How to write subject lines people actually open
Meet your new AI wingman for titles that don’t suck
We all know the power of a good title. But on Substack, the right title isn’t just good—it’s essential.
I recently read a piece called The Headline Mistake Costing You Subscribers (a must-read), and it cracked open a topic we often overlook: the subtle but crucial difference between subject lines and headlines on Substack … and how to optimize both for better engagement.
That article got me thinking.
What if you could take everything in that post and turn it into a repeatable, automated system?
What if you could build a tool that helped you apply those insights consistently, every time you publish?
So that’s what I did.
I built a GPT.
And this article is the extended cut … a deeper dive into what the original article got right, what I wanted to add, and how my custom GPT helps you write smarter subject lines and headlines that get read, get shared, and get remembered.
1. What the Original Article Got Exactly Right
Let’s give credit where it’s due. The original article nailed several lessons that any Substack writer … new or seasoned … should internalize.
The Subject Line vs. Headline Distinction
Subject line = what shows up in your subscribers’ inboxes. It impacts the open rate.
Headline = what appears on your Substack page and in the app. It impacts SEO and shareability.
They’re similar, but not the same. They’re related, but they’re not interchangeable.
One gets the click. One gets the shares. Both need different strategies.
The Beta Testing Feature
Substack now lets you test different subject lines with a small slice of your list (say, 5%) before sending the winner to everyone. It’s a small change with a big impact.
It’s data-driven. It’s low-stakes. It’s built-in A/B testing without the hassle.
Tips for Subject Lines
Keep them short (under 60 characters).
Avoid emoji overload or oddball symbols.
Be human, but be clear … skip the vague poetry.
Create curiosity or urgency … but skip the spammy clickbait.
Tips for Headlines
Clarity over cleverness.
Specificity over abstraction.
Emotion over neutrality.
Align the headline with the story’s promise.
Capitalize for readability, not rigid grammar.
Use tools like Claude or ChatGPT to brainstorm … but let the final line come from you.
2. What I Wanted to Add (Or Felt Was Missing)
The original article was strong. But there were a few things missing … especially for creators who publish often and need a system that scales.
No clear workflow from draft → title test → SEO headline.
No automation to generate subject/headline/SEO bundles.
No personalization based on tone, voice, or audience.
No framework for scaling across multiple posts.
Great theory, little execution. Great advice, no system.
So I thought: What if we could take the advice; and build the system?
3. Introducing My Custom GPT for Substack Headlines: Newsletter Title Coach
I built a GPT that takes the headline wisdom from that post; and blends it with what I’ve learned as a writer, reader, and AI nerd.
What It Does
Distinguishes subject lines, headlines, and SEO titles
Writes short, snappy, on-brand subject lines
Crafts SEO-optimized headlines and meta descriptions
Gives you multiple options—so you can test, tweak, or choose
Adapts output to your tone, your topic, your platform
Outputs clean, copy-paste-ready content for Substack SEO settings
How It’s Different
It’s built for Substack.
It follows real journalism logic.
It’s focused on readability, clarity, and authenticity.
And it beta-tests tone, format, and structure—just like a good editor would.
4. How to Use the GPT to Write Stronger Titles (Step-by-Step)
Want better subject lines? Stronger headlines? Cleaner SEO?
Here’s how to use the GPT:
Step 1: Paste Your Post or Summary
Drop in your full draft or just 3–5 key sentences. It can handle both.
Step 2: Choose Your Title
Choose one and type YES to SEO bundle.
For example:
I choose: How to write subject lines people actually open
Write me SEO bundle now
Step 3: Check the SEO bundle
Step 4: Edit your Post and paste the results
Go to the Settings page of your Post and find SEO options:
5. Why This Matters: From Creative Chaos to Consistent Results
We don’t struggle to come up with a title.
We struggle to come up with the right title … again and again, without burning out.
That’s where this GPT comes in.
It gives you clarity; on what kind of title you’re writing and why.
It gives you speed; great drafts in seconds.
It gives you consistency; your voice, elevated.
It gives you results; more opens, better shares, stronger SEO.
This isn’t about replacing creativity.
It’s about reinforcing it; with structure, strategy, and style.
Conclusion: Give It a Try (Your Titles Will Thank You)
The original article opened my eyes to how much power we pack into a single line of text … and how that line can make or break a post.
My GPT takes that insight and turns it into action: better subject lines, better headlines, better SEO … all in a few clicks.
✅ Want to test your next title?
✅ Want to audit your archive?
✅ Want to stop guessing and start publishing with confidence?
Try it here. (yes it is FREE)
You’ve got something important to say … make sure people click to read it.