Score your subject line against nine checks, and see exactly where a phone cuts it off. Runs in your browser, gives you the answer straight away.
A good winback subject line would be a bad review request. Pick the type and the scoring changes with it.
The narrowest common view, and where the line gets cut first.
Subject and preheader share one line here, so a long subject eats the preheader. Scroll the row sideways to see all of it.
A phone cuts it around 35 characters, so "time only" is only read on desktop. Check the first 35 characters still make the point on their own.
More words means more of them get cut. Try 3 to 7, and put the noun the reader cares about first.
IT'S and BACK are shouted. Emphasis works once. Twice, and it is the shouting the reader notices, not the words.
Fine if the news is genuinely good news. If the sentence works without it, it is doing the enthusiasm for you.
An ecommerce email is allowed to say limited. What costs you is stacking three of them, or putting one in capitals.
Nothing to fix. One emoji can lift a promotional send, but it has to add something the words do not.
Fine. Naming the product they looked at usually beats naming the person, and it never renders as an empty gap.
Two deadlines in one line cancel each other out. The reader stops reading it as information and starts reading it as pressure.
This is what the second line is for: the detail that would have made the subject too long.
Fifty lines you can send, or take apart. Click any one to load it into the tester above with the right campaign type already selected.
Nobody opens a newsletter for a deadline. They open it for the sender and for one specific thing worth reading. Say the thing.
They already chose the item. Name it and get out of the way. Discounting in the subject line teaches people to abandon carts on purpose.
Browse Abandonment Email Subject Lines
The easiest subject line to overthink, because the reader already asked for this update. Name the product and get out of the way.
Back In Stock Email Subject Lines
First impression, and the only email where the reader knows nothing yet. Be warm, be short, and say what happens next.
You are asking a favour, so it has to read like a person asking. Promotional styling here (caps, emoji, exclamation marks) makes a sincere question look like an ad.
They left for a reason. Acknowledge the gap, give them one reason to look again, and do not pretend the last six months did not happen.
The only urgency a shopper trusts is a number. "Only 4 left" is a fact. "Hurry" is a feeling, and they have read it a thousand times.
The number is the message. A price drop email with no price in the subject line is asking the reader to open it to find out whether it was worth opening.
They have already paid. This one is service, not selling. Selling in the subject line spends the goodwill.
Post-Purchase Email Subject Lines
Everyone is running one. The offer and the end date do more work than any adjective you can put in front of them.
This is why the tester scores a welcome email differently from a restock alert. Across 22.66 million emails our merchants sent, open rates differed substantially by email type. Campaign context is part of judging a subject line, not a detail you can factor out of it.
| Email type | Sends | Open rate |
|---|---|---|
| Back in stock | 428,895 | 63.1% |
| Review requests | 444,915 | 49.1% |
| Workflow automation | 2.44M | 39.4% |
| Loyalty | 275,643 | 33.3% |
| Broadcast campaigns | 19.32M | 31.5% |
| All email | 22.66M | 32.8% |
| Flow | Sends | Open rate |
|---|---|---|
| Post-purchase | 79,387 | 50.7% |
| Browse abandonment | 38,301 | 49.1% |
| Checkout abandonment | 124,587 | 37.2% |
| Welcome | 17,427 | 27.9% |
These four sit inside the 2.44 million workflow sends in the other table, so the two do not add up. One more flow is left out completely: its delivery rate in this snapshot was low enough that we will not quote its open rate until we know why.
Aggregate across all OnVoard merchants, from a snapshot taken before July 2026, and it includes outliers. It shows how email types performed, not what wording did on its own. Intent, timing, sender recognition, deliverability and the offer all move these numbers, and a type with intent already behind it starts ahead. Treat it as the shape of the thing, not as a forecast for your store.
Short enough to survive a phone. About 35 characters is a conservative working target, because that is roughly where the narrowest common inbox views start to truncate.
| Where it is read | Roughly what shows |
|---|---|
| iPhone Mail, held upright | 35 to 40 characters |
| Gmail app on a phone | 35 to 45 characters |
| Outlook on the desktop | around 60 characters |
| Gmail on the web | around 70, then the preheader takes the rest of the line |
| Apple Mail on a Mac | 80 or more, on a wide window |
Ranges, not guarantees. Every one of these moves with the window width, the font size and whether the reader has larger text switched on, which is why the previews in the tester truncate with real CSS instead of cutting at a number. The practical rule survives all of it: put the thing that matters first, and treat everything after the first 35 characters as a bonus.
These are the exact lists the spam check above runs on. Worth saying plainly: modern filters weigh your sending reputation, your authentication and how people engaged with your last few sends far more than your wording. None of these words will get you blocked on their own. What they do is tell a shopper, in the half second they spend scanning, that this is an advert.
act now · buy now · order now · apply now · call now · click here · click below · risk free · risk-free · 100% free · free money · cash bonus · no cost · no obligation · you have won · you are a winner · congratulations you · once in a lifetime · this is not spam · make money · earn extra · double your · miracle · lowest price ever · unbeatable · best price ever · satisfaction guaranteed · dear friend · incredible deal · $$$
free · discount · offer · deal · save · promo · clearance · bonus · exclusive · limited · instant · massive · huge · amazing · incredible · blowout · mega
An ecommerce email is allowed to say sale, free shipping and 20% off. The tester only marks these down past two in one line, or when one is in capitals or followed by an exclamation mark. A tool that penalised a store for writing "20% off" would be wrong about the job.
last chance · final hours · final call · ending soon · ends soon · ends tonight · act fast · hurry · don't miss · do not miss · today only · now or never · while supplies last · while stocks last · limited time · urgent · expires soon · expiring soon · running out · almost gone · nearly gone · last day · going fast · only hours left · don't wait · do not wait
None of these is banned. On a sale that ends Sunday or a product with four left, urgency is information. On a welcome or a review request, nothing is running out, and borrowed urgency teaches the reader that your deadlines are decorative. The tester scores them differently for exactly that reason, and it wants a number or a date alongside: "only 4 left" is checkable, "hurry" is not.
These are two different jobs and they run in that order. A score of 92 is not a prediction of your open rate, and no tester can give you one.
It reads the line the way a shopper scanning an inbox would, and it catches what is wrong before anybody sees it: a line cut in half on a phone, two deadlines that cancel each other out, a merge tag with no fallback. It knows nothing about your list, your products or your sender reputation.
Use it to remove the obvious weaknesses and to get from one draft to two strong candidates.
It answers the only question that finally matters: which line did your subscribers open. That answer belongs to your audience, and it is why a subject line scoring lower here can beat one scoring higher.
Send the two finalists to a slice of the list, give it enough recipients to mean something, and let the result decide. On a small list the gap will often be noise, and picking the clearer line is the better use of your time.
Nine checks, each worth a fixed number of points that add up to 100: length and mobile truncation, word count, capitalisation, punctuation, spam language, emoji, personalisation, urgency, and the preheader. Every check shows what it scored, so you can disagree with one and still use the rest.
Because a check in the red caps the verdict. Nine scores added together let one real problem hide behind eight fine ones, and a shouted line with two fake deadlines can still total in the seventies. The number never moves, only the words next to it.
Because the same sentence is good or bad depending on what the email is. "Last chance" is fair on a sale that ends Sunday and dishonest on a welcome email, where nothing is running out. Urgency, emoji tolerance and the right length all move with the type.
No, and no tool can promise that. Filters weigh your sending reputation, authentication and how people have engaged with your last few sends far more than your wording. The spam check here is about how the line reads to a shopper who has seen ten thousand of them.
Roughly 35 characters on a phone and 60 on the desktop, which is the conservative end of what mail clients show. Exact widths change with the device, the font size and whether the reader has larger text switched on, so the previews truncate with real CSS rather than cutting the string at a count.
No. The scoring runs in your browser. Nothing is posted anywhere, nothing is stored, and there is no email field between you and the result.
Sending the email is the other half. See how OnVoard sends it. More free tools: see every free tool, including the pricing calculator and the markup calculator.
OnVoard sends the restock alert, the cart reminder and the review request when they are worth opening, from the same place you send your campaigns.