Write HTML, CSS and JavaScript in three panes and see the result at once, with a console, errors pointed out by line and a link to share. The preview runs in an isolated environment with no access to this site's data.
The editor has three panes, HTML, CSS and JavaScript, and a preview that refreshes when you stop typing (or when you click Run). The preview is an iframe with sandbox="allow-scripts" and srcdoc content, without allow-same-origin. In practice that gives your code an opaque origin: it runs real JavaScript, but it cannot read cookies, localStorage or the site's DOM, submit forms, open popups, navigate the main window, or open alert, confirm or prompt dialogs, which become console lines. The code never runs in the jkit.tools origin. Inside, a small script injected ahead of yours forwards console.log, info, warn, error and debug, uncaught errors, rejected promises and images or scripts that fail to load, and the site only accepts messages from that iframe's window and the current run. A JavaScript error appears over the preview with the line from the JavaScript pane and marks the line in the editor. The share link stores the code in the URL fragment, after the #, which the browser never sends to any server, compressed with deflate when the browser offers CompressionStream. Code opened from a link does not run until you click Run, and the page reminds you not to type passwords into the preview. You can download everything as a single .html file, paste a complete page (starting with doctype or html) into the HTML pane, and load libraries from a CDN or call APIs with fetch. Honest limits: there is no autocomplete, multi-file support or npm modules, the Tab key moves focus instead of indenting (so the keyboard stays accessible), and an infinite loop can freeze the tab; in that case the preview is flagged as unresponsive, and after a freeze auto-run stays paused.
Paste the code into your HTML and the tool shows up on your page, without J-Kit's navigation and ads. It still runs in the browser of whoever visits your site.
<iframe
src="https://jkit.tools/embed/en-US/html-editor-online"
width="100%"
height="600"
style="border:0"
loading="lazy"
title="Online HTML Editor"
></iframe>
<p style="font-size:12px;margin:6px 0 0">Tool by <a href="https://jkit.tools/en/tools/html-editor-online">J-Kit</a></p>Using it in a paper, class or post? Copy the link or a ready-made reference. The access date is today's.
<a href="https://jkit.tools/en/tools/html-editor-online">Online HTML Editor</a>
These references help contextualize formulas, standards, APIs and limitations used on this page. They do not replace professional validation when a result has legal, financial, medical or operational impact.
Write in the three panes and the preview updates at once. There is no account, server or file: the browser builds a page with your HTML in the body, your CSS in a style tag and your JavaScript at the end of the body, and runs it all in an isolated iframe. The console shows whatever the code prints.
The preview runs isolated: your code cannot see cookies, storage or this site's page.
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