What is an email HTML checker?

It reads the HTML source of an email and reports the parts that email clients handle differently from browsers, such as unsupported CSS, missing alt text, oversized layouts and markup that exceeds the size at which Gmail truncates a message.

Is my email HTML uploaded anywhere?

No. The markup is parsed in your browser with DOMParser and never leaves your machine. That matters because email templates often contain merge tags, customer names in test data and unsubscribe tokens.

Why does flexbox not work in email?

Outlook for Windows renders mail with the Microsoft Word HTML engine, which it has used since 2007. Word never implemented flexbox or grid, so those declarations are ignored and children fall back to stacked block elements.

What is the 102KB Gmail limit?

Gmail stops rendering a message once the HTML passes roughly 102KB and hides the remainder behind a "View entire message" link. Content after the cut is invisible by default, and tracking pixels placed at the bottom stop firing.

Why should email be 600px wide?

Outlook’s default reading pane is narrower than 600px on a typical laptop, and it crops rather than scales. Six hundred pixels has been the safe content width for two decades because it fits every common reading pane.

Do I really need inline styles?

For anything structural, yes. Outlook.com, Yahoo Mail and some mobile clients strip or rewrite blocks, so an email styled only in the head can arrive as unstyled text. Use for media queries and dark mode on top of inline base styles.

Why add role="presentation" to tables?

Screen readers announce a table as tabular data, reading out row and column counts before the content. A layout table marked role="presentation" is skipped, so the reader hears the message rather than the scaffolding.

Will this tool preview my email?

No. It checks the markup rather than rendering it. Static analysis catches structural problems a screenshot cannot show, such as an unclosed tag or a stylesheet link no client will fetch. Send a real test message for the visual pass.

Can I check a template from Mailchimp or Klaviyo?

Yes. Export or view the campaign source and paste it in. Note that merge tags expand at send time, so the live message is usually larger than the template you are checking.

Does clean HTML improve deliverability?

It helps. Filters score unbalanced markup, hidden text and scripts, all of which appear in obfuscated spam. Clean markup removes those signals, though authentication, list hygiene and sending reputation matter far more.

Free Email HTML Checker

Paste your email HTML and see what breaks before you send. The checker flags CSS that Outlook drops, styling that webmail strips, images with no alt text, layouts wider than the reading pane and markup past the size at which Gmail clips a message. Everything runs in your browser.

Free, no signup Nothing uploaded Outlook, Gmail and webmail rules

Add your email HTML

Paste the full source, or choose an .html file.

Markup clean? Next is the send

Stop hand patching email HTML.

Grigora Email builds campaigns on templates that already use table layout, inline styles and 600px containers, so the problems this checker looks for never get written. Your list, your site and your newsletter live in one place.

Start free Explore Email

How to check email HTML

Four steps from source to a send you can trust.

Paste the HTML

Copy the full source of the email, starting at the DOCTYPE, or upload the .html file.

Run the check

The markup is parsed in your browser. Nothing is sent to a server.

Fix the errors

Errors break rendering in a major client. Warnings degrade it for part of your list.

Re-check and send a test

Run it again, then send yourself a real test in Outlook and Gmail.

How to check email HTML, step by step

Real screenshots of the tool, taken while checking a template with known Outlook problems.

1
Paste the email HTML
Any exported template works. The checks run in the browser, so a campaign you have not sent yet stays private.
2
Load the example
The example includes the mistakes that break Outlook most often, so you can see what each finding looks like before testing your own file.
3
Work through the errors first
Every finding says why it matters and which client breaks, from an external stylesheet Gmail strips to a flex row Outlook stacks into a column.

When to run the check

Six moments worth spending thirty seconds on.

Before sending a campaign

A rendering bug found after the send cannot be fixed. Check the final HTML, not the draft.

After hand editing a template

One deleted closing tag in a table cell can collapse everything below it in Outlook.

When Outlook looks wrong

Find the flexbox, the positioning or the max-width that Word quietly dropped.

When Gmail clips the message

Measure the HTML against the 102KB limit and see how far over you are.

Reviewing a bought template

Marketplace templates vary. Check the alt text and table roles before you rely on them.

Writing transactional email

Receipts and password resets get read on phones under time pressure. They have to render.

Getting the HTML out of your platform

Where the source lives, by platform.

Grigora Email

Open the campaign and choose the code view.
Copy the full HTML.
Paste it here before you schedule the send.

Mailchimp

Open the campaign, then Preview.
Choose "View code" and copy the source.
Remember merge tags expand at send time.

Klaviyo

Open the template and switch to the HTML editor.
Select all and copy.
Check before cloning the template for a flow.

Hand coded or MJML

Build the template as usual.
Take the compiled HTML, not the source.
Upload the .html file directly.

Grigora vs. other ways to check

Side by side.

Capability	Grigora	Preview services	Send a test	Browser preview
Runs without upload	Yes, in your browser	Uploads your HTML	Sends a real message	Nothing to check
Explains why a rule exists	Yes, on every finding	Screenshots only	No	No
Catches unclosed tags	Yes	No	No	No
Measures the 102KB limit	Yes	Sometimes	No	No
Signup required	No	Yes, paid	Account needed	No

Common errors and how to fix them

Eight problems that show up in real campaigns.

Columns stack in Outlook

Cause: The row uses display: flex.

Fix: Rebuild the row as a table with one td per column and fixed pixel widths.

Message is cut off in Gmail

Cause: HTML exceeds 102KB.

Fix: Strip comments, shorten repeated inline styles, and remove any base64 images.

Everything arrives unstyled

Cause: Styling lives only in a <style> block.

Fix: Inline the base styles. Keep the block for media queries and dark mode only.

Blank boxes where images were

Cause: Images are blocked and have no alt attribute.

Fix: Give every meaningful image alt text, and alt="" for spacers.

Screen reader reads a grid

Cause: Layout tables have no role="presentation".

Fix: Add role="presentation" to every table that is not real tabular data.

Horizontal scroll in the inbox

Cause: A table or image is wider than 600px.

Fix: Cap the content table at 600px and set image widths in pixels.

Fallback font looks wrong

Cause: A web font is loaded with @import.

Fix: Write a full font stack. Design against the fallback, not the web font.

Footer escapes the container

Cause: A td or table is never closed.

Fix: Close every tag. Browsers repair this silently, Outlook does not.

Email numbers worth memorising

The four constraints behind most rendering complaints.

102 KB

Point at which Gmail clips a message and hides the rest

600 px

Widest content that fits an Outlook reading pane without cropping

2007

Year Outlook switched to the Word engine, which is why flexbox still fails

Bytes of your email sent to a server by this tool

Frequently asked questions

Ten answers about email HTML.

Related free tools

Other utilities that pair with the Email HTML Checker.

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