Free tool · No signup · Runs in your browser
Grade any cold email subject line - live.
Type a subject line and get an instant grade from A+ to F based on spam-trigger words, ideal length, sentence case, personalization tokens, and benchmark open rates. Everything runs in your browser - we never see your subject lines.
0 / 55 ideal
Try an example:
Length
Targets 35–55 chars - the open-rate sweet spot across 4.1M sends.
Spam triggers
Flags 21 high-risk phrases from ISP spam filters.
Tone
Detects ALL-CAPS, exclamation marks, and marketing-speak.
Personalization
Credits tokens like {{first_name}} that lift opens ~18%.
Run it at scale
A/B test subject lines across thousands of sends.
Prospea auto-picks the winning subject mid-campaign, so you compound open rate over the send - not across 12 manual tests.
Start free - 20 leads / month