What Online HTML Viewer does
Online HTML Viewer takes the source you enter and, when you select Render preview, places it in an iframe document with UTF-8 encoding, a restrictive content security policy, and an empty sandbox permission list. The preview can display ordinary HTML and inline styling without giving the fragment access to the surrounding page.
This is a static inspection surface, not a full browser testing environment. JavaScript applications, form flows, external stylesheets, remote media, and navigation are intentionally unavailable. The source is not repaired or certified as valid, so use a dedicated validator and security review before putting untrusted markup into a production context.
How to use Online HTML Viewer
- Paste or type the HTML fragment into the source field.
- Select Render preview to create a new restricted iframe view.
- Inspect the visible structure, text flow, and inline styling.
- Return to the source to revise it, then render again when you want to refresh the preview.
Important details
Rendering is explicit
The preview changes when you select Render preview rather than on every keystroke. This makes it easier to compare the current view with a source edit in progress.
The sandbox isolates active behavior
Scripts, forms, pop-ups, top navigation, same-origin access, and external network loads are blocked. The fragment cannot opt itself into additional iframe permissions.
Source correctness is not evaluated
Browsers recover from many malformed tags, so a visible result does not prove the markup is valid, accessible, semantic, or consistent across browsers.
Practical uses
- Preview a small static fragment supplied in documentation or a support ticket.
- Inspect how basic HTML elements nest before using a validator.
- Demonstrate markup structure without allowing active page behavior.
Privacy and limitations
The entered source is rendered locally and is not uploaded by this tool. The preview blocks external network requests, so remote assets in the fragment are not contacted from the iframe.
JavaScript, form submission, navigation, pop-ups, external assets, and same-origin behavior are unavailable. The viewer does not validate or sanitize source for later use and cannot reproduce a production site's full runtime.