Email subject line generator with preview text for each line
Your email can be great and still go unread if the subject line looks like every other promo in the inbox. With this prompt your todo.is agent reads your email, writes twenty subject lines in different styles with matching preview text, and flags which ones fit on a phone screen.
The prompt
- Write 20 subject lines for my email. Here is the email: [PASTE OR ATTACH YOUR EMAIL]. It goes to [WHO RECEIVES IT] from [SENDER NAME]. The goal is [GOAL, E.G. OPENS, CLICKS, REPLIES]. Write 4 lines each in 5 styles: clear benefit, curiosity, question, personal or casual, and urgency (only if there is a real deadline: [DEADLINE OR "NONE"]). Keep each under 45 characters so it fits on a phone, and add a preview text of 40 to 90 characters that adds new information instead of repeating the subject. No all caps, no fake "Re:" or "Fwd:", no spam-trigger phrases like "100% free". Mark the 2 you would A/B test and say why. Put everything in a table.
What to change
- [PASTE OR ATTACH YOUR EMAIL]: The email body, or attach it as a file or screenshot.
- [WHO RECEIVES IT]: e.g. "newsletter subscribers who bought once" or "B2B leads from a webinar".
- [SENDER NAME]: How it shows in the inbox, e.g. "Nina from Fieldnote".
- [GOAL, E.G. OPENS, CLICKS, REPLIES]: What matters most for this email.
- [DEADLINE OR "NONE"]: e.g. "sale ends Sunday midnight". Never invent urgency.
Example result
- Email: Fieldnote notebooks restock, sale ends Sunday
- | Style | Subject line | Preview text |
- |---|---|---|
- | Benefit | The dot-grid notebook is back | Restocked in all 6 colors, plus 15% off until Sunday |
- | Benefit | Your favorite notebook, 15% off | The A5 dot-grid sold out in March. It is back today. |
- | Benefit | Restocked: the lay-flat notebook | 120 gsm paper, no ink bleed, and free shipping over $40 |
- | Benefit | New colors in the Fieldnote A5 | Sage and rust joined the lineup. Here is a first look. |
- | Curiosity | We made 3,000 more. That is it. | Why this restock might be the last one this year |
- | Curiosity | The notebook people kept asking for | 412 of you joined the waitlist. Here is what changed. |
- | Curiosity | Something changed in the paper | Same notebook, slightly heavier pages. You will feel it. |
- | Curiosity | This took us 7 months | The story behind the new sage cover, and a discount |
- | Question | Ready for a new notebook? | The dot-grid is back with 15% off until Sunday |
- | Question | Which color are you picking? | Sage, rust, navy, black, sand or grey, all restocked |
- | Question | Did you miss it last time? | It sold out in 9 days. Here is your early access. |
- | Question | Paper or screen for planning? | Why 3 of our readers switched back to paper this year |
- | Personal | Nina here, quick news | The notebook you asked about is finally back |
- | Personal | I saved you one | Early access for subscribers before the public restock |
- | Personal | A small thank you | 15% off the restock, just for people on this list |
- | Personal | It is back (finally) | Thank you for waiting. Here is your code. |
- | Urgency | 15% off ends Sunday | The restock discount closes at midnight on Sunday |
- | Urgency | Last day: 15% off notebooks | Sale ends tonight at midnight. Free shipping over $40. |
- | Urgency | 48 hours left on the restock deal | After Sunday the price goes back to normal |
- | Urgency | Closing tonight | Your 15% notebook code expires at midnight |
- What to A/B test
- • "The dot-grid notebook is back" vs "We made 3,000 more. That is it."
- • One is clear, one is curious. Testing two different styles tells you more about your list than testing two similar lines.
- Notes
- • Send the Sunday urgency lines only as a reminder to people who did not open the first email.
- • Use only real numbers. Replace 412 and 3,000 with your actual waitlist and stock.
How to do it with todo.is
- Copy the prompt and paste or attach your email where it says [PASTE OR ATTACH YOUR EMAIL].
- Fill in the audience, sender name, goal and deadline, then send it in todo.is or by WhatsApp.
- Your agent returns a table of 20 subject lines with preview text and two picks for testing.
- Set up the test in your email tool. Tell your agent which line won so it learns what your list likes.
Tips for a better result
- Preview text is a second subject line. Use it to add a detail, not to repeat the subject or say "View in browser".
- Shorter usually reads better on phones. Aim for the key words in the first 30 to 40 characters.
- Only use urgency when it is real. Fake deadlines train subscribers to ignore you.
- Test styles against each other, and keep a list of past winners. Your agent can remember them for next time.
email subject line generator: FAQ
- How long should an email subject line be? Around 30 to 50 characters is a common guideline, because mobile inboxes cut off longer lines. Put the important words first.
- What is preview text in an email? Preview text, or preheader, is the short line that shows after or under the subject in most inboxes. If you leave it empty, the inbox shows the first words of your email instead.
- What words trigger spam filters? Spam filters look at many signals, not just words, but heavy use of phrases like "100% free", "act now", all caps and lots of exclamation marks can hurt. Sender reputation matters more.
- Can todo.is send the email campaign? No, use your email marketing tool for campaigns. Your agent writes and tests copy and can save single emails as Gmail drafts if Google is connected.
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