Free Subject Line Checker — Email Subject Line Tester (2026) | AU
Free email subject line checker. Score open-rate potential, catch spam triggers, preview mobile rendering, and get AI-rewritten subject lines instantly. Optimised for Australian marketers.
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Why use this tool?
Stop wasting time doing this manually. Let AI handle the heavy lifting.
Boost Open Rates
Identify the words that trigger curiosity and get your emails opened.
Spam Check
Avoid spam trigger words that send your emails straight to the junk folder.
Mobile Optimization
Preview how your subject line looks on mobile devices before you send.
How Our Subject Line Checker Scores Your Copy in 2026
This free email subject line tester grades your copy 0–100 against four real-world ranking factors used by Gmail, Outlook, and Apple Mail. It then rewrites your line in three different angles so you can A/B test on the spot. Your subject line is the gatekeeper of your content — it doesn't matter how amazing your email body is if no one clicks to see it.
Unlike older subject line checker tools that rely on a fixed word blacklist, ours uses AI to evaluate emotional pull, audience fit, and curiosity gap on every test.
The 4-factor scoring rubric
Under 40 chars = full mobile preview. 40–60 = safe on desktop. Over 60 = truncated on phones.
One clear promise, no jargon. The reader knows what they get if they open.
Open loop or surprising angle. Gives a hint without revealing everything.
No spam triggers, no ALL CAPS, no excessive punctuation. Sender reputation stays intact.
Grade bands: 0–49 Weak · 50–69 Okay · 70–84 Strong · 85–100 Excellent.
3 Golden Rules for Email Subject Lines
1. Mobile First
Over 60% of emails are opened on mobile devices. Most phones truncate subject lines after 35-40 characters. Keep your most important words at the beginning.
2. Avoid Spam Traps
Email providers like Gmail use sophisticated AI to filter spam. Aggressive sales language ("BUY NOW", "FREE!!!") hurts your sender reputation and deliverability.
3. Invoke Curiosity
The "curiosity gap" is a powerful psychological trigger. Give a hint of what's inside without revealing everything to compel the click.
The Danger Zone: 7 Spam Trigger Words to Avoid
Email service providers (ESPs) heavily penalize emails that sound like scams. Avoid these words in your subject lines whenever possible:
- ✗ "Free" / "100% Free" (Use "Complimentary" instead)
- ✗ "$$$" or "Cash" (Use "Credit" or specific amounts)
- ✗ "Guarantee" / "Risk-Free" (Overused by scammers)
- ✗ "Urgent" / "Act Now" (Unless it actually is)
- ✗ "Winner" / "Won" (Classic lottery scam language)
- ✗ "Click Here" (Generic and suspicious)
- ✗ ALL CAPS (Counts as "shouting" and spammy)
Optimal Subject Line Length by Device
| Device / Platform | Visible Characters | Recommendation |
|---|---|---|
| iPhone (Portrait) | ~41 characters | Critical Zone |
| Android (Portrait) | ~30-40 characters | Critical Zone |
| Gmail (Desktop) | ~70 characters | Safe |
| Outlook (Desktop) | ~60 characters | Safe |
*Tip: Always front-load your value. Put the most compelling keywords in the first 30 characters to ensure they are seen on every device.
100+ Subject Line Examples (Swipe File)
Need inspiration? Here are eight proven angles — each with three real-world examples you can copy, tweak in the subject line checker above, and ship today.
- "Uh oh, your prescription is expiring" (Warby Parker)
- "Tonight only: A denim lover's dream" (Gap)
- "Last chance to see this..."
- "How to get more done in less time"
- "Steal these email templates"
- "Your 5-step plan for better sleep"
- "Hey [Name], quick question?"
- "I thought you might like this..."
- "Are you free on Tuesday?"
- "10 weird hacks that actually work"
- "5 reasons you're not losing weight"
- "3 things to avoid in 2026"
- "This changed everything for us"
- "What happened when we deleted 80% of our content"
- "You're probably doing X wrong"
- "Are you guilty of this content mistake?"
- "What if your best client left tomorrow?"
- "Quick: what's your morning routine?"
- "+42% open rate (here's how)"
- "Save 7 hours this week with one tweak"
- "$3,400 in MRR from a single subject line"
- "I almost shut the business down last night"
- "My weirdest customer call ever"
- "The day I deleted my Instagram"
How to A/B Test Your Subject Lines
The only way to know what works for your audience is to test. Most email marketing platforms allow you to run A/B tests. Here is a simple framework:
- Isolate one variable: Test length vs. length, or question vs. statement. Don't change everything at once.
- Send to a small segment: Send version A to 10% of your list and version B to another 10%.
- Wait for significance: Wait 2-4 hours to see which version has the higher open rate.
- Send the winner: Send the winning subject line to the remaining 80% of your list.
Optimize Your Entire Strategy
Great email marketing works hand-in-hand with great social media. Use our other free tools to align your messaging across all channels.
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Frequently Asked Questions
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