Email subject lines prompt: free ChatGPT template
Updated · By Robert Breen
Use this once the email is written and you need the line that gets it opened. AI subject lines lean toward clickbait: fake urgency, "you won't believe", a question the email never answers. This prompt writes options from the email itself, so every line is a promise the body keeps, and groups them by approach so you can test two different ideas instead of two near-identical lines.
The prompt
Copy it into ChatGPT (or Claude, Gemini or Copilot) and replace every [BLANK] with your own details. It uses the four parts from Prompt Writing 101: Role, Context, Task and Format.
Role: You are an email copywriter for [BUSINESS], whose readers are [AUDIENCE]. Context: The email is below. Our voice is [VOICE]. Subject lines must stay under [CHARACTER LIMIT] characters. Don't promise anything the email doesn't deliver. No all caps, fake urgency or fake reply prefixes. Task: Write ten subject lines grouped by approach: direct benefit, curiosity the email answers, a specific detail from the email, and a plain question. Give each a preview text line that adds information instead of repeating it. Then pick two to test against each other and say why. Format: Grouped lists, each line with its character count, preview text under 90 characters. Then a two-line recommendation. The email: [EMAIL TEXT]
Fill in the blanks
[BUSINESS]- Your business name and what you do.
[AUDIENCE]- Who reads your emails.
[VOICE]- Three or four words for how you sound.
[CHARACTER LIMIT]- 50 is a safe limit for phones.
[EMAIL TEXT]- The finished email, so every line comes from what it actually says.
Example, filled in
A made-up example from the free lesson n8n AI Agent Tutorial: Save Social Media Ideas to Google Sheets. BrightPath Marketing is the made-up agency in the AI social media agent lesson, which helps small and midsize businesses with SEO, ads, social media and websites. This month's newsletter grows one of the agent's post ideas into an email.
Role: You are an email copywriter for BrightPath Marketing, a digital marketing agency, whose readers are business owners and marketing managers at small and midsize businesses. Context: The email is below. Our voice is helpful, practical, professional and approachable. Subject lines must stay under 50 characters. Don't promise anything the email doesn't deliver. No all caps, fake urgency or fake reply prefixes. Task: Write ten subject lines grouped by approach: direct benefit, curiosity the email answers, a specific detail from the email, and a plain question. Give each a preview text line that adds information instead of repeating it. Then pick two to test against each other and say why. Format: Grouped lists, each line with its character count, preview text under 90 characters. Then a two-line recommendation. The email: Hi there, Most small businesses ask ChatGPT for ad copy and get something generic. The fix is giving it what it can't guess: who the ad is for, the one thing you offer, and the platform's character limit. Three steps we use with clients: 1. Paste your best ad and ask for five variations that keep the same offer. 2. Put the platform's character limits in the prompt. 3. Read every line for claims you can't back up before it runs. Reply with your industry and we'll send a prompt you can use this week. The BrightPath team
What a good answer looks like
- Specific lines pulled from the email, like "3 steps to better ad copy from ChatGPT".
- Curiosity the email pays off, such as "Why your ChatGPT ads sound generic", answered in the second sentence.
- Preview text that adds something, like "Reply with your industry for a free prompt."
- Two picks from different groups, so the test tells you which approach your readers prefer.
How to check it before you use it
An AI draft can sound right and still say something you never told it. Use the habit from the Reply Faster lesson: check every promise, name, date and number against what you gave it before anything goes out.
- Count characters yourself for the lines you pick. Models often miscount.
- Make sure every promise is in the email. If the line says "free prompt", the email must offer one.
- Leave statistics out of subject lines unless the email says where they came from.
- Look at the line on a phone, where it gets cut shorter.
Why this prompt works
Writing from the finished email ties each line to real content, and grouping by approach gives you a real A/B choice instead of ten versions of one idea. The character limit is a constraint the model can check against.
Practice it in the free lesson
n8n AI Agent Tutorial: Save Social Media Ideas to Google Sheets: Build an AI agent for BrightPath Marketing that generates social media post ideas and saves them to Google Sheets — chat trigger, AI Agent, system prompt, model, memory, and the Sheets tool. You do every step yourself in a practice copy of n8n, and nothing touches your real accounts.
Also useful: Build an n8n AI Agent That Plans Your Content Calendar
Terms used here
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