Diff Checker
Compare two text blocks and highlight the differences.
By Syed Mubashir Ali · Last updated
Comparing drafts without losing your place
The side-by-side view is best when both texts are long and you want to keep your bearings: original on the left, revised on the right, changes highlighted in both. The inline view stacks everything into one column (removals struck through, additions highlighted) which reads better on a phone and works well when one side is much shorter than the other.
Whichever view you use, the jump arrows are the real workflow. A 40-page contract might have eleven changes; the arrows walk you through all eleven in order, and you never have to scroll-hunt. Tick 'Ignore spaces' before you start if the document was reformatted. It hides the hundreds of fake 'changes' that are really just re-indentation.
Word or character: which precision to use
The right level depends on what you're hunting. Pick wrong and you'll either miss the change or drown in highlights.
Word mode (the default, right for prose)
Use it for documents, articles, emails, contracts. A rewritten sentence shows as a handful of swapped words, which is exactly how an editor thinks about the change. This is the mode you want 90% of the time.
Character mode (for typos and code)
Use it when the difference is tiny: a corrected typo, one changed digit in an account number, a renamed variable. In word mode these show as a whole highlighted word; character mode pinpoints the exact letters. Essential for code and data.
Ignore toggles (for reformatted files)
Not a granularity, but the fix for the most annoying diff problem: someone ran the file through a formatter, so every line 'changed'. 'Ignore spaces' hides whitespace-only differences; 'Ignore case' hides capitalisation-only ones. Apply them first, and the real edits stand out.
How to Use Diff Checker
- 1Paste the original text on the left and the changed text on the right, or open a file into either side: the file is read locally, never uploaded.
- 2The differences appear as you type: removed words are highlighted in the original, added words in the modified text.
- 3Use the arrows to jump from one change to the next, or switch to the inline view to see removals and additions together in one column.
- 4Choose Characters for letter-level changes such as typos, and tick Ignore case or Ignore spaces to hide changes you don't care about.
- 5Tick 'Code font' when you're comparing source files or data: monospaced type keeps indented blocks aligned so the structure reads properly.
- 6When you're done, clear either side with the reset button. Nothing was uploaded, so closing the tab wipes it too: handy for contracts and anything confidential.
Frequently Asked Questions
Does it show which words changed, or whole lines?
Individual words. It first finds which lines or paragraphs changed, then compares those word by word, so a one-word edit in a long paragraph highlights just that word. Switch to Characters to see single-letter changes.
Will my text keep its formatting?
Yes. Both sides are shown exactly as you pasted them (the same paragraphs, line breaks, spaces and tabs) with only the changed words highlighted. Long lines wrap instead of scrolling sideways.
What algorithm is used?
The Myers diff algorithm, the same one Git uses, via the open-source jsdiff library. Everything runs in your browser; your text is never uploaded.
Can I compare code files?
Yes. Open or paste any text file (code, JSON, CSV, Markdown) and tick Code font for a monospaced view.
Can I compare files without copy-pasting?
Yes, use the open-file buttons on either side. The browser reads the file on your device and the contents never leave it, so even a 2 MB server log is safe to compare here.
What's the difference between Word and Character mode?
Word mode highlights whole changed words, which is what you want for prose: a rewritten sentence shows as swapped words, not a mess of letters. Character mode highlights individual letters, which is better for spotting typos, a changed digit in a long number, or a renamed variable in code.
There's a wall of highlighted text, where do I start?
Use the jump arrows. They step through each change in order, so you review one edit at a time instead of scanning a sea of highlights. For long documents, ticking 'Ignore spaces & blank lines' first often removes most of the noise.
About Diff Checker
Someone sends you 'final_v2.docx' after you already reviewed 'final.docx', and swears only the date changed. Or a client approves copy, then the published page reads differently and nobody knows who edited what. The Diff Checker settles it in seconds: paste both versions and every changed word lights up, in context, with both texts otherwise exactly as you pasted them.
It's a daily tool for more jobs than you'd expect. Lawyers compare contract redlines without waiting for Word's track-changes to render. Editors check that a writer's 'small tweaks' didn't rewrite the intro. Students see what their proofreader actually changed. Developers diff config files between staging and production. The common thread: two versions, one truth, no guessing.
Underneath it's the Myers diff algorithm (the same one Git uses) running through the jsdiff library entirely in your browser. That last part matters more than it sounds: because nothing is uploaded, you can compare confidential documents and unreleased copy without sending them anywhere. Close the tab and it's gone.