An HTML email builder is a browser-based tool that lets you create, edit, and preview HTML email templates before sending them to your subscribers or customers. Instead of relying on a single browser view, you can use an email preview tool to check how your email looks across different layouts, devices, and themes.
ToolsViewer's HTML Email Builder works as a free online email tester for checking email templates directly in your browser. You can paste your HTML, import .html, .htm, .eml, or .mime files, and preview the rendered email without installing additional software.
The HTML email tester includes client-style previews for desktop and mobile layouts, along with light and dark themes. This makes it easier to perform an email rendering test before using your template in an email service provider.
You can also format HTML, inline CSS, minify your email source, test merge-tag values, and run checks for HTML, links, headers, source code, and other common email issues. For dark mode email testing, simply switch the preview to dark mode and review how your colors, backgrounds, text, and other elements appear.
The previews are browser-based simulations rather than native Gmail or Outlook rendering engines, so they should be used for development and QA rather than as a replacement for testing in actual email clients.
Step 1: Add Your Email HTML
Paste your email code into the editor or import an .html, .htm, .eml, or .mime file. You can also start with one of the available templates.
Step 2: Preview Your Email
Choose a client-style preview and select desktop or mobile form factors. You can also switch between light and dark themes to see how the email changes.
Step 3: Clean and Personalize Your Template
Use Format HTML, Inline CSS, or Minify to prepare your email code. If your template contains merge tags such as {{variable}}, use the Payload option to add sample JSON values and preview personalized content.
Step 4: Run Email Checks
Use Check Email to review the HTML, source, text, headers, QA report, HTML compatibility, and links before downloading or sending a test.
Step 5: Download or Send a Test
Download your finished email as email-template.html, or send a test through your own Mailpit-compatible HTTPS endpoint.
.htm, .eml, and .mime importsTest HTML Emails Before Sending
Use the email tester free workflow to review your email template before adding it to your email marketing or transactional email platform.
Check Email Rendering
Run an email rendering test to see how your HTML email appears across different device sizes and preview themes.
Test Dark Mode Emails
Use dark mode email testing to review text, backgrounds, buttons, images, and other elements in a dark interface.
Preview Transactional Emails
Check receipts, password reset emails, account notifications, onboarding messages, and other transactional templates before deployment.
Test Saved Email Files
Import an .eml file and inspect its rendered content, source, headers, and available checks.
Test Personalized Emails
Add sample merge-tag values through Payload JSON to see how dynamic content will appear in your email template.
Check Email Links and HTML
Run HTML Check and Link Check to catch common issues before handing your email template over to your email service provider.
The HTML Email Builder supports common email development formats and testing options:
.html files.htm files.eml files.mime filesemail-template.htmlAuthoring in MJML instead? Use MJML Email Builder. For screenshot or PDF captures of HTML, see HTML to PNG, HTML to JPG, or HTML to PDF. Setup help: Mailpit + ngrok guide.