Most cold emails fail for the same five reasons: wrong length, a weak subject line, no real personalization, a vague or missing call-to-action, and language that reads as spammy hype. This tool scores your email against best-practice heuristics on all five dimensions, then walks through your actual sentences and tells you exactly which lines to fix and how.
Paste your subject line into the first field and your full email body (greeting through sign-off) into the second. The grade recalculates as you type. Read the "What to fix" list first — it explains why each sub-score landed where it did — then work through the rewrite table, which quotes your actual sentences and gives a specific fix for each one. Re-check the grade after editing; aim for 80+ before sending to real prospects.
This is one tool. Mastery is the whole picture. Get new sales skills resources the moment they land, and read the thinking behind The Mastery Standard.