How long should a subject line be?

Optimal length is 30-50 characters for mobile and up to 60 characters for desktop. The tool generates subject lines in both lengths so you can choose based on your audience. Over 60% of emails are opened on mobile, so short is generally better.

Do emojis work in subject lines?

Yes, studies show that emojis can increase open rates by 5-10% when used correctly. But overuse or irrelevant emojis can have the opposite effect. The tool suggests emojis that match the tone and content.

How do I avoid spam filters?

The tool automatically warns if the subject line contains common spam trigger words like "free", "click here", "limited offer" or excessive use of exclamation marks and capital letters. Follow the warnings to maximize delivery rates.

Can I A/B test the subject lines?

Yes, the tool generates 5-10 variants precisely for this purpose. Most email platforms (Mailchimp, Brevo, ActiveCampaign) support A/B testing of subject lines — send two variants to a small portion of the list and use the winner for the rest.

Contentscout

Emnefelt

What it does

Creates subject lines that increase open rates. Choose between curiosity-driven, value-based or urgency-based styles.

Your email never gets opened — because the subject line does not stand out in a crowded inbox

The average office worker receives over 120 emails daily. Most spend under 3 seconds deciding whether to open or delete an email — and that decision is based almost entirely on the subject line. A weak subject line means your content — no matter how good — never gets read. For many recipients the subject line is the only basis for opening the email.

Generic subject lines like "Newsletter week 12" or "Update from us" give open rates below 15% — far below the industry average of 20-25%
Too long subject lines get cut off on mobile — over 60% of emails are opened on mobile where only 30-40 characters are visible, so the rest of the subject line disappears
Wrong tone scares away — too salesy subject lines trigger spam filters, too boring ones get ignored, and too clickbait-like ones destroy trust when the content does not match
No systematic testing — most people send emails with the first subject line they think of without testing alternatives or analyzing what works

AI-generated subject lines that increase open rates — with multiple styles and A/B test variants

Email Subject generates subject lines that make recipients click. You describe the email content and choose a style — curiosity-driven, value-based, urgency-based or personal — and get 5-10 subject lines optimized for open rates. All subject lines are within optimal character length for both desktop and mobile.

Multiple styles: choose between curiosity-driven ("You will never guess what we found..."), value-based ("Save 3 hours this week with..."), urgency-based ("Last chance: ...") or personal ("Hi [name], this is for you")
Optimal length: all subject lines are optimized for mobile (under 40 characters) with a longer variant for desktop — so they work regardless of device
A/B test variants: get 5-10 variants so you can A/B test and find the subject line that gives the highest open rate for your audience
Spam filter check: the tool warns if a subject line contains words or patterns that often trigger spam filters — so your email actually reaches the inbox

Features

Style selector: choose between curiosity, value, urgency, personal, humor or provocation — each style has a different psychological approach to get the recipient to open
Emoji support: add relevant emojis to the subject line to increase visibility in the inbox — the tool suggests emojis that match the tone and content
Preview: see how the subject line looks in Gmail, Outlook and Apple Mail on both desktop and mobile — including truncation on small screens
Spam word warning: the tool highlights words and phrases like "free", "click here" and "limited offer" that can trigger spam filters and reduce delivery rates

How it works

Describe the content of your email — what is it about, who is the recipient, and what is the goal (open, click, reply)
Choose style (curiosity, value, urgency etc.) and any preferences for length, tone and emoji use
Get 5-10 subject line variants ready to use — choose the best for the main send and use another for A/B testing

Use cases

Email marketers sending newsletters who need subject lines that stand out in a crowded inbox and increase open rates from 15% to 25%+
Salespeople sending cold emails who need subject lines that make decision-makers open instead of delete — where the difference between 5% and 15% open rate is enormous
Event organizers sending invitations and reminders who need subject lines that create urgency and FOMO without being spammy

Why use Email Subject?

The subject line is the single most important factor for whether your email gets opened. You can have the best content in the world, but if the subject line does not capture attention, nobody sees it. Email Subject gives you professionally crafted subject lines in seconds instead of minutes of pondering.

With multiple variants per email you can systematically A/B test and over time build knowledge about what works for your audience. Some audiences respond best to curiosity, others to value, and some to urgency. The tool gives you all the variants so you can find your winning formula.

The spam filter check is a bonus that many overlook. Even the best subject line is worthless if the email ends up in spam. The tool helps you avoid common traps that trigger spam filters and ensures your message actually reaches the inbox.

FAQ

How long should a subject line be?: Optimal length is 30-50 characters for mobile and up to 60 characters for desktop. The tool generates subject lines in both lengths so you can choose based on your audience. Over 60% of emails are opened on mobile, so short is generally better.
Do emojis work in subject lines?: Yes, studies show that emojis can increase open rates by 5-10% when used correctly. But overuse or irrelevant emojis can have the opposite effect. The tool suggests emojis that match the tone and content.
How do I avoid spam filters?: The tool automatically warns if the subject line contains common spam trigger words like "free", "click here", "limited offer" or excessive use of exclamation marks and capital letters. Follow the warnings to maximize delivery rates.
Can I A/B test the subject lines?: Yes, the tool generates 5-10 variants precisely for this purpose. Most email platforms (Mailchimp, Brevo, ActiveCampaign) support A/B testing of subject lines — send two variants to a small portion of the list and use the winner for the rest.

Try Emnefelt free