{"id":"mkt2-subject-line-pair-one-variable","audience":"marketing","category":"brainstorming","track":"marketing","technique":"constraints","level":"beginner","title":"Write a subject line test pair that differs in only one thing","free":false,"task":"You're setting up an A/B test for the Fernhill Planner newsletter. Write a prompt for exactly three plain-text lines: \"A:\" with a subject of 7 words or fewer that contains the word tips, \"B:\" with a subject identical to A except that the number 3 is added at the very start (lowercase the old first letter if needed), and \"Changed:\" naming the single thing that differs. Neither subject may use an exclamation mark or the word free.","materialLabel":"Newsletter details (attached to your prompt automatically)","material":"FERNHILL PLANNER - November newsletter\n\nMain article: \"Plan your holiday week\": tips for scheduling family time, work deadlines and errands. The article has 3 tips (shown as a short list).\nAudience: busy parents who use the Fernhill Planner app.\nCurrent average open rate: 31%. Test goal: see whether a number in the subject helps opens.\nBrand voice: calm and friendly; no exclamation marks.\nThings the team tried before: \"Free holiday planning tips!\" (spam-filtered), \"You won't believe this planner trick\" (clickbait; unsubscribes rose).\nHow the tool works: we send A to half the list and B to the other half, then compare.\nLast test: A and B differed in both length and emoji, so we couldn't tell which caused the difference.","rules":[{"type":"plainText"},{"type":"maxWords","max":40}],"mistakes":[{"title":"Changing two things","why":"The AI rewrites B with a different tone and length.","fix":"Say: \"B is A with only the number 3 added at the start.\"","checks":["r1"]},{"title":"Using banned words","why":"The AI writes 'Free tips!'.","fix":"Say: \"No exclamation mark and no word free.\"","checks":["r2"]},{"title":"Missing labels","why":"The AI lists options with explanations.","fix":"Show the three labels: A:, B:, Changed:","checks":["r0"]},{"title":"Letting markdown through","why":"AI adds bold text and headings by default.","fix":"Add: \"Plain text only, no bold, no headings.\"","checks":["plainText"]},{"title":"Trusting the AI to count words","why":"AI is bad at counting and often runs past a word limit.","fix":"Cap each part (for example \"each line under 15 words\") so the total lands well under the limit.","checks":["maxWords"]}],"promptHints":[{"label":"Gives the three labels","patterns":["a:.*b:.*changed:"]},{"label":"Requires one difference","patterns":["identical","only one","single","one change"]},{"label":"Names the change","patterns":["number 3","the number"]},{"label":"Bans words and punctuation","patterns":["exclamation","free"]},{"label":"Caps length","patterns":["8 words","40 words"]}],"hint":"A test only teaches something if one thing changes. Give the labels, the exact change and the banned words.","mission":"Write two subject lines that differ by exactly one thing.","musts":["A has the word tips","B adds 3 at start","No exclamation or free"],"rubricLabels":["The output has exactly three lines starting A:, B: and Changed:, with A at 7 words or fewer containing the word tips","B is identical to A except that the number 3 is added at the very start (a lowercased first letter is fine), and Changed: names the number 3 as the single difference","Neither subject has an exclamation mark or the word free, and neither is clickbait"]}