βοΈ Email Subject Line Tester
Score your subject line before you hit send.
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Subject Score
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How to Use This Tester
Type or paste your subject line and the tester scores it from 0 to 100 across five factors: length, spam trigger words, all-caps usage, exclamation marks, and personalization. You also see exactly how the subject looks when truncated on mobile and desktop inboxes, plus a flag list of everything worth fixing.
Type your subject line. The character count and score update as you type.
Read your score: Excellent (80+), Good (60 to 79), Fair (40 to 59), or Poor (under 40).
Check the mobile and desktop truncation previews. If the key words fall past the cutoff, rewrite so they come first.
Work through the flags: remove spam triggers, drop the caps lock, and calm the exclamation marks.
The Scoring Rubric
The rubric targets the two jobs a subject line has: survive the spam filter and earn the open. Length carries the most structural weight after spam because truncation is the silent killer: a brilliant subject that gets cut at 30 characters on a phone never gets its chance. Spam triggers are penalized heavily because they attack deliverability itself; an email in the spam folder has an open rate of zero. All caps and stacked exclamation marks are classic desperation signals that both filters and humans distrust. The personalization bonus rewards the two cheapest lifts in email: speaking directly to the reader and asking a question that creates an open loop.
Worked Example
Bad: "URGENT: You WON a FREE vacation!!!" (34 characters). Length is fine at 30 out of 30. Spam triggers: "urgent", "won", and "free" are all on the trigger list, 3 x 12 = 36, so 35 minus 36 floors at 0 out of 35. All caps: 14 of 25 letters are uppercase (56 percent), so 0 out of 10. Exclamation marks: 3 earns 0 out of 10. Personalization: "you" appears, so 8 out of 15. Total: 38 out of 100, "Poor". Mobile preview cuts it to "URGENT: You WON a FREE vacati...", which somehow looks even worse. Good: "Your order ships Thursday" (25 characters). Length: 30 out of 30. Spam triggers: none, 35 out of 35. All caps: one capital letter, 10 out of 10. Exclamation marks: none, 10 out of 10. Personalization: "your" appears, 8 out of 15. Total: 93 out of 100, "Excellent". Notice the good subject wins by being calm, specific, and short, not by being clever.
Subject Lines That Get Opened
Put the news in the first 30 characters, because that is all many phones show. Make one promise per subject; cramming two ideas in reads as noise. Be specific instead of clever: "Your order ships Thursday" beats "Exciting news inside!" every time, because specificity is believable. Avoid RE:, FWD:, and fake urgency unless the email genuinely is a reply, a forward, or urgent; readers learn fast. Send yourself a test and read the subject on your phone lock screen: if it does not make sense out of context, rewrite it. Finally, A/B test subject lines on a slice of your list before the full send; a 10 percent test group costs you nothing and teaches you what your audience actually opens.
Frequently Asked Questions
What is a good email open rate?
It varies widely by industry, list quality, and email type. Most marketing emails land between 15 and 30 percent, while transactional emails like order confirmations often exceed 50 percent. Rather than chasing a universal benchmark, track your own trend: if your opens climb after you start testing subject lines, the work is paying off. A sudden drop usually signals a deliverability problem, not a copy problem.
How long should a subject line be?
Keep it to 41 characters or fewer. Most email is opened on phones, and mobile inboxes show roughly 30 to 41 characters before cutting the subject off, depending on the device and app. Desktop clients show around 60. This tester previews both cutoffs so you can see exactly where your subject gets truncated and front-load the important words.
Which words trigger spam filters?
Classic triggers include free, guarantee, winner, urgent, act now, cash, prize, double your income, no risk, and anything with $$$ or excessive punctuation. Modern spam filters weigh engagement history more than single words, but trigger words still hurt, especially for new senders without a reputation. This tester flags more than 30 common triggers so you can rewrite before you send.
Do emojis in subject lines help?
Sometimes. In consumer and lifestyle emails, a single relevant emoji can lift opens by standing out in a crowded inbox. In B2B or formal contexts, emojis can look unprofessional and hurt trust. Rules of thumb: never more than one, never replace words with emojis, and always test with your own audience, since emoji effects vary a lot by demographic. This tester does not score emojis, so use your judgment.
Should I personalize subject lines?
Yes, when it is genuine. Including the recipient name or referencing something specific to them consistently lifts open rates, because the subject signals "this email is for me." What backfires is fake personalization: "Re: your account" on a cold email destroys trust the moment it is opened. This tester awards bonus points for "you" and "your" phrasing, which captures most of the benefit without needing merge tags.