mailcannon.
HTML Email Previewer

Preview & Test Your HTML Email Before Sending

Paste HTML email code, preview it on desktop and mobile, inspect the generated HTML, and catch common rendering issues — all safely in your browser.

Email HTML
Paste a full HTML document or just an HTML fragment. Your code never leaves your browser.
Rendered in a sandboxed iframe. Scripts and event handlers are stripped. Nothing is uploaded.
Live Preview
Approximate visual environment — real email clients can render differently.
Preview mode:
Width:
Background:
Zoom:100%
From: sender@example.com
To: recipient@example.com
Subject: (no subject)

Preview modes provide an approximate visual environment. Actual rendering can vary between email clients and versions.

Email HTML Analysis
Statistics and warnings based on the actual HTML in your editor.
Paste HTML above to see size, structure, images and link statistics.
Link Analysis
Every link found in your HTML, with protocol and anchor text.
Links will appear here after you paste HTML.
Image Analysis
Every image in your HTML with size, protocol and alt text status.
Images will appear here after you paste HTML.
Email Accessibility Checks
Advisory checks only — this is not a WCAG certification.
Accessibility checks will appear here after you paste HTML.
Is this tool private?
Yes. Everything runs locally in your browser. Your HTML is never uploaded to our servers, never stored, and we do not make network requests to the images or links in your email.

What Is an HTML Email Previewer?

An HTML email previewer is a browser-based tool that renders your email HTML the way an inbox would — inside an isolated, sandboxed preview — so you can see how your design looks before it reaches a single recipient. Instead of sending test emails back and forth, you paste your HTML once and instantly switch between desktop and mobile, test common email widths, inspect the code and catch rendering problems.

Why Should You Preview an HTML Email?

HTML email is fragile. A layout that looks perfect in your browser can break in Outlook, clip on a phone or load images that are too large. Previewing lets you catch broken layouts, missing images, broken links, horizontal overflow and accessibility problems before you send — when fixing is cheap and no subscriber has seen a broken message.

Why Does HTML Email Look Different Across Email Clients?

  • Different rendering engines. Gmail uses a modern engine, Apple Mail uses WebKit, and Outlook on Windows uses Word's HTML engine — three very different worlds.
  • Different CSS support. What one client supports (flexbox, media queries, background images) another silently ignores.
  • Different widths. Desktop panes, mobile viewports and zoom settings all change how wide your email actually renders.
  • Version and device drift. Even the same client changes rendering between versions and platforms. There is no single 'standard' inbox.

How to Preview an HTML Email

  1. Paste your HTML. Full documents and fragments both work — no need to include <html> or <body>.
  2. Add an optional subject. It appears in the simulated email header.
  3. Select desktop or mobile. Switch to check responsiveness and watch for horizontal overflow.
  4. Inspect the preview. Use preview modes, widths and zoom to approximate different inbox environments.
  5. Review warnings. The analysis panels flag scripts, forms, HTTP images, missing alt text and more.
  6. Fix problems. Edit the HTML and watch the preview update.
  7. Copy or download the final HTML. Use it directly in your ESP.
  8. Send a test email. Real clients still deserve a real test — this tool is a fast pre-flight check, not a replacement.

HTML Email Best Practices

Table-based layouts
Tables with inline styles are still the most reliable structure across all email clients.
Inline CSS
Avoid external stylesheets. Most clients ignore <style> or <link> tags; inline styles always work.
HTTPS images
Host images over HTTPS and give every image meaningful alt text for accessibility.
Responsive layouts
Test at 600px desktop and ~380px mobile. Use fluid tables and media queries carefully.
Simple fonts
Stick to web-safe fonts like Arial or Georgia. External fonts are unreliable in email.
Accessible links
Use descriptive link text, not 'click here', and make sure your email is readable without images.
How is the preview kept safe?
Pasted HTML renders in a sandboxed iframe with scripts, event handlers and javascript: URLs stripped.
Check your subject
Want a subject score and rewrite ideas?
Subject Line Tester
Generate email HTML
Start from scratch with AI.
AI HTML Email Generator

Frequently asked questions

Test for spam risk
Email Spam Checker
Craft the perfect preview
Preheader Generator
Rewrite your copy
AI Email Rewriter

Security & Privacy

The preview runs entirely in your browser. Your HTML is rendered inside a sandboxed iframe with sandbox="allow-same-origin", scripts, event handlers, forms, iframes and javascript: URLs are stripped before rendering, and the preview cannot navigate or access the MailCannon application. Your HTML is never uploaded to our servers and it is never stored. The tool also never downloads your images or visits your links — all analysis is based on the source HTML alone.