Generate subject lines for an email. Optimize for an accurate expectation of the message, not artificial urgency or curiosity. The recipient should understand enough to decide whether opening is worthwhile. Audience and relationship to sender: [AUDIENCE] Email purpose and single desired action: [PURPOSE AND ASK] Core message or offer: [EMAIL CONTENT] Tone and brand constraints: [TONE CONSTRAINTS]
Relevant timing or context: [TIMING CONTEXT]
Produce a table with 18 options in four groups: direct and descriptive (5), benefit-led (5), timely or contextual (4), and personal/reply-style only if honestly justified (4). Keep most options 30–55 characters; note any that exceed 60. Include a preheader of 35–80 characters for the best six options.
For each option, label the intended audience segment, the promise it makes, and the risk it avoids. Write a short recommendation naming the best three for this exact email and explain the trade-off between clarity, intrigue, and deliverability. Do not use “Re:” or “Fwd:” unless this is a genuine reply or forward. Do not imply a deadline, relationship, result, or personalization I have not provided. Avoid all caps, repeated punctuation, deceptive “you,” and words likely to create spammy pressure.
Before answering, verify that every subject accurately matches the email’s content and that each option has a distinct angle. Ask up to three clarifying questions only if a required input is missing.Fill in
| Placeholder | What to enter | Example |
|---|---|---|
| [AUDIENCE] | Describe who will receive the email, their relationship to the sender, and what they care about. | Existing trial users of a project-management app who have not invited teammates; they know the product but may be busy. |
| [PURPOSE AND ASK] | State the email’s purpose and the one action you want recipients to take. | Encourage them to invite one teammate before their 14-day trial ends. |
| [EMAIL CONTENT] | Paste or summarize the actual message, offer, event, or update in the email. | The email explains shared project views, mentions a short setup guide, and offers a live onboarding session on Wednesday. |
| [TONE CONSTRAINTS] | Describe the tone and any words, claims, or styles the sender should avoid. | Helpful and practical; avoid hype, guilt, and claims that the product will transform their team. |
| [TIMING CONTEXT] | Enter a real date, deadline, trigger, or seasonal context only if it appears in the email. | Recipients have between three and five days left in their trial; do not state a specific date. |
How to use
- Paste the actual email or a faithful outline; a subject line cannot truthfully promise more than the body delivers.
- Choose a group that fits the recipient’s awareness, then test the top two or three options with comparable audience segments.
- Check that a time-sensitive line reflects a real deadline visible in the email.
- Follow up with: “Create six plainer alternatives to option 4 for recipients who have never opened an email from us.”
Variations
Cold outreach lines
Use this for a first email to someone who does not know you.
Write 15 subject lines for a cold email to [RECIPIENT TYPE] about [REASON FOR OUTREACH]. My credible relevance is [RELEVANCE], and my requested action is [ASK]. Group them into direct, shared-context, and problem-specific options. Keep each under 50 characters, avoid false familiarity and clickbait, and pair the best five with a 50-character preheader. Explain which three are least likely to feel mass-sent. Do not invent a mutual connection, result, or recipient pain point. Ask up to three questions only if required inputs are missing.
Newsletter subject lines
Use this for a recurring editorial email with several articles.
Create 16 newsletter subject lines from this issue: [ISSUE CONTENT]. The subscribers are [AUDIENCE], and the editorial voice is [VOICE]. Offer four literal table-of-contents lines, four lead-story lines, four tension or insight lines, and four curiosity lines that remain accurate. Add preheaders for the top eight. Rank the best four by fit with the issue’s main value, and flag any line that promises more than the contents deliver. Keep most lines under 55 characters; ask up to three questions only if inputs are missing.
Event reminder lines
Use this for a registration or attendance reminder with a real date.
Generate 12 subject lines for an event email. Event: [EVENT]. Audience: [AUDIENCE]. The action is [ACTION], and the true deadline or event time is [DATE AND TIME]. Split options into registration reminder, practical logistics, and value-focused. Add a preheader to each. Use urgency only when the stated timing supports it, include the time zone when helpful, and do not imply seats are limited unless I confirm that. Self-check accuracy against the event details; ask up to three questions only if needed.
Tips
- A subject line should make the body feel like a kept promise; draft the body’s central sentence first.
- Use one true reason to open, such as a concrete update or a deadline, instead of stacking vague benefits.
- Reply-style subjects can damage trust when they mimic an existing conversation, so reserve them for actual threads.
- When testing, change one angle at a time; otherwise an open-rate difference is hard to interpret.
FAQ
What length should an email subject line be?
Thirty to fifty-five characters is a useful target, but clarity matters more than an arbitrary limit. Mobile displays will truncate many longer lines.
Are questions good subject lines?
Only when the recipient can answer them from a genuine concern addressed by the email. Avoid generic questions designed only to create curiosity.
Can AI predict the highest open rate?
No. It can create reasoned options, but a controlled test with your actual audience is the evidence.