Write Email Subject Lines with AI
To write email subject lines with AI, give @vustbot your email's core message, audience and goal, and ask for 10 subject lines under 50 characters. Then regenerate the same brief with a second model — GPT-5.6 and Claude write noticeably different hooks — and A/B the two strongest. All in one Telegram chat, paid per action.
The tools ranking for this query optimize their own templates. The underused move is multi-model A/B: two frontier models given the same brief produce genuinely different hook styles — and no P.1 tool page does that today.
What the AI does in this scenario
- 10 options per run, length-capped for mobile preview
- Multi-model A/B: same brief to GPT-5.6 and Claude, different hook styles
- Goal-aware: open-rate tease vs announcement clarity are different asks
- Spam-trigger words avoided on request
- Per-action pricing — test batches without a tool subscription
Worked example: write email subject lines with ai
01Input — what you paste
Email: our project-management app now has offline mode. Audience: existing free-tier users. Goal: feature-announcement opens, no clickbait.
02Output — what comes back
1) Offline mode is here — plan anywhere. 2) Your boards now work without wi-fi. 3) New: full offline editing, synced later. 4) Trains, planes, basements: boards work now. 5) The most-requested feature just shipped. …(+5 more, each ≤50 chars)
How to write email subject lines with ai — step by step
- 1Brief the message, audience and goal
One message to @vustbot: what the email says, who receives it, and whether you're chasing opens, clicks or clarity. The goal changes the hook style more than the topic does.
- 2Ask for 10 under a hard length cap
"10 subject lines, each under 50 characters, no clickbait, no spam-trigger words" — the cap keeps them mobile-safe, the batch gives you real choice.
- 3A/B across models, then across readers
Regenerate with a second model in the same chat and shortlist the strongest from each. Ship the top two as an actual A/B test — the models gave you the variance for free.
AI vs doing it manually
A human who knows the list writes ONE great subject line; AI writes ten plausible ones in seconds. The manual craft still matters at the shortlist step — you know that your audience hates emoji or that "free" tanks your deliverability. Use AI for the batch and the variance, yourself for the veto. Where AI clearly wins: the tenth send of the month, when your own hooks have converged to a formula.
The prompt to copy
Write 10 email subject lines for this email: [CORE MESSAGE]. Audience: [WHO]. Goal: [OPENS/CLICKS/CLARITY]. Rules: each under 50 characters; no clickbait; no spam-trigger words (free!!!, act now); vary the mechanism across the 10 (curiosity, benefit, news, question, specificity).
Frequently asked questions
Why generate subject lines with two different models?
Because hook style is a model fingerprint: given the same brief, GPT-5-class output leans punchy-newsy while Claude leans specific-and-warm. Two models = two genuinely different candidate pools for the same A/B slot — variance you'd otherwise pay a copywriter for.
What subject-line length should I ask the AI for?
Cap at 50 characters in the prompt: mobile clients truncate around there, and the cap forces the model to front-load the hook. If your audience skews desktop, 65 is safe — but write the cap into the prompt either way, or the model will ramble.
Can AI subject lines hurt my deliverability?
Only if you let spam-trigger phrasing through — so ban it in the prompt ("no spam-trigger words") and keep the veto step human. The prompt template on this page includes that rule by default.
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Try it on your real task
The welcome bonus covers a first run — send the prompt above with your own facts and judge the output yourself.
Open @vustbot