Email Subject Line Tester

Your subject line decides whether the email gets opened or ignored. Paste it in and this checks the length, spam-trigger words, emoji and tone — and shows how it'll look in the inbox.

Need more than the free basics? Testing the line is the easy part. To actually write, personalise and send the campaign — with AI that drafts from your brand voice and past sends — that's where a platform like ActiveCampaign earns its place.

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What makes a subject line work

Aim for roughly 30–50 characters so it isn't truncated on mobile. Lead with the value or curiosity, not hype. Avoid stacking exclamation marks, ALL CAPS and classic spam words (free, act now, 100%, $$$) — they hurt both deliverability and trust. A single relevant emoji can lift opens; three look like spam. The honest test: would you open it?

Frequently asked questions

How long should an email subject line be?

Around 30–50 characters is the sweet spot — long enough to be clear, short enough not to get cut off on mobile inboxes, which often truncate near 50 characters.

Do spam-trigger words really matter?

They contribute. Modern spam filters look at many signals, but words like 'free', 'act now' and '$$$', combined with lots of caps and exclamation marks, raise your risk of landing in spam.

Should I use emoji in subject lines?

One relevant emoji can boost opens and stand out in a crowded inbox. Several look spammy and can trigger filters. Test it with your own audience.

Does this tool send my subject line anywhere?

No — it runs entirely in your browser. To actually send and test campaigns at scale (A/B subject tests, AI drafting), you'd use an email platform like ActiveCampaign.

This tool is free and runs entirely in your browser. The link above is an affiliate link: we may earn a commission if you sign up, at no extra cost to you, and it never changes our honest take.