Is your subject line
worth opening?
Get a brutally honest score on your email subject line's clarity, urgency, and curiosity — plus 3 rewrites. Free in 30 seconds.
Newsletter, cold outreach, promo, drip — any subject line you want scored.
30 seconds · No signup · Always free
What you get
A real score — not “looks good!”
Most feedback on your subject line is polite or generic. Ours scores it against 4 specific criteria with evidence, then writes 3 alternatives that fix what's broken.
Clarity Score
Is it immediately clear what the email is about?
Urgency Score
Does it create a reason to open now?
Curiosity Score
Does it create an information gap that demands a click?
3 Rewrites
Better subject lines written for your specific email.
Ready to find out if your subject line is actually working? Score my subject line →
Most subject lines fail the same way
They describe the email instead of selling the open. "March Newsletter" tells me what it is. It doesn't give me a reason to open it. The best subject lines make the reader think "I need to know what's inside" before they even click.
The fix is almost always the same: replace the label with the payoff. "March Newsletter" becomes "The pricing mistake that cost us $12K."
Why shorter almost always wins
Mobile shows ~40 characters. Desktop shows ~60. If your subject line gets cut off at the most important part, it's not working. Front-load the interesting part. Save the details for the preview text.
The test is simple: read just the first 5 words of your subject line. If those 5 words aren't compelling on their own, rewrite it.
Your subject line is one piece. Boost shows the full picture.
The subject line score shows what lands in the inbox. A Boost Brief shows your full competitive landscape — who you're up against, where they're weak, and where you should attack. Free, no signup.
Get my full Boost — $29One-time payment. No subscription.
Curiosity without clickbait
The best subject lines open a loop that the email closes. "You won't believe what happened!" is clickbait — it promises vaguely and usually disappoints. "We tested 3 pricing pages. One converted 4x better." is curiosity — it's specific, honest, and the email delivers.
The difference is specificity. Clickbait is vague. Curiosity is specific enough to be believable but incomplete enough to demand the click.
Subject lines that actually get opens
The highest-performing subject lines share three traits:
- 1.They create urgency ("ends Friday" not "check this out")
- 2.They're specific ("3 mistakes killing your cold emails" not "improve your emails")
- 3.They feel personal ("quick question about your pricing page" not "important update")
You don't need all three. But the more you stack, the harder it is to skip your email.
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Questions you might have.
Yes. No credit card, no trial, no sales calls. You get a real analysis with scores and rewrite suggestions. We built this so you can see what Boost does before you ever spend a dollar.
Any email subject line you're about to send or have sent — newsletters, cold outreach, product announcements, drip sequences, promotional emails. If it shows up in someone's inbox preview, paste it in.
ChatGPT will tell you your subject line is 'great!' and suggest minor tweaks. We score it against specific criteria (clarity, urgency, curiosity, relevance) with evidence. Most subject lines score 30-55. We won't sugarcoat it.
The rewrites get dramatically better. Without context, we can only fix structure. With context (what the email is about, who's receiving it), we write subject lines that are specific to your audience and your message.
We don't share your data, sell your email, or send spam. We use your subject line to generate the analysis and your email to send results. That's it.