Live, side-by-side previews
Compare up to four clients, or one client in light and dark. Set the viewport anywhere from 240 to 1,600 px and watch your breakpoints respond.
VS Code extension for Adobe Marketo Engage
Preview every inbox before you send.
Leadlens shows your email in 21 email clients as you type, flags what will break, and understands Marketo Email Editor 2.0 variables, modules and tokens.
Free · Runs locally · No account
21 client simulations, light and dark
- Gmail
- Gmail Android
- Gmail iOS
- Outlook 365
- Outlook (New)
- Outlook Classic
- Outlook iOS
- Outlook Android
- Outlook for Mac
- Apple Mail
- Apple Mail iOS
- Yahoo Mail
- Yahoo Mail Android
- Yahoo Mail iOS
- Samsung Mail
- Thunderbird
- HEY Mail
- Proton Mail
- AOL Mail
- Fastmail
- Superhuman
Everything you check before a send, inside your editor.
No uploading, no switching tabs and no waiting for a render farm. Edit the HTML and see the result.
Built for Email Editor 2.0
Templates, complete emails and components. Variables, module values and token fallbacks resolve locally, and runtime-only tokens stay clearly marked.
Linting where you write
Compatibility, accessibility, links, images, size and dark-mode contrast, underlined at the exact line, with explanations on hover and one-click fixes.
Marketo Email Editor 2.0
Made for Marketo templates, not generic HTML.
Leadlens reads your template the way Marketo does, so you see real content instead of ${variable} placeholders, and no false alarms about valid tokens.
- Every variable type, with module-scoped preview values
- Token fallbacks applied; runtime-only tokens clearly marked
- Preview a custom component inside a real template region
- Outline, hovers, Go to Definition and completions
- A read-only view of the prepared HTML. Your source never changes
<!-- leadlens-disable-next-line border-radius -- VML covers Outlook -->
Linting
Know what breaks, where, and for whom.
Every finding points at the exact characters responsible, even through Marketo substitutions and linked stylesheets, and names the clients it affects.
Fix the mechanical ones in one click, tune severities for your team, and silence deliberate choices with a comment that records why.
Private by default.
Runs on your machine
No telemetry, no account, and no network requests of its own. Leadlens never connects to Marketo.
Tracking pixels stay quiet
Remote images are blocked until you allow them, so previewing never tells a sender their email was opened.
Sandboxed previews
Code in an email can't run, and only images inside your workspace can load. Your source is never changed.
Install in three steps.
- 01DownloadGet
leadlens.vsixfrom the latest release. - 02InstallIn VS Code: Extensions → ⋯ → Install from VSIX. Or run
code --install-extension leadlens.vsix. - 03PreviewOpen an email and run Leadlens: Open Preview to the Side.
Requires VS Code 1.90 or later. Compatibility data comes from the open-source Emailens engine and updates with each new build. To update, install the newest download over the top.
Questions
Anything else is probably in the documentation.
Is Leadlens free?
Yes. Leadlens is free and open source, under the MIT licence. There's no account, trial or paid tier.
Does it connect to my Marketo instance?
No. Leadlens works on HTML files in your editor and never connects to Marketo or any other platform. Open a template or email you've saved locally, and it recognises the Email Editor 2.0 syntax.
How accurate are the previews?
They simulate each client from its documented behaviour: which HTML and CSS it supports, how Outlook handles conditional comments and VML, and how dark mode recolours the email. They aren't screenshots from the real apps, so for important sends a final check in the inboxes that matter most is still worthwhile.
Does my email content leave my computer?
No. Leadlens has no telemetry and makes no network requests of its own. Remote images in the preview stay blocked until you allow them; once allowed, they load from wherever the email hosts them.
What do I need to run it?
Visual Studio Code 1.90 or later. MJML files also need the mjml package installed in your project.
Does it only work with Marketo emails?
No. Any HTML email gets previews and linting, and MJML is supported too. The Marketo features switch on when Leadlens detects Email Editor 2.0 syntax.
How do I update?
Download the latest build and install it over the top; it replaces the installed version. Each build includes the newest compatibility data from the Emailens engine.
See your next send in every inbox.
Free, local and ready in a minute.