What makes a cold subject line work
It is short enough to read on a phone, it is about the reader rather than about you, and it does not promise what the email cannot keep. Lower case and plain words often read as one-to-one; all caps, emojis and hype read as marketing.
A buying signal is the best opener there is: a new hire, a fresh round, a tool they just left. The Signal Detector finds them for one company; Coolie finds them every day.
Limits
5 answers a day per visitor, free and with no sign-up. Asking the same question again shows the same answer, and does not count. What you type is not kept: only the answer is, for 7 days.
Questions
How long should a cold email subject line be?
Short: a few words, under about 60 characters, so it is not cut on a phone.
Should I personalize the subject line?
When you have something true and specific, yes: their company, their role or a signal you saw. A first name alone adds little.
How should I test them?
Send two or three to similar people and compare replies, not opens: opens are no longer a reliable measure.
Is this tool really free?
5 answers a day per visitor, free and with no sign-up. Asking the same question again shows the same answer, and does not count. What you type is not kept: only the answer is, for 7 days.
Where Coolie comes in
These tools write from what you type. For the leads you pick, Coolie first researches the company and the person, then writes a personalized email and LinkedIn sequence from what it found: multichannel outbound.