What does the Subject Line Analyzer do?
It scores one email subject line from 0 to 100 and tells you why it lost every point it lost. You type the line. The score, seven checks and two inbox previews update with each key you press. There is no Analyze button and nothing to submit.
Try it with "URGENT: Last chance to get 50% off EVERYTHING!!!". The Subject Line Analyzer returns 40, graded Weak. Three rows explain the 60 missing points. Capital letters fail, because exactly half of the 34 letters are capitals. Punctuation fails, because there are three exclamation marks. Spam words warn, because "urgent" is on the list. The phone preview shows what a reader sees on a small screen: "URGENT: Last chance to get 50% off EVE…"
That is the whole job. It doesn't write subject lines, guess your open rate, or ask who you are. Your line is scored inside your browser tab and never sent anywhere. There's no account, no email field and no cap on how many lines you test.
That last part matters more than it should. Search for a subject line tester and all nine of the top results are run by companies selling an email platform subscription. A tester at the front door of a paid platform is a funnel with a score attached. This one is just the score.
When you'll use a subject line tester
Most people land here a few minutes before a send. Some common moments:
- The weekly newsletter. It's 9:55, the send goes at 10:00, and you've written the line three ways. Paste each one and keep the version with no red rows. It takes less time than rereading the draft.
- A sale or launch email. Promotional lines are where caps, exclamation marks and words like "free" pile up. The checker shows when you've stacked two or three of them, which is the point where a reader stops seeing an offer and starts seeing an ad.
- Cold outreach. A short, plain line usually beats a clever one when the reader doesn't know you. The words check catches lines that are too long to read at a glance. The fake reply check catches the "Re:" trick before you send it to 200 strangers.
- Templates with merge tags. If your line starts with
{{first_name}}, you can't eyeball the length. The tool counts each tag as a four-letter name, so the number matches what a reader will see. - Reviewing someone else's line. "It feels spammy" starts an argument. "It scores 55 because of three emoji and a word in all caps" ends one.
The Subject Line Analyzer works the same whether you're a freelancer emailing 40 clients, a student group announcing a bake sale, or someone at a large company drafting the quarterly update.
How the Subject Line Analyzer scores a line
Every line starts at 100. Seven checks each return pass, warn or fail. Each warning costs 10 points and each failure costs 25. The score never drops below zero, and nothing else goes into it. No hidden weighting, no model guessing at tone. If the score is 75, one row says Fail and the other six say Pass.
| Check | Pass | Warn | Fail |
|---|---|---|---|
| Length (characters) | 30–50 | 15–29 or 51–70 | Under 15 or over 70 |
| Word count | 4–9 | 2–3 or 10–12 | 1, or 13 and up |
| Capital letters | Anything else | A word of 4+ letters, all capitals | 8+ letters and half or more are capitals |
| Punctuation | Anything else | — | Two or more "!" or a "$$" |
| Spam words | None | One | Two or more |
| Emoji | 0–1 | 2 | 3 or more |
| Fake reply | Anything else | — | Starts with "re:", "fw:" or "fwd:" |
The grade is a label on the number: 90 and up is Strong, 70–89 is Good, 50–69 is Needs work, and under 50 is Weak.
A few counting rules are worth knowing. Characters are counted the way you see them on screen, so a flag or a family emoji counts as one. A word is any chunk between spaces that holds a letter or a digit, so a lone emoji or dash isn't a word. Spam words match whole words only, and the longest phrase wins. "100% free" is one hit, not two. The full list has 27 entries, from "act now" to "you have been selected".
The phone preview shows the first 38 characters and the desktop preview shows the first 70. Those are rough averages. Real inboxes vary with screen size, font and sender name, so read the cut as "about here", not as an exact limit.
Examples: one line, rewritten to 100
Here is the sale line from above, rewritten twice. Every number comes from the tool.
| Subject line | Score | What changed |
|---|---|---|
| URGENT: Last chance to get 50% off EVERYTHING!!! | 40 Weak | Caps fail, punctuation fail, "urgent" warns |
| Last chance: 50% off everything ends tonight | 100 Strong | All seven pass, but the phone cuts it at "ends t…" |
| Last chance: 50% off ends tonight | 100 Strong | 33 characters, so "tonight" survives on a phone |
The second row is the lesson. A perfect score didn't mean the line worked. The deadline, the one word that creates the urgency, sat past the phone cut. The score can't know which word matters. The preview shows you, and that's why it sits under the score.
A wider spread of lines, run through the same checks:
| Subject line | Score | Where the points went |
|---|---|---|
| {{first_name}}, your March numbers are in | 100 Strong | Nowhere. Counted as 31 characters, previewed as "Alex, your March numbers are in" |
| Free shipping on every order this weekend | 90 Strong | One spam word ("free") warns |
| Congratulations! You're a winner | 75 Good | Two spam words fail |
| Free gift, free shipping, free returns | 75 Good | "free" three times fails |
| Fwd: the pricing deck you asked about | 75 Good | Fake reply fails |
| Quick question | 65 Needs work | 14 characters fails, 2 words warns |
| 🔥🔥 Our BIGGEST sale ever 🔥 | 55 Needs work | 3 emoji fail, "BIGGEST" warns, 26 characters warns |
| Your 2026 tax documents are ready, plus three deadlines you should know about | 50 Needs work | 77 characters fails, 13 words fails |
Dropping two of the fires and lowering "BIGGEST" turns that 55 into "🔥 Our biggest sale ever", which scores 90. The only thing left is a short-line warning at 23 characters.
Where the score gets it wrong
A subject line checker that follows fixed rules will sometimes follow them off a cliff. Here is where this one does, so a red row doesn't send you rewriting a line that was fine.
Words that only look like spam
Spam matching is whole-word, so "Cashews are back in stock this week" scores 100. A hyphen isn't a letter, though. "Cash-back is back this week" finds "cash" and drops to 80. If the word is part of your product name, keep it and accept the warning.
A colon after "Re"
The fake reply check looks at the first characters only. A real reply fails too: "Re: Thursday's call" scores 55. So does a name like "Re:design week starts Monday", at 65, while "Redesign week starts Monday" scores 90. If the email genuinely continues a thread, ignore the row.
Things the list doesn't know
"Last chance" isn't on the spam list, so urgency can pass every check. Every merge tag counts as "Alex", so {{company}} is four characters even if your client is called something much longer. The spam list is English, so a line in another language can pass the spam row for no good reason.
If your score looks wrong, read the row that cost you points before you rewrite anything. Each row names its rule. A warning you understand and choose to keep beats a rewrite that makes the line worse.
And the big one: the score knows nothing about who is sending. Whether your mail lands in the inbox depends far more on your domain's history and whether readers open or delete you. Words in the subject are a small signal on top. That's why the tool says so under every result: no filter blocks a single word on its own.
Tips for subject lines that get opened
- Put the reason to open first. The first 38 characters do the work on a phone. Lead with the noun and the news: "Your March invoice is ready to download" scores 100, but the phone shows "Your March invoice is ready to downloa…" and you still know what it is.
- Spend your emphasis once. One emoji, one exclamation mark, or one capitalised word can lift a line. All three at once reads like an ad, and the checks add up the same way a reader does.
- Write it like a person would. "Doors open Monday at 9am" scores 90 and sounds like a friend telling you something. Its only cost is a short-line warning.
- Test two versions, not twenty. Once both lines are green, the tool has done its part. Picking between two good lines is a judgement call, or a job for an A/B test on a slice of your list.
Use merge tags with care. A personalised line looks great with "Alex" and odd with a blank or "Customer" when a contact has no first name. Check what your sending tool puts in the gap before you lean on {{first_name}}.
Related email and writing tools
The Subject Line Analyzer grades a line you already wrote. If you're staring at a blank field, the Email Subject Line Tester reads your email body and writes five subject lines using different hooks. The Email Subject Generator gives you ideas from a short description instead. Paste the best of either back here and score it.
For the email itself, the Cold Email Generator writes a three-sentence outreach email. The Readability Checker tells you whether your body copy reads at the grade level your list expects. If you need an exact count for a preheader or another field with a hard limit, the Character Counter gives you the exact number. The Case Converter fixes a line someone typed in all capitals.
Frequently asked questions
Does a higher score mean a higher open rate?
Not directly. The score measures whether the line avoids the habits that hurt opens: too long, too loud, too spammy, too tricky. It can't measure whether your readers care about the topic. A Strong line about something nobody wants still gets ignored. Use the score to remove the obvious problems, then judge the message yourself.
Is my subject line saved or sent anywhere?
No. This subject line checker runs in your browser as you type. The line isn't uploaded, logged or stored, so unreleased product names and client details stay on your screen. Close the tab and it's gone.
Is there a limit on how many lines I can test?
No. Test one line or a hundred in a row, and nothing asks for an email address along the way. Each line can be up to 300 characters. Past that, the tool tells you no inbox will show that much and keeps your text so you can trim it.
Does it check the preheader text too?
No. The Subject Line Analyzer scores the subject line only. The preheader is the grey line many inboxes show after the subject, and it's worth writing on purpose. If you leave it empty, some apps fill it with the first words of your email, which is often "View in browser". Count it with the Character Counter and keep the important part early.
Why are some spam words fine in one line but not another?
Because the check counts hits, not words. One hit is a warning, since a single "free" in "Free shipping on every order this weekend" is normal retail language. Two or more hits fail, because that's when a line starts to read like a promotion to a filter and to a person. Repeats count too, so "free" three times is three hits.
Should I trust this or run an A/B test?
Both, for different jobs. This subject line tester catches problems before you send, in seconds and to nobody. An A/B test tells you which of two decent lines your own readers prefer, but only after the send and only on a list big enough to show a real difference. Score first, then test the two lines that survive.