StackBlitz
stackblitz.com
Runs npm install and a Node dev server inside the browser itself
Free tierOn device
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codepen.io
Write HTML, CSS and JavaScript in a tab and watch it render live.
The front-end scratchpad: three panes, instant preview, preprocessors for Sass, TypeScript and friends, and one-click package includes. It is also a searchable archive of other people's CSS experiments, which is why it doubles as a reference when you are trying to remember how someone did a particular effect. Pens are public on the free plan — private pens, asset hosting and collaboration mode all require Pro.
AltFTool does this too
If you would rather not leave the site, HTML Editor covers the same job here — free, no account, and it runs in your browser.
Open HTML EditorQuestions
A genuinely usable free tier with paid plans for volume or team features. Everything saved on the free plan is public and searchable; private pens need a paid account.
Yes. CodePen 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.
Everything saved on the free plan is public and searchable; private pens need a paid account.
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