How do you test merge fields in automation?

You've built your automation, written your welcome email with "Hi {{first_name}}!", and you're about to hit launch. But what happens when {{first_name}} is blank? Or when someone's name is "José" or "Mary-Kate" or a string of 47 characters? That's what merge field testing is for.

Here's how to do it properly, not just click preview once and call it done.

Build dedicated test profiles

Don't test with your own email address. Create at least three test contacts in your ESP: one with every field fully populated, one with key fields deliberately empty, and one with edge-case values (very long name, special characters, accented letters, numeric values in text fields). Klaviyo, ActiveCampaign, and Mailchimp all let you create test contacts you can rotate through during preview.

Test with complete data first

Send to your fully-populated test profile. Confirm every merge field renders in the right place, with the right capitalisation, and in every location it appears (subject line, preview text, body, CTA). It's easy to fix a field in the body but forget you also used it in the subject.

Then test with missing data

This is where things break. Send to your empty-field profile and check that your fallback values actually show up. If you wrote "Hi {{first_name | fallback: 'there'}}" in Klaviyo or "Hi *|FNAME|*" in Mailchimp, does the email read "Hi there" or does it read "Hi "? That blank space is what you're testing for.

Test edge cases before they reach real subscribers

Add a contact with a long value ("Bartholomew-Fitzgerald"), one with special characters ("O'Brien", "André"), and one where a field contains a number stored as text. Run each through the sequence and check that nothing breaks the layout or the sentence structure around it.

Check merge fields inside dynamic content blocks

And if you're using merge fields inside conditional content ("show this block if {{city}} is London"), test the merge field and the condition together. A field can render correctly in a plain paragraph but fail silently inside a dynamic block.

Send actual test emails, not just preview mode

Preview mode in most ESPs shows you a simulation. The real rendering happens when the email is actually sent. Use your ESP's "send test" feature and route each test profile through your actual test seed address. Mailtrap is useful here if you want to catch test sends without cluttering a real inbox.

Now once you've confirmed every scenario renders cleanly, you're ready. If you're still stuck on a specific merge tag syntax or a fallback that won't cooperate, our SOS hotline is free and we're happy to take a look.