Subject Line Tester
Score an email subject.
Score an email subject.
How to use Subject Line Tester
- Type your email subject line into the field
- Watch the live score out of 100 update as you type
- Review flags for length, ALL-CAPS, spam words, and emoji
- Revise until length hits the 30-50 character sweet spot
About Subject Line Tester
Type an email subject line and watch it score out of 100 in real time. The tool checks character length against the 30-50 sweet spot and warns the moment a line runs too long for mobile inbox previews, which usually clip anything past about 30-40 characters on a phone. It counts words and emoji, flags ALL-CAPS shouting and runs of excessive punctuation, scans for common spam-trigger words, and checks whether you have added personalization like a merge tag or a direct address to the reader.
That makes it a quick spam checker and a readability check in one pass, useful whether you are writing a promotional blast, a B2B cold email, or a newsletter subject for an email marketing campaign. If you have been reaching for a branded checker like CoSchedule, Omnisend, or HubSpot, this covers the same core scoring without an account or a sign-up wall, and each deduction comes with a concrete tip so you know exactly what to tighten before you hit send.
Every check runs live in your browser with no limits, so you can test as many variations as you want and compare them side by side. Nothing you type is ever uploaded, sent to a server, or saved, which means you can paste real campaign subjects and client copy freely without worrying about where the text goes.
Frequently asked questions
- Is the email subject line tester free?
- Yes, it is completely free with no account, sign-up, or usage limits. Test as many subject lines as you like.
- Is my data uploaded or stored anywhere?
- No. The entire analysis runs in your browser using JavaScript. Your subject lines are never sent to a server, uploaded, or stored, so it is safe to paste real campaign copy.
- What is the ideal email subject line length?
- Aim for roughly 30-50 characters. That range stays fully visible in most inboxes and, importantly, in mobile previews that often cut off anything past about 30-40 characters. Longer lines up to 60 characters usually still work, but the end may be clipped on phones.
- How is the score out of 100 calculated?
- The tool starts at 100 and adjusts based on best practices: it deducts points for lines that are too long or too short, ALL-CAPS shouting, excessive punctuation, detected spam-trigger words, and emoji overload, and it adds points for personalization such as a merge tag or addressing the reader directly.
- Does it check my subject line for spam?
- Yes. It scans your line against a list of common spam-trigger words and symbol patterns and lists any matches inline, so you can rephrase them. It also flags ALL-CAPS and excessive punctuation, both of which spam filters tend to penalize.
- Which spam-trigger words does it detect?
- It checks against an inline list of common ones like 'free', 'buy now', 'guarantee', 'act now', 'click here', 'winner', '100% free', and symbol patterns like '$$$'. Any matches are listed inline so you can rephrase them. Avoiding these reduces the chance of landing in the spam folder.
- How will my subject line look on mobile?
- The tool warns you when a line is too long to fit a typical mobile inbox preview, which often shows only the first 30-40 characters. Front-load the important words so your message still reads clearly when the end gets clipped on a phone.
- Is this a free alternative to the CoSchedule, Omnisend, or HubSpot subject line testers?
- It scores the same core factors those tools check, such as length, spam words, and readability, with no account or email required. It is not affiliated with any of them, but it works well as a quick, private stand-in when you just need a fast score.
- Can I use it for B2B or cold emails?
- Yes. The same checks apply whether you are writing a B2B cold email, a sales follow-up, or a marketing newsletter. For B2B, keep the line specific and avoid promotional spam words, and use the personalization check to confirm you have referenced the recipient.
- Does it count words and emoji in my subject line?
- Yes, it counts both as you type. A short word count and one or zero emoji generally read cleaner, and the tool flags emoji overload so a subject does not look cluttered or trip spam filters.
- Does adding personalization improve the score?
- It can. The tool checks for personalization such as a merge tag or a direct address to the reader and adds points when it finds it, since personalized subjects tend to feel more relevant. Make sure any merge tag matches the field name your email platform actually uses.
- Does a high score guarantee my email gets opened?
- No. The score reflects widely used deliverability and readability best practices, but open rates depend on your sender reputation, audience, timing, and preview text too. Treat the score as a guide and always A/B test real subject lines with your own list.