Subject line tester.
Score your cold email subject lines, see how they look in the inbox, and compare versions before you hit send.
Subject lines · compare up to 5
- 100
- 39
- 98
iPhone Mail
Alex Morgan9:41
quick question
Saw Northwind just opened a Berlin office. Congrats on the new team.
Gmail app
Alex Morgan9:41 AM
quick question
Saw Northwind just opened a Berlin office. Congrats on the new team.
Gmail desktop
Alex Morganquick question – Saw Northwind just opened a Berlin office. Congrats on the new team.9:41 AM
Previews are approximate: exact cut-off depends on screen size and font.
Strong
2 words · 14 characters
Best of 3
Word count
2 words: short and personal, like a colleague would write.
Fits on mobile
14 characters: shows in full on phones.
Spam trigger words
No common spam words.
No hype or false urgency
Calm and specific.
Doesn't sound like a pitch
Doesn't give away a pitch.
Punctuation
Clean punctuation.
Natural capitalisation
Reads like a normal message.
Honest (no fake Re:/Fwd:)
No fake reply prefix.
No emoji
No emoji.
Placeholders
No unfilled tokens.
Subject lines that get opened.
In cold email, the best subject line looks like it came from a person, not a brand.
quick question
Quick Question About Your Sales Process!!
Short, lowercase and calm reads like a colleague, not a campaign.
northwind's berlin team
Unlock Growth With Our AI Platform
About their world, not your product.
idea for {{company}}
RE: our conversation
Personal and honest. Fake replies destroy trust the moment they open.
Great subject lines need a clean inbox to land in.
Deliveryman sets up your domains, mailboxes and warmup so your emails reach the inbox, where people can actually open them.
Frequently Asked Questions
What makes a good cold email subject line?
Short (1–5 words), lowercase or sentence case, specific to the recipient, and free of hype. The goal is to look like a message from a real person, because that's what gets opened.
How long should a subject line be?
Under about 33 characters so it shows in full on phones, where most email is opened. iPhone Mail shows around 38 characters; the Gmail app shows a little less.
Should I personalize the subject line?
Yes, when it's natural: a company name or a relevant detail works well. Make sure every lead has a value for the token, or set a fallback, so nobody gets “{{company}}” in their inbox.
Do spam words in the subject line really matter?
They matter more in the subject than anywhere else. Modern filters weigh many signals, but words like “free”, “guarantee” and “act now” combined with caps or exclamation marks are a classic spam pattern.
How do I use the compare mode?
Add up to 5 versions. Each gets a score, the best one is marked with a trophy, and you can click any version to see its inbox preview and checks. Then A/B test your top two with real sends.
Is this a replacement for A/B testing?
No. It catches the mistakes that sink open rates before you send. Real A/B tests with your audience are still the best way to pick a winner.