Email Subject Line Analyzer
Score any subject line 0-100 across 8 signals: length, word count, spam triggers, sentiment, emoji, CAPS ratio, personalization, and power words. Free, instant, unlimited use. Type below to score live.
Spam-trigger words detected
How to use the analyzer
- Type or paste your subject line in the input above. The score updates live as you type (300ms debounce).
- Read the breakdown - green dots are good, amber are borderline, red need fixing.
- Apply the advice - usually 1-2 changes lift the score 10-20 points.
- Re-type and ship.
What each signal measures
Length - character count. Sweet spot 30-50 chars. Mobile clients truncate around 30-40, desktop Gmail shows ~70.
Word count - concise reads as confident; verbose reads as unsure. 5-9 words is the open-rate sweet spot across multiple research datasets.
Spam triggers - match against ~150 high-impact words distilled from SpamAssassin's URI/SUBJECT rules and the mailmeteor/spam-words list. One match is borderline; two or more is high risk.
Sentiment - AFINN-style scoring across positive/negative words. Marketing emails skew positive; subjects with mildly positive language outperform neutral ones, and outperform overtly hyped ones.
Emoji - one is fine, two borderline, three or more triggers spam heuristics in Gmail and Outlook.
CAPS ratio - anything over 50% reads as shouting. Below 20% is natural.
Personalization - bonus when a token like [FirstName], {{name}}, %FNAME%, or *|FNAME|* is detected. Personalized subjects open 10-20% better on average.
Power words - bonus for verbs and adjectives that lift CTR without triggering spam filters: discover, introducing, unlock, finally, announcing.
FAQ
What makes a good email subject line?
Concise (30-50 characters, 5-9 words), specific to one outcome, and free of spam-trigger words. Add a personalization token like [FirstName], use one emoji at most, keep CAPS under 20%. Power words like "discover", "introducing", "unlock" lift open rates without triggering spam filters.
How long should an email subject line be?
30-50 characters is the sweet spot. Mobile clients (where 60%+ of email opens happen) truncate around 30-40 chars; desktop Gmail shows ~70 chars. Keep the most important word in the first 30 chars so it survives mobile truncation. Anything over 70 characters will truncate everywhere.
Which words trigger spam filters?
Money words (free, $$$, cash, save), urgency words (act now, last chance, urgent), guarantee words (100%, no risk, money back), and hype (amazing, incredible, miracle). Spam filters use weighted scoring across thousands of signals - one trigger word usually doesn't tank delivery, but combinations do. The analyzer here uses a curated list of ~150 highest-impact triggers distilled from SpamAssassin and mailmeteor.
Should I use emoji in email subject lines?
One emoji is fine and can lift open rates 5-15% in B2C. Two is borderline. Three or more reads as spam to both filters and users. Pick a single emoji that matches the message, place it at the start or end (not the middle), and skip purely decorative ones. Outlook strips emoji from preview panes; don't rely on them as the only differentiator.
Does the score predict open rates?
Loosely. The score is a sum of well-known deliverability and copywriting signals - high scores correlate with better delivery and click-through, but actual open rates depend on your sender reputation, list quality, send time, and the audience's existing relationship with you. Treat the score as a hygiene check, not a prediction.
What are personalization tokens?
Placeholders that your ESP swaps for subscriber data at send time - [FirstName], {{name}}, %FNAME%, *|FNAME|* (Mailchimp), and similar. Subject lines with the recipient's first name see 10-20% higher open rates on average. The analyzer detects all common token formats and gives a bonus when one is present.
Does the analyzer work for non-English subject lines?
Partially. Length, word count, emoji count, CAPS ratio, and personalization-token detection work in any language. Spam triggers and sentiment scoring are English-only - the wordlists are English. Non-English subjects will get inflated scores in those two categories.
Is the score saved or shared?
No. Each analysis hits a Cloudflare Worker that scores your subject line and returns the result - nothing is logged, stored, or correlated. You can use the tool unlimited times without an account.
Build the email this subject line goes into
MiN8T's editor is the natural next step - paste your subject in, design the body, ship to any ESP. No tab-juggling.
Open MiN8T Editor →