Cold Email Subject Line Analyzer - Test & Optimize Your Subject Lines
Free cold email subject line analyzer. Check character count, spam triggers, and get a score based on proven best practices for cold outreach.
cold email subject line
email subject line tester
cold email subject line examples
Subject line analyzer
0 chars
0 words
No spam words
No emoji
Length recommendation
Enter a subject line to analyze.
This is a heuristic analyzer—deliverability also depends on your domain reputation, list quality, and message body.
Why your subject line makes or breaks your cold email
47% of recipients decide whether to open an email based on the subject line alone. For cold emails—where you have zero relationship with the recipient—that number is even higher.
A great cold email with a bad subject line never gets read.
How this analyzer works
Character count (optimal: 30-50 characters)
Word count (optimal: 4-7 words)
Spam trigger words detected
Capitalization issues
Personalization tokens present
Overall score based on cold email best practices
Cold email subject line best practices
Based on analysis of millions of cold emails:
| Factor | Best Practice | Why |
|---|---|---|
| Length | 30-50 characters | Displays fully on mobile |
| Words | 4-7 words | Easy to scan quickly |
| Capitalization | Sentence case | ALL CAPS = spam |
| Personalization | Use {{firstName}} or {{company}} | Increases open rates 20%+ |
| Questions | Sometimes effective | Creates curiosity |
| Numbers | Use sparingly | Can feel clickbaity |
Words that trigger spam filters
Avoid these in cold email subject lines:
“Free,” “Act now,” “Limited time”
“Congratulations,” “You've been selected”
“Click here,” “Buy now,” “Order now”
Excessive punctuation (!!!, ???)
ALL CAPS words
“Re:” or “Fwd:” when it's not a reply
High-performing cold email subject line formulas
1) The mutual connection:
{{mutualContact}} suggested I reach out2) The question:
Quick question about {{company}}'s approach to X3) The observation:
Noticed {{specific thing}} at {{company}}4) The direct ask:
{{firstName}}, 15 minutes this week?5) The pattern interrupt:
this is a cold emailSubject lines to avoid
“Following up” (on what? they don't know you)
“Quick question” (overused, feels manipulative)
“Exciting opportunity” (screams spam)
“I'd love to pick your brain” (what's in it for them?)
Anything misleading or clickbaity
Testing your subject lines
The best subject line is the one that works for your audience. A/B test by:
1. Sending the same email with different subject lines
2. Tracking open rates for each variant
3. Iterating based on data, not assumptions
Related tools
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