HTML Viewer
Paste HTML, CSS and JavaScript and see it rendered live in a secure sandbox. Nothing is uploaded.
Why Use DiffMergy’s HTML Viewer?
DiffMergy’s HTML Viewer renders your HTML, CSS and JavaScript live in a secure sandboxed iframe. Paste markup and instantly see the result, then keep editing and re-render without setting up a local server or build step.
The preview runs in an isolated sandbox so untrusted snippets cannot reach the rest of the page, and script execution is off by default. Everything happens locally in your browser — no upload, no account, no external requests.
100% Private — No Server Upload
All processing happens entirely in your browser using modern browser APIs. Your sensitive source code, credentials, and files never leave your device — no servers, no databases, no tracking, no sign-up required.
Fast & Reliable
Built with vanilla TypeScript and a lightweight custom engine, DiffMergy delivers sub-millisecond processing with zero network latency. The entire toolkit works on any modern browser across all operating systems, with no installation or setup needed.
Frequently Asked Questions
How do I preview HTML online?
Paste your HTML, CSS and JavaScript into the editor on the left. The sandboxed preview on the right renders it live as you type. Tick 'Allow scripts' to run JavaScript inside the sandbox.
Is the HTML preview safe and private?
Yes. The preview runs in a sandboxed iframe with scripts disabled by default, and everything happens locally in your browser. Your code is never uploaded.