Win the openbefore you write the email.
The subject line is the only part of your email most people ever see. This tester grades it on the levers that move open rates, length, word count, spam risk, personalization, emotion, curiosity, gives you a score and a fix list, and shows you exactly how it'll look in Gmail, Outlook, and on a phone.
Your subject line
Use a merge tag like {{first_name}} to test a personalized version.
The read
Subject score
A+
Characters
46
Words
8
Spam risk
Low
Inbox preview
iPhone Mail (portrait)
The 4-second problem killing your l…cut
Gmail (desktop)
The 4-second problem killing your landing page
Outlook (desktop)
The 4-second problem killing your landing page
Apple Mail (desktop)
The 4-second problem killing your landing page
Signal by signal
46 characters
Ideal — high-open subjects cluster around 30–50 characters.
8 words
Scannable length.
Clean of spam triggers
Nothing here that screams promotions folder.
No personalization
Where it fits, a first-name or company token raises open rates.
Carries a hook
Emotional or power words give the reader a reason to open.
Has a number
Specifics and open loops both pull the open.
Your move
A great subject opens the email. A great email books the call.
Your subject scored 90/100 (A+) — 46 characters.
I write the subject, the email, and the sequence behind it, built around how aware your reader is and what you actually want them to do. Bring me a campaign that's getting opened but not converting and I'll show you, free, where it's leaking.
Plain English
No open, no email. It all rides on this line.
Roughly a third of people decide whether to open an email based on the subject line alone. Everything you crafted inside, the offer, the story, the call to action, is gated behind one short string of text. Which makes the subject line, dollar for word, the highest leverage copy you'll write all week.
A strong subject does a few things at once: it's short enough to survive truncation (most clients cut around 35 to 60 characters), it sounds human rather than promotional, it earns curiosity or promises a clear benefit, and it dodges the trigger words that route mail to spam. Get those right and you're not manipulating anyone, you're respecting a crowded inbox.
This tester scores all of it instantly: ideal length, word count, spam signals, personalization tokens, emotional and power words, and curiosity levers like numbers and questions. Then it renders an inbox preview so you can see where each client truncates, because the most common subject line mistake is burying the hook past the cutoff.
The formula
Open rate ≈ relevance × curiosity × deliverability ÷ friction
"Your 4 second problem" (20 chars) is short, specific, curiosity driven, and clean, it scores high and shows in full everywhere. "DON'T MISS our HUGE limited time SALE!!! 50% off everything" is long, shouting, spam heavy, and truncated mid pitch, it scores low and likely never gets seen.
What actually lifts opens
The levers that correlate with higher open rates across large email datasets. Use them as defaults, then test against your own list, your audience is the only benchmark that fully counts:
| Lever | What works |
|---|---|
| Length | 28 to 50 characters / 3 to 9 words |
| Tone | Human & conversational, not promotional |
| Personalization | First name token with a fallback |
| Curiosity | A number, a question, or an open loop |
| Spam triggers | Zero stacked promo words / ALL CAPS |
| Emoji | At most one, test it |
Source: Mailchimp / Campaign Monitor subject line benchmarks · 2025
Your subject scored low. Here's why.
Over ~50 characters.
Mobile shows about 35 characters, desktop around 60. Front load the hook so the part that earns the open survives the cut. Check the preview below.
Spam trigger words.
Salesy words and stacked punctuation route you to Promotions or spam. Rewrite to sound like one person emailing another, with at most one promo signal.
No curiosity or benefit.
A subject that states the obvious gives no reason to open. Add an open loop (a number, a question) or a concrete benefit the reader wants.
No personalization.
Where it fits, a first name or company token lifts opens, just set a sensible fallback so it never renders blank or broken.
Flat, generic wording.
'Newsletter #42' earns nothing. One emotional or power word, or a specific detail, turns a label into a reason to click.
How to write subjects that get opened
01Front load the hook
Put the most compelling word in the first 35 characters. Assume everything after it gets cut on mobile, because it often does.
02Sound like a human
The subjects that win look like a note from a friend, not a banner ad. Lowercase, conversational, specific. Promotional polish kills opens.
03Open a curiosity gap
Promise an answer you don't fully give. A number, a question, or an unexpected claim creates the itch to open, just make sure the email pays it off.
04Use one emotion or benefit
Give the reader a single clear reason: a feeling, a benefit, or a tension. Two competing ideas dilute both.
05A/B test relentlessly
Subject lines are the easiest thing in marketing to test. Run two per send, keep the winner, and compound the learning over time.
06Write the preheader too
The preview text right after the subject is free real estate. Extend the hook there, don't waste it on 'view in browser.'
The vocabulary
- Open rate
- The share of delivered emails that get opened. The metric the subject line exists to move (noting Apple's Mail Privacy now inflates it).
- Preheader
- The preview text shown after the subject in the inbox. A second hook most senders waste.
- Curiosity gap
- A subject that promises information it withholds, creating the urge to open. Must be paid off inside.
- Personalization token
- A merge tag like a first name or company that tailors the subject to the recipient and lifts opens.
- Truncation
- Where an email client cuts off a long subject, about 35 chars on mobile, 60 on desktop.
Subject line questions, straight answers
Aim for about 28 to 50 characters, or roughly 3 to 9 words. That's short enough to show in full on mobile, where most email is opened, and long enough to say something specific. If you go longer, front load the hook so the important part survives truncation.
Keep going
A calculator tells you what. A call tells you what to do about it.
Send me the account behind these numbers. I'll tell you straight where the money's leaking and what I'd fix first — free, and you keep it whether you hire me or not.