Email Subject Line Analyzer

The Email Subject Line Analyzer scores a subject line, and its preview text, out of 100 before you hit send. It checks length, spam-trigger phrases, all-caps words, punctuation, word count, specificity, emoji and fake reply prefixes, then shows how the line might look in a phone inbox. It is free, it runs in your browser, and the first time you use it we ask for your email to show the results.

It is built for founders and B2B marketers who write their own newsletters, nurture emails and product updates. You get a plain reason for every point, not a black-box grade.

Key takeaways

• Aim for 80 or more. That clears the common problems; it does not guarantee opens.
• Keep the subject between 25 and 50 characters and front-load the words that matter.
• Write preview text every time. Without it, inboxes show the first line of your email.
• Never start with Re: or Fwd: unless the email is a real reply or forward. Gmail's own sender guidelines say so.
• Deliverability comes first. No subject line fixes missing SPF, DKIM or DMARC.

How the email subject line analyzer works

The tool applies a fixed rubric. The code is the same for everyone and nothing is sent to an AI model. Here is exactly what it checks and how many points each check is worth.

Check	Max points	Full points when	What costs you points
Length	25	25 to 50 characters	15 to 24 or 51 to 65 characters scores 15; anything shorter or longer scores 5
Spam-trigger phrases	20	None of our list of 28 phrases	Each phrase found takes off 8 points
All-caps words	15	No word of 3+ letters in capitals	One such word scores 8; two or more score 0
Punctuation	10	No exclamation marks, fewer than 2 symbols	One exclamation mark scores 6; more, or 2+ symbols ($ % * # @), score 0
Word count	10	4 to 9 words	Fewer or more words score 5
Specificity	10	Contains a number, a question or a personalization tag	None of the three scores 4
Emoji	5	0 or 1 emoji	2 or more score 0
Preview text	5	Present and different from the subject	Missing or identical scores 0
Re: or Fwd: prefix	penalty	Not present	Starting with Re:, Fw: or Fwd: takes off 15

The spam list includes phrases such as free, guarantee, act now, urgent, click here, buy now, limited time, 100%, $$$, congratulations and no obligation. Matching is whole-phrase, so freedom doesn’t trigger free.

The personalization check recognizes the merge-tag formats of common email tools: {{first_name}}, *|FNAME|*, [first name], [company] and %name%.

Length is counted in characters as you see them, so an emoji counts as one character.

How to read your results

You get a score, a verdict, a phone-style preview and a row for every check, marked Good, Improve or Fix.

Score	Verdict	What it means	What to do
80 to 100	Strong	No serious problems in the rubric	Pick your two strongest lines and A/B test them
60 to 79	Good, with fixes	One or two rows are costing you	Fix any red row, then rerun
0 to 59	Needs work	Several problems, often caps, spam phrases or length	Rewrite from the reader’s benefit, not the excitement

The inbox preview is approximate. Each email app trims subjects to fit the screen and its own layout, so treat the preview as a check on what comes first, not a pixel-perfect render.

A worked example, scored by the tool

We ran three versions of the same announcement through the analyzer. These are the tool’s actual results.

Version 1: “🚀 HUGE NEWS!!! Don’t miss our AMAZING new features” (no preview text)

• Length: 50 characters, 25/25.
• Spam phrases: none, 20/20.
• All-caps words: HUGE, NEWS, AMAZING, 0/15.
• Punctuation: 3 exclamation marks, 0/10.
• Words: 9, 10/10.
• Specificity: no number, question or tag, 4/10.
• Emoji: 1, 5/5.
• Preview text: missing, 0/5.

Total: 25 + 20 + 0 + 0 + 10 + 4 + 5 + 0 = 64, Good with fixes. Notice that the length was fine. The capitals and exclamation marks cost 25 points between them.

Version 2: “Your audit report now shows AI search visibility” (no preview text)

The capitals and punctuation are gone, so those rows score 15 and 10. “AI” has only two letters, so it isn’t flagged. Total: 25 + 20 + 15 + 10 + 10 + 4 + 5 + 0 = 89, Strong.

Version 3: the same subject, plus the preview text “See which AI answers cite you, and which cite competitors”

The preview text adds 5 points: 94, Strong. The only row left at Improve is specificity. Adding a number (“Your audit report now tracks 4 AI search tools”) would take it to 100, but only if the number is true.

The jump from 64 to 94 came from removing noise, not from adding clever words. That is the usual pattern.

Best practices for B2B subject lines

Before you send

• Say what's inside. "Your Q4 pipeline review, in 5 minutes" beats "Big update!"
• Put the most important three or four words first, because phones cut the end.
• Write preview text that adds a second reason to open, not a repeat of the subject.
• Use a real number only when it is accurate and checkable.
• Personalize with care. A broken merge tag ("Hi {{first_name}}") is worse than none, so send yourself a test.
• Match the subject to the email. A subject that oversells gets opens once, then complaints.
• Keep one voice. If your brand doesn't use emoji anywhere else, don't start in the inbox.

• 5,000 messages a day to Gmail accounts is the point where Google applies its bulk-sender rules Google, Gmail email sender guidelines, 2026
• 0.3% user-reported spam rate in Postmaster Tools that Gmail tells senders to stay below Google, Gmail email sender guidelines, 2026
• $53,088 maximum penalty per email that breaks the CAN-SPAM Act, which requires subject lines to reflect the content Federal Trade Commission, CAN-SPAM Act compliance guide, 2026

Two rules in those sources line up directly with the rubric. Google’s sender guidelines tell senders not to start subject lines with Re: or Fwd: unless the message is an actual reply or forward. The FTC’s guide says the subject line must accurately reflect the content of the message. That is why the analyzer treats a fake reply prefix as a penalty, not a style choice.

The spam-rate limit matters more than any single word. If readers feel tricked by a subject, they report the email, and those reports count against every email you send afterward. Our B2B email deliverability guide covers the full Gmail, Yahoo and Outlook rules, and our glossary entry on SPF, DKIM and DMARC shows example records.

Common mistakes

Myth vs fact

MythA list of banned spam words decides whether your email reaches the inbox.

FactSender reputation, authentication and complaint rates matter far more. Google's sender guidelines focus on SPF, DKIM, DMARC, one-click unsubscribe and spam rates, not vocabulary. Trigger phrases matter because they make readers suspicious, and suspicious readers press Report spam.

Myth vs fact

MythA higher open rate proves the subject line worked.

FactApple Mail Privacy Protection loads email content in the background, so opens are inflated for Apple Mail users. Judge subject lines on clicks, replies and conversions, using a proper A/B test with a large enough sample.

Myth vs fact

MythLonger subject lines give you more room to persuade.

FactOn a phone the inbox cuts long subjects, so the end is often never read. Shorter subjects with the key words first, plus preview text, carry the same message in the space you actually get.

A few more we see often:

• Writing the subject last, in a hurry. It is the line most people read. Draft three, score them all.
• Leaving the preview text to chance. Without it, many inboxes show “View this email in your browser” or the alt text of your logo.
• Copying consumer tactics into B2B email. Countdown emoji and ALL-CAPS urgency look out of place in a finance manager’s work inbox.
• Testing two lines that are almost the same. Test different ideas, such as a benefit versus a question, so the result teaches you something.

I use a score as a starting point, never the final word. The better test is the inbox itself: put your subject and preview text next to the emails your buyer actually gets that morning, and ask whether yours would earn the click. In B2B, plain and specific usually wins. Tell people what's inside and why it matters to them now.

What the analyzer can’t tell you

The rubric catches common problems. It cannot know your audience, your sender reputation or whether your list opted in. It does not check deliverability, and it does not predict opens.

Use it as a pre-send check, alongside a test send to Gmail and Outlook accounts, a look at your Postmaster Tools spam rate, and a real A/B test on your list. If your emails are landing in spam regardless of the subject, start with authentication and list hygiene.