Troubleshooting Custom CSS, Javascript, and HTML in Klaviyo

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If you are importing a custom HTML template, or building your own custom coded template, there are a few things to consider.


We only recommend using custom HTML for technically savvy marketers, or for anyone who has access to a developer. While our product does support custom HTML, our support team is unable to help you build out your custom templates beyond offering the general guidance covered in this documentation.

To maintain the security of your data, Klaviyo's support team is not able to open your HTML files. 

Custom HTML and CSS Elements

If you're creating a custom HTML template, you cannot use product feeds within your email.

Certain HTML and CSS elements used to make emails interactive are not currently supported. For example, if you are looking to make your email interactive in Gmail by using certain CSS attribute selectors, you may see your template trigger an error in Klaviyo.

Klaviyo does not currently support certain operators (like ~) in email templates. This may limit the extent to which certain custom HTML and CSS can be used. If your template contains HTML or CSS that isn't fully supported, you will not be able to generate a preview of your email and will see the following error:


What issues should I look for if my custom HTML isn't rendering properly?

If you're finding that your custom HTML email does not look correct, here's a few common places to check for problems.

  1. Single Quotes in Font

    Wherever you're adding a font-family in the CSS, look for single quotes or unnecessary quotes. Remove all quotes when adding in your font.

    Problem Fixed
    font-family:'Helvetica Neue', Helvetica, Arial font-family:Helvetica Neue, Helvetica, Arial
  2. Media Queries 

    If media queries are not in the standard format, it will not render properly. Follow the standard format for all media queries.

    Standard Media Query Format
    @media only screen and (max-width: 460px)
  3.  Unnecessary Center Tags 

    If you have multiple HTML <center> tags throughout your email template, your email may not render properly in Gmail. To fix this issue, remove all unnecessary <center> tags. Only one <center> tag is needed at the top of the email template near the <body> tag. All additional <center> tags are superfluous.

Klaviyo Does Not Support JavaScript Emails

Most email clients (Gmail, Hotmail, Yahoo, etc.) view JavaScript in emails as a security threat. This is because scripts can hide malicious content. As a result, these major email clients block scripts in emails entirely. Given the inherent security threat associated with JavaScipt in emails and the lack of support for such scripts by most major email clients, any added scripts will automatically be removed.

Klaviyo Does Not Support Embedded Forms or Videos

Klaviyo does not support embedded forms, widgets, or videos in templates. This is because our testing shows that these types of features do not reliably render across all major email clients. Similar to JavaScript snippets, most email clients view these elements as a security threat and strip them out of emails altogether.

Learn more

If you're interested in learning workarounds for this, check out this article on Adding a Video or GIF to an Email.
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