Will your subject line make it to the inbox?

The sweet spot is 36–50 characters. That’s long enough to communicate something specific, short enough to display in full on most email clients. The critical threshold is 37 characters — anything longer gets cut off on many mobile devices. Put your most important words first so the message lands even if the end gets clipped.

One or two emojis used naturally are fine and can actually improve open rates by making your email stand out in a crowded inbox. More than two starts to look like spam and can trigger filters on some clients. The key is context: an emoji that reinforces your message is fine; a string of random symbols is a red flag.

75 or above is what you’re aiming for — that means no major red flags and a good chance of reaching the inbox. A score between 45 and 74 means there are some issues worth fixing before you send. Below 45 is high risk: your email is likely to be filtered as spam and we’d recommend a rewrite.

This tool checks your subject line for the patterns that spam filters flag most commonly. It’s a strong signal of deliverability risk, but it’s not a live spam filter test. Other factors affect deliverability too — your sender reputation, your domain authentication (SPF, DKIM, DMARC), and the quality of your list. For the full picture, see our guide to email deliverability.