Free tool
Subject line checker
Type a subject line to see how it looks in a phone inbox, with checks for length, promotional words and merge fields.
Check your subject line
The preview fills merge fields with sample values (first name Dana, company Northfield Roasters).
- LengthAt most 70 characters, and best under 45: a phone shows about 35 to 45 before it cuts the line.
- Word countTwo to eight words. One word says nothing; a sentence is an email body.
- No promotional wordsWords like free, urgent, deal or guaranteed belong to adverts. So do worn openers like quick question.
- No hype wordsSeamless, unlock, powerful: the same list our emails are checked against.
- No shoutingNo words in capitals and no exclamation marks.
- No pricesMoney in the subject line reads as a sales offer before they have read a word.
- No fake reply or forwardStarting with Re: or Fwd: when there was no earlier email is deceptive, and the law in several countries says so.
- Merge fieldsA merge field like {{first_name}} is fine if every recipient has a value. An empty one sends a broken subject.
Checked as you type, in your browser. Nothing is sent anywhere and nothing is stored.
How to use it
- Type your subject line. Add the first line of your email as preview text, because the inbox shows it right under the subject.
- Look at the phone preview: that is all most people see before they decide to open or delete.
- Fix any rule marked Fix. The score updates as you type.
What good looks like
A good cold subject line looks like one a colleague would write: short, lower-key, and about them. It names the thing you noticed or the thing you can help with, in four to six words.
- Good:
Standing orders for Northfield cafes,Your Saturday clinic waiting list. - Weak:
Quick question(says nothing),Re: our call(there was no call),Boost your sales 10x!(an advert).
The preview text matters as much: if your email starts with a specific observation, the inbox shows it for free.
Questions
How long should a cold email subject line be?
Under 45 characters is safest: a phone inbox shows roughly 35 to 45 characters before cutting the line. Our own limit for any subject is 70.
Do spam words in a subject line send email to spam?
Not on their own. Filters judge mostly on the sender's reputation and authentication. But promotional words make people delete or report the email, and those reports are what hurts delivery.
Should I personalise the subject line?
Only with something true and specific, like their company or a service they run. A first name alone is common enough that it no longer stands out, and an empty merge field is worse than none.
More free tools: Cold email checker · DMARC checker · Cold email legal checker · Reply classifier · Gmail warm-up calculator. All of them run in your browser; nothing you type is sent to us.
See what it would write for you
Paste your website. Honest Intros learns what you sell and shows who it would write to, and what it would say.
Free to start. Nothing is sent until you approve it.