irrelevant. Turn it on when the only changes are formatting — for example, when one file uses tabs and the other uses spaces — so the real content changes stand out.
Is my text uploaded?
No. The comparison runs entirely in your browser with JavaScript, so your text never leaves your device. It is safe for private drafts, contracts and confidential documents.
Normalising text first gives cleaner diffs: run both versions through our case converter if case differences are masking real changes, and use our syllable counter if you’re comparing poetry or lyrics line by line.
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