Will my email subject line get read or skipped?
Last updated
Every check runs as you type. Nothing is sent anywhere.
Up to 90 characters. Merge tags are fine; write them as your email platform does.
Optional, but the check on it fails until it is here.
Up to 120 characters.
Paste a subject line and seven checks run as you type.
- Your subject lineNeeded
- Your preview textRecommended
The seven things this checklist reads
A subject line tester reads an email subject and its preview text against a checklist before you send, so The linen shirt is back in stock, followed by a preview naming the colours and sizes, clears every check, while HUGE SALE followed by three exclamation marks and Act now fails on capitals, punctuation and a scam-sounding phrase.
The checklist, its length bands and its phrase list are Nudgesmart’s own. They are not a published standard, not any filter’s rules and not drawn from anyone’s send results.
Two lines decide whether an email is opened: the subject and the preview text beside or under it. Every check below reads one or both of them, and each one fails for a reason a person scanning an inbox would notice too.
- Subject length
- Checked against our own band of 15 to 50 characters. A phone shows the start of a subject and cuts the rest, so the band is about keeping the point visible, not about a magic number. Anything past 70 is flagged harder.
- Preview text
- The grey line after the subject. Our band is 35 to 110 characters, and it fails if it simply repeats the subject. Left empty, the inbox fills it with whatever the email starts with.
- Merge tags
- Placeholders such as a first-name tag that your email platform fills in per reader. Using one is optional. The check only fails when a tag is opened and never closed, because a broken tag goes out as raw text with the braces showing.
- Specific
- The line promises one concrete thing: a number, a named offer such as free shipping, a product that is back, or a time such as tonight. Vague lines such as Some news give the reader nothing to decide on.
- Shouting
- Two or more words in capitals, more than one exclamation mark, repeated punctuation or a run of emoji. Short names such as VIP or SPF are allowed.
- Scam-sounding phrases
- A list we wrote for this page of phrases that make a real email read like junk: act now, risk free, you have won, click here and similar. No filter publishes its rules, so this is a reading check, not a filter simulation.
- Fake reply
- A subject that opens with RE: or FW: on an email nobody replied to. It fails every time, because it is a trick and readers recognise it.
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Seven subject lines put through the checklist
Illustrative subjects and previews, not real sends and not a ranking of what gets opened. Each row is scored by the same function the tester above runs.
| Scenario | Subject | Preview text | Checks | First fix |
|---|---|---|---|---|
| The welcome email nobody reads | Welcome! | — | 4 of 7Needs a rewrite | Too short to say anything. Name the thing inside: the offer, the product or the reason to open. |
| A sale shouted | HUGE SALE!!! Act now | Everything must go this weekend only | 4 of 7Needs a rewrite | Give the reader one concrete thing: an amount, a product name, what is new, or when something ends. A reader decides whether to open from what the line promises. |
| Restock with a clear reason to open | The linen shirt is back in stock | All five colours, in sizes XS to XXL, while this batch lasts. | 7 of 7Clears every check | Nothing to fix on the checklist. |
| Personalised, but the tag is broken | {{ first_name, your 15% code is inside | Use it on anything in the store before Sunday at midnight. | 6 of 7Workable, with fixes | Close the tag exactly as your email platform writes it. A broken tag sends as raw text, with the braces showing, to everyone on the list. |
| Fake reply to look personal | RE: your order | Our autumn edit is here, with free shipping over the weekend. | 4 of 7Needs a rewrite | Too short to say anything. Name the thing inside: the offer, the product or the reason to open. |
| Deadline, offer and a preview that adds detail | Free shipping ends tonight | Order by midnight and it ships free, no minimum spend. | 7 of 7Clears every check | Nothing to fix on the checklist. |
| Everything crammed into the subject | Our biggest ever end of season sale is finally here with savings across every single categ | Our biggest ever end of season sale is finally here | 5 of 7Workable, with fixes | Well past the 50 characters a phone tends to show. Put the point in the first few words and move the rest into the preview text. |
What no subject line checklist can see
Clearing every check does not mean people will open it
The checklist reads the words. Whether your readers care about the offer, trust the sender name and expect to hear from you are bigger factors, and none of them can be read from a subject line.
Delivery is decided before the subject is read
Whether an email reaches the inbox depends mostly on the sending domain, its authentication records and how readers have treated your past emails. A clean subject cannot rescue a domain with a poor record, and a single spam-sounding word rarely sinks a good one.
Inboxes cut lines in different places
Where a subject is truncated depends on the app, the screen and the font size, and it is set by width on screen rather than by a character count. The preview on this page is a rough guide, not a copy of any particular inbox.
The spam-phrase list is ours
It is a short list written for this page, not a copy of any filter. Words not on it can still count against an email, and some words on it are harmless in context.
Email subject line questions
How long should an email subject line be?
Short enough that the point survives on a phone. This checklist passes 15 to 50 characters, which is our own guidance. Lines longer than that are fine as long as the words that matter come first, because the end is what gets cut.
What is preview text and do I need it?
It is the short line shown after the subject in most inboxes. You do not have to write it, but if you do not, the inbox uses the first text in the email, which is often a view-in-browser link. Use it for the detail the subject had no room for.
Do capital letters and exclamation marks hurt an email?
They make it read like a hard sell, and some filters weigh them alongside other signals. One exclamation mark is fine. A subject in capitals with three of them fails this checklist, and it tends to fail with readers too.
Does this predict my open rate?
No. It is a checklist of things a subject line can be read for, not a model of any inbox and not built from anyone else’s results. The only open rate that means anything for your list is the one your own email platform reports.
Should I use the first name in the subject line?
It is optional, and this checklist does not reward it. What it does check is that the tag is written correctly, because a broken tag sends the raw placeholder to everyone on the list.
Can I share the result?
Yes. The copy link reproduces your subject and preview in the tester, so whoever opens it sees the same checks. Subjects are capped at 90 characters and previews at 120; a line packed with emoji can be too long to fit in a link, and the tester then says so instead of making one.
The inbox is the second step. The signup is the first.
Nudgesmart builds the popup that collects the address, and reports email captures and the email capture rate for each campaign.
