Analyzer · 100% free, no signup · Updated May 2026
Score your subject line before you hit send.
A free email newsletter subject line tester that scores subject lines on length, sentiment, spam-trigger words, curiosity gap, and preview-text alignment. Output: 0-100 score with 3 rewrite suggestions targeting the weakest dimension.
Paste your subject line + pick your audience. The tester scores 0-100 on five dimensions (length, power-words, urgency-vs-curiosity balance, emoji weight, specificity) and suggests 3 rewrites that fix the lowest-scoring dimension.
Subject line
43 characters · ideal ≤ 50 for mobile preview
Composite score
67/100
Length
100/100
43 chars · target ≤ 50
Power words
30/100
1 power-word hit · target ≥ 1
Curiosity / urgency
40/100
1 curiosity, 0 urgency
Emoji
90/100
0 emoji · audience-tuned
Specificity
70/100
Numbers + names lift opens 20-30%
3 rewrites (fixing weakest dim: power)
- Add a power word: "Why Why I cut 4 features from my SaaS this week"
- Add urgency: "Why I cut 4 features from my SaaS this week (today only)"
- Add curiosity: "The truth about why i cut 4 features from my saas this week"
Who this is for
Newsletter writers and B2B email marketers who want a second pair of eyes on the line that determines whether the email gets opened.
The problem this solves
Subject line decides 80% of open-rate. Most tools give you a vague "good" or "bad" — the tester actually scores each of the five things that matter (length under 50 chars / power-word density / curiosity-gap vs urgency / emoji weighting / specificity) and rewrites for the weakest one.
Newsletter subject lines between 30-50 characters achieve approximately 18-25% higher open rates than subject lines over 60 characters — yet 47% of newsletter operators ship subject lines over 60 characters.
Source: Beehiiv Newsletter Performance Report 2024 + ConvertKit Subject Line Study 2024
How to use it
- 01
Paste your subject line
The exact text. Including emojis if you use them. The tester counts every character.
- 02
Pick your audience
B2B operators / B2C creators / Enterprise / Indie / Newsletter (general). Each audience weights the 5 dimensions differently.
- 03
Read the 0-100 score
Composite score + breakdown across length, power-words, urgency/curiosity, emoji, specificity. Each dimension shows what's right and what to fix.
- 04
Apply the 3 rewrites
Three rewrites that fix the weakest dimension while keeping the message. Pick the one that fits your voice.
What you get
- ✓ 0-100 composite score
- ✓ 5-dimension breakdown (length, power-words, urgency/curiosity, emoji, specificity)
- ✓ 3 rewrites targeting the lowest-scoring dimension
- ✓ Audience-aware weighting — B2B ≠ B2C scoring
Frequently asked
What's the ideal subject line length?
30-50 characters. Mobile email clients truncate around char 35-50. Anything over 60 gets cut off in most inbox previews.
Are emojis in subject lines still effective?
Mixed. One leading emoji can boost opens 5-15% in B2C niches. Multiple emojis or B2B contexts: emojis actively hurt opens.
Should I use ALL CAPS or punctuation marks?
No. ALL CAPS triggers spam filters and reduces opens 30-40%. One question mark or exclamation is fine; multiple "!!!" gets filtered.
What spam triggers should I avoid?
"Free", "Act now", "Limited time" — these trigger Gmail's promo-tab classifier. Words like "amazing", "incredible", "unbelievable" also lower opens.
Does preview text matter?
Yes, hugely. The first 35-90 chars of the email body appear as preview text. The generator suggests preview text that compounds with (doesn't repeat) the subject line.
Related tools
Author + maintainer
Adrian Berisha — Founder of Clipflow. Indie SaaS builder shipping creator tools full-time since 2024. All tools and benchmarks on this page are reviewed quarterly. Last review: May 2026.
@clipflow on X · LinkedIn · hi@clipflow.to
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