5 subject line frameworks to try before sending your next email

This morning I led a training called Subject Line Mastery in a private community I manage.

As part of it, I pulled together a quick cheat sheet with 5 proven subject line frameworks you can use to come up with stronger ideas to get more people to open your emails.

I’m planning to make the training available you soon.

In the meantime, I wanted to share those frameworks with you, along with a prompt you can use to get AI to help you brainstorm subject lines using these same frameworks.

5 Proven Subject Line Frameworks

Use these repeatable formulas to craft subject lines that get opened. 

Each taps into a key psychological trigger—try multiple versions for every email!

1. Curiosity Gap

Trigger: Curiosity
How it works: Creates an open loop, making readers wonder what’s inside.
Examples:

• "The mistake that cost me 2,000 subscribers"

• "What I learned from 100 failed launches"

• "This one word tanked my open rates"

2. How-To Formula

Trigger: Clear Value
How it works: Offers practical, actionable advice.
Examples:

• "How to write emails your audience actually opens"

• "How to boost your open rates in 10 minutes"

• "How to get more replies without sounding salesy"

3. Number + Benefit

Triggers: Clear Value, Credibility
How it works: Uses numbers for specificity and promises a concrete benefit.
Examples:

• "7 subject lines that doubled my open rate"

• "3 quick tweaks for better email performance"

• "5 ways to grow your list this month"

4. Personal Touch

Trigger: Personal Relevance
How it works: Makes the email feel like it’s meant just for the reader.
Examples:

• [First name] this one’s for you"

• "You’re probably making this mistake"

• "What I wish someone told me earlier"

5. Urgency & Scarcity

Trigger: Urgency/Scarcity
How it works: Creates time or quantity pressure to drive immediate action.
Examples:

• "Last chance to grab the template"

• "Only 3 spots left for this workshop"

• "24 hours to catch the replay"

Try This Prompt:

You are an expert direct response copywriter, email marketing expert, and an expert in the psychology of buying. You understand how to use curiosity, urgency, clarity, and emotion to influence behavior — without sounding spammy or gimmicky.

I'm writing an email to my audience of [brief description — e.g. freelance designers, new coaches, startup founders].

Here is the full text of the email:

[paste your email here]

Based on the content, tone, and goal of the email, write 25 subject lines total using these 5 frameworks (5 per type):

Curiosity Gap – Tease something unexpected or thought-provoking

Examples:

• “The mistake that cost me thousands in one click”

• “What most people get wrong about welcome emails”

How-To – Promise a practical takeaway or learning

Examples:

• “How to 3x your open rate in 10 minutes”

• “How to make your emails feel personal (even to 10,000 people)”

Number + Benefit – Use a number to promise value or a result

Examples:

• “5 subject line tweaks that boosted our open rate 42%”

• “3 ways to grow your list this week (no ads required)”

Personal/Direct – Make it feel intimate, specific, or 1:1

Examples:

• “Nathan, this might be what you’ve been missing”

• “Let me be real with you for a sec…”

Urgency or Scarcity – Time- or quantity-based reason to open

Examples:

• “Last day to grab the free templates”

• “Just 3 spots left (and this won’t reopen)”

Instructions:

Keep them under 50 characters.

Sound natural, emotional, human.

Group results by framework.

Pick the ones that feel right for your voice and your audience.

Tweak them. Then test and send.

Let me know if you try the prompt or any of the frameworks.

I’d love to hear how it works for you.

Nathan

If you’re stuck on your newsletter, lead magnet, or AI setup, book a coaching session at this link and I’ll help you sort it out step by step so you can move forward with confidence and a plan.

Were you forwarded this email? Click here to subscribe.