EmailSubjectScore Pro vs Zurb TestSubject

These tools do completely different things. Zurb TestSubject is about preview — how does your subject visually look in someone’s inbox on iPhone Mail, Gmail app, Outlook mobile. Does it get cut off? Does the preheader flow right?

EmailSubjectScore Pro is about quality — is this subject going to hit spam? Is it clear? Does it create urgency? Can the AI write a better version?

Honestly, you could use both. They don’t overlap at all.

Side-by-side

	EmailSubjectScore Pro	Zurb TestSubject
Primary purpose	Score + rewrite subject quality	Preview subject rendering across mobile clients
Where it lives	Inside your Gmail compose window	zurb.com/playground/testsubject (web)
AI rewrite suggestions	✅	❌
Spam / clarity / urgency scoring	✅	❌
Cross-client visual preview	❌	✅ (iPhone Mail, Gmail iOS/Android, Outlook mobile)
Preheader / sender preview	❌	✅
Requires signup	❌	❌
Cost	Free (Pro tier planned)	Free

Using them together (actually a good combo)

Here’s the flow that makes sense:

1. Type your subject in Gmail. EmailSubjectScore Pro scores it live. If it’s weak, click “Suggest rewrite” and get a better version.
2. Once you’re happy with the content, paste it into Zurb TestSubject to check it won’t get truncated on mobile.

Two problems. Two tools. Neither replaces the other.

But if you only pick one…

If your problem is “my emails aren’t getting opened” — that’s a quality problem. EmailSubjectScore Pro.

If your problem is “my subject looks fine but gets cut off on iPhone” — that’s a rendering problem. Zurb TestSubject.

Most people reading this page have the first problem, not the second. Just a guess.

Try it free

Install EmailSubjectScore Pro from the Chrome Web Store →

No signup. 50 scores + rewrites/month.

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Full disclosure: this comparison is by the team behind EmailSubjectScore Pro. Zurb TestSubject is a beloved free classic in the email marketing community — genuinely useful and complementary to our tool.