Subject lines are the only thing 95% of subscribers see. A good subject prompt names the audience, the email type, and the promise — then generates 5-7 variants so you can A/B without the agonizing.
Who this is for
Newsletter writers, lifecycle marketers, founders writing onboarding sequences, indie devs who send a monthly update.
When not to use these prompts
Don’t use clickbait subjects on emails that don’t deliver. Don’t use them for transactional emails (the body matters more there).
Prompt anatomy / structure formula
Every subject-line prompt should carry six elements:
- Audience: one specific reader.
- Goal: one outcome — read / click / agree / share.
- Voice: 2-3 anchor adjectives, optional sample line.
- Constraints: word count, banned phrases, must-include facts.
- Format: paragraph, bulleted, headed, table.
- Examples: 1-2 tone samples — best lever for matching voice.
Best for
- Newsletter subjects
- Onboarding sequence subjects
- Re-engagement subjects
- Sales outreach subjects
- Subject A/B test brief
12 copy-ready prompt templates
1. 7 variants from a brief
Email type: `{type}`. Audience: `{audience}`. Email promise: `{promise}`. Write 7 subject-line variants ≤ 60 chars each, ranging: (a) curiosity, (b) benefit-led, (c) specific number, (d) controversial, (e) name-drop, (f) question, (g) plain. Avoid emojis unless stated.Variables to swap: type — newsletter / onboarding / re-engage / sales, audience, promise
2. Subject + preview pair
For this subject `{subject}`, write 3 preview-text pairings ≤ 90 chars. Each preview should EXTEND the subject, not repeat it. Test by reading both lines aloud — they should sound like a sentence cliffhanger.Variables to swap: subject
3. Curiosity without clickbait
Write 5 curiosity-driven subjects that pay off in the email body. Forbidden: "You won't believe…", numbers without specificity, "this one trick". Each subject must be 100% true based on the email content.4. Benefit-led subjects
Audience cares about: `{outcome}`. Write 5 benefit-led subjects ≤ 50 chars. Lead with verb. No "how to" if a tighter version works ("Cut churn by 12%" beats "How to cut churn").Variables to swap: outcome
5. Re-engagement subjects
Write 5 re-engagement subjects for a subscriber inactive 60+ days. Tones: (a) self-aware ("We get it…"), (b) plain ("Still want X?"), (c) value-led ("New feature you missed"), (d) farewell ("Should we say goodbye?"), (e) reset ("Want fewer emails?"). One-line preview each.6. Onboarding sequence subjects
For a 5-email onboarding sequence, write subject lines that build a narrative arc: Day 1 welcome → Day 2 quick win → Day 4 dig deeper → Day 7 advanced → Day 14 community. Each ≤ 50 chars. Numbered prefix optional.7. Sales outreach subjects
Cold sales subject. Audience: `{persona}` at `{companySize}`. We solve: `{problem}`. Write 5 subjects ≤ 40 chars that don't pattern-match to spam. Skip "Quick question", "{first_name}, are you the right person?" — overused.Variables to swap: persona, companySize, problem
8. A/B test brief
I want to A/B test subjects. Brief: (1) Hypothesis, (2) Variant A, (3) Variant B, (4) Metric (open / click / reply), (5) Sample size needed, (6) Stop conditions. Don't test trivial changes (capitalisation) — test concepts.9. Mobile-truncation safe
Rewrite these subjects to survive 30-char mobile truncation. Move the verb / number / surprise into the first 30 chars. Output: original | mobile-safe | what survived.10. Brand-voice subject line check
Audit these subjects against our brand voice: {subjectList}. Mark each: in-voice (5) → off-voice (1). For off-voice, suggest one rewrite. Flag any that sound like every other newsletter.Variables to swap: subjectList
11. Localised subject line
Localise these subjects from English to `{lang}` without literal translation. Use the local idiom. Re-test for mobile truncation. Skip emoji if the locale's inbox renders them differently.Variables to swap: lang
12. Subject-line failure forensics
Last 5 subjects had open rate 18 / 22 / 14 / 28 / 16% (avg 18%). Diagnose: (1) Which subjects drove the spread, (2) Hypotheses (audience fatigue, topic mismatch, timing), (3) One experiment to run next. Output ≤ 200 words.Common mistakes
- Vague audience — “anyone who…” — output reads generic.
- No tone anchor — every variant comes back same flavour.
- No constraints — word count, banned phrases, length cap.
- Skipping examples — examples are the strongest signal for voice.
- Trusting first draft — AI lands on the safe middle.
- Overusing AI clichés (“In today’s fast-paced…”, “Unlock the power of…”).
- No edit pass on facts — output sometimes confidently wrong.
How to push results further
- Always supply 1-2 tone examples; “be friendly” alone is noise.
- Constrain ruthlessly — word count, banned phrases, must-include facts.
- Read aloud before publishing — if you stumble, rewrite.
- Cut adverbs and adjectives that don’t carry weight.
- AI for first 2 drafts, human edit for the third — and the third is what ships.
- Anchor in a real person from your customer list.
- Test the headline by reading it without the body — does the message survive?
Practical depth notes
Use these prompts as starting points, not final answers. For Email Subject Line Prompts: 12 Templates for Open Rates That Survive, the useful extra work is to replace every generic placeholder with a real constraint: audience, channel, length, brand voice, examples to imitate, and examples to avoid. Run at least two versions with different constraints, then compare the outputs side by side instead of accepting the first polished response.
A good result should pass three checks: it is specific enough that another person could reuse it, it avoids vague praise or filler, and it gives you an editable artifact rather than a broad suggestion. If the output feels generic, add one concrete reference, one forbidden pattern, and one measurable success criterion before rerunning the prompt. Before saving a prompt as reusable, test it on one realistic input and one edge case. The realistic input proves the template can produce the normal deliverable; the edge case shows whether it handles messy constraints, missing context, or an unusual audience. Keep the better output, but also keep the failed version with a note on what was missing. That small failure log is what turns a prompt collection from a list of nice sentences into a practical working library.
FAQ
- Subject length sweet spot?: 30-50 characters for most inboxes. Mobile truncates around 30-40.
- Emojis help?: Sometimes. They help open rates in some audiences, hurt in others. A/B test.
- First-name personalisation?: Use sparingly — over-used in cold email so it now signals spam.
- How many variants should I generate?: 5-7. Beyond, you’re evaluating noise, not concepts.
- Capitalisation matter?: Sentence case feels less spammy than Title Case for most newsletters.
- What’s a good open rate?: Highly category-dependent. 25%+ in many B2B contexts; less in mass consumer.
Related
- Newsletter prompts
- Email writing prompts
- Sales copy prompts
- Tone rewrite prompts
- Writing & Copywriting Prompts hub
Tags: #Prompt #Writing #Email #Subject line