Enter your topic or offer and pick a campaign type, such as newsletter, sale, cold email or follow-up. You get 20 subject lines, each with a character count, length rating and spam-word warnings, plus a preview text checker and an inbox mock-up that shows what readers will see.
Last updated:
Subject lines
30–50 characters (ideal) under 30 or 51–60 over 60 (likely cut off). Click a line to preview it in an inbox.
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Subject line and checks
Chars
Copy
Inbox
Your Brand9:41 AM
Another sender8:15 AM
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How to use the Email Subject Line Generator
Choose the campaign type: newsletter, sale, cold email, follow-up, product launch, event or welcome.
Enter your topic and any extras: offer, brand or company, audience and deadline. More details unlock more templates.
Optionally add a merge tag for the first name and turn on emoji.
Press Generate 20 subject lines. Check the character count dot and the warnings on each line.
Click a line to see it in the inbox preview, write your preview text, then copy your favorites or download them as CSV for A/B testing.
How the subject line checks work
Each line is scored with simple, transparent rules:
Check
Rule
Why it matters
Length
Green 30–50 characters, yellow under 30 or 51–60, red over 60
Phones show roughly 30–45 characters in the inbox list; desktop clients show more
Can make the email look promotional or spammy to filters and readers
ALL CAPS
Any word of 4+ capital letters
Reads as shouting and is a classic spam signal
Punctuation
!!, ??, $$
Looks pushy and spammy
Emoji
More than one emoji
One can help in promotional mail; several look cluttered
Characters are counted as Unicode code points, and merge tags are counted as a typical first name (5 letters) so the length matches what readers see.
Subject line formulas by campaign
Campaign
Formula
Example
Newsletter
Benefit or curiosity + topic
The one thing about remote work nobody tells you
Sale
Offer + product + deadline
25% off summer sneakers ends Sunday
Cold email
Their company + your outcome, as a question
Can we help Acme Outdoors cut shipping costs?
Follow-up
Context + soft question
Any thoughts on the website proposal?
Launch
"Introducing" or "Meet" + product
Meet the Trailblazer backpack
Event
Invitation + event + date
Save the date: the Spring Growth Summit, May 14
Welcome
Warm greeting + brand or gift
You're in! Welcome to Dreamwell
Tips for better open rates
Front-load the important words: on phones the end of the subject is often hidden.
Make the sender name recognizable; readers look at it before the subject.
Be specific: numbers, names and dates beat vague hype.
Match the subject to the email: misleading subjects hurt trust and unsubscribe rates.
Test two versions on a small sample before sending to your whole list.
Frequently asked questions
How long should an email subject line be?
Around 30 to 50 characters is a safe target. Phones often show only about 30 to 45 characters of a subject in the inbox list, and desktop clients around 60 or more, so put the most important words first. The generator marks lines over 60 characters in red.
What words trigger spam filters in subject lines?
Phrases common in spam, such as free, act now, click here, guaranteed, 100%, cash, winner and urgent, along with ALL CAPS and repeated exclamation marks, can make an email look spammy to filters and readers. Modern filters weigh sender reputation and content as a whole, so one word rarely decides delivery, but it is wise to use them sparingly.
What is preview text and how long should it be?
Preview text (also called preheader) is the short line shown after or below the subject in most inboxes. Depending on the app and screen, roughly 35 to 140 characters are visible, so aim for about 40 to 100 and add new information instead of repeating the subject. If you leave it empty, the inbox shows the first text of your email.
Do personalized subject lines work better?
Adding the first name can make an email stand out, especially in cold and follow-up emails, but it works best when used occasionally and when your data is clean, so nobody receives "Hi FNAME". Test it against a version without personalization.
Should I use emoji in subject lines?
One relevant emoji can draw the eye in promotional and newsletter emails, but it may look out of place in business, cold or follow-up emails, and some emoji display differently across devices. The generator only adds them when you switch the option on.
How do I choose the best subject line?
Shortlist two or three lines that are clear, specific and within the ideal length, then A/B test them with a small part of your list and send the winner to the rest. Download the CSV to keep your test ideas in one place.
Is my content sent anywhere?
No. Subject lines are generated in your browser from built-in templates, and nothing you type is uploaded.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.