CodePen
codepen.io
Write HTML, CSS and JavaScript in a tab and watch it render live
Free tierClassic
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diffchecker.com
Shows exactly what changed between two blocks of text, side by side.
Paste two versions and every insertion and deletion is highlighted, updating live as you edit either side. Beyond plain text it will diff PDFs, images, Excel sheets and whole folders, which is the part people forget it can do and the reason it survives on non-developers' bookmark bars. The text diff runs in the page, but the file-based comparisons upload your documents, and the free tier caps how large those can be.
AltFTool does this too
If you would rather not leave the site, Diff Checker covers the same job here — free, no account, and it runs in your browser.
Open Diff CheckerQuestions
A genuinely usable free tier with paid plans for volume or team features. File comparisons upload your documents and hit a size cap on the free tier; only the text diff stays local.
Yes. Diffchecker sends your input to its own servers to process it. That is fine for public material; for anything containing personal data, use one of the on-device tools instead.
File comparisons upload your documents and hit a size cap on the free tier; only the text diff stays local.
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