Question 1

How do I compare two versions of an HTML email?

Accepted Answer

The RenderOps Campaign Diff Comparator shows a side-by-side or inline unified diff of two HTML email versions, highlighting added lines in green and removed lines in red. It works at the source code level so you can spot every change from modified copy to adjusted inline styles.

Question 2

Why is email code diffing important?

Accepted Answer

When multiple people work on email templates, accidental changes to table widths, inline styles, or CTA button colors can break rendering across clients. A code diff viewer lets you review exactly what changed between versions before approving and sending, preventing costly rendering errors.

Question 3

Can I compare email HTML from two different ESPs?

Accepted Answer

Yes — paste any two HTML blocks and the Diff Comparator will show the exact differences. This is useful for comparing Klaviyo-exported HTML vs. Mailchimp-exported HTML of the same design, spotting where each ESP injects its own code into your template.

Question 4

Does the Diff Comparator work offline?

Accepted Answer

Yes — the diff algorithm runs entirely in your browser with no server round trips. Paste your two HTML versions and get an instant comparison, even without an internet connection once the page has loaded.

HTML Diff Viewer Online