Is this a test in real email clients?

No. It checks your source for known problems and shows a browser preview. Email clients render HTML differently, so send a test to real mailboxes too.

No. The check and preview run in your browser, and the preview is sandboxed so scripts and forms cannot run.

Why is 102 KB mentioned?

Gmail clips messages larger than about 102 KB, hiding the rest behind a link. Anything important at the bottom, such as links, can be lost.

HTML email checker and preview

Updated 2026-11-03

Email HTML is not web HTML. Clients strip scripts, ignore modern CSS and block images. Paste your source to catch the usual problems before you send.

Paste your email's HTML

Everything runs in your browser. Your HTML is not sent to Inboxili or stored.

What it checks

| Area | Examples | |---|---| | Size | Over about 102 KB, where Gmail clips | | Unsupported markup | Scripts, forms, video, iframes, external stylesheets | | Unsupported CSS | Flexbox, grid, positioning, background images | | Images | Missing alt text, missing widths, http:// sources | | Links | Relative URLs, empty links, javascript: URLs | | Structure | Missing doctype, viewport and title, very wide layouts, div-only layouts | | Content | Unfilled {{merge tags}} |

About the preview

The preview is an iframe with no permissions and a content security policy that blocks scripts and non-https resources. That makes it safe to paste untrusted HTML. It shows how a modern browser draws your markup, at desktop width or a 375px phone width. It does not reproduce Outlook for Windows, which uses a different rendering engine, or Gmail's CSS stripping.

A reliable email layout

Build layout with table elements and inline styles.
Keep the main container at 600px or less.
Set a width and alt text on every image, and a background colour behind any text on an image.
Use https:// for every link and image, and full URLs everywhere.
Add a plain-text version alongside the HTML.

The email template builder generates this structure for you.

Before you send

Send a test to a few mailbox providers, run the spam-risk check in the campaign editor, and confirm your domain's records with the email DNS checker.

Frequently asked questions

Is this a test in real email clients?: No. It checks your source for known problems and shows a browser preview. Email clients render HTML differently, so send a test to real mailboxes too.
Is my HTML uploaded?: No. The check and preview run in your browser, and the preview is sandboxed so scripts and forms cannot run.
Why is 102 KB mentioned?: Gmail clips messages larger than about 102 KB, hiding the rest behind a link. Anything important at the bottom, such as links, can be lost.

Build and send emails with Inboxili

Create a workspace, verify a domain, and make your first API call.

Build and send emails with Inboxili Read the API docs