FREE PRACTICAL AI LEARNING · LEARN BY DOINGNO SIGNUP NEEDED · YOUR WORK STAYS YOURS
Open PracticePRACTICAL AI ENGINEERING
FREE TOOL · WRITING

Write subject lines people actually open

Subject lines are tiny experiments. You will write ten variations using different angles — benefit, curiosity, number, question, urgency without lies — then check each one for mobile length and spam-style wording, and pick two to test.

⏱ 10–20 min · Works with or without AI · No signup

You will practise

  • Writing variations on purpose instead of at random
  • Keeping subject lines inside mobile preview length
  • Avoiding spam-filter and trust-killing wording

No AI key needed. The guided template works for everyone.

  1. 1Brief

    Specific answers make better results — with or without AI.

  2. 2Make

    Pick a route. The template gives you a structure with [[blanks]] to fill in yourself. Your own key drafts it for you — then you still check it.

    See the exact prompt — copy it into any AI chat you already use
  3. 3Check
    The same rules run on every draft, human or AI. Most first drafts fail something — that is the point.
      Self-check — judgement no checker can make
    • 4Improve
      Fix one item at a time, then check again. Notice which fixes made it better — that is the skill.
      1. Run the check first.
    • 5Ship
      Use it for real: send it, post it or save it. Record what happened — that is your evidence of learning.
    Pro moves
    Questions people ask
    What is the best subject line length?
    Many phones show roughly 30–50 characters, so front-load the key words and aim for under 50.
    How do I test subject lines?
    Send version A to a small random part of your list and version B to another, compare open or reply rates, then send the winner to the rest.
    Do I need an AI key to use this?
    No. The guided template teaches the same skill with no AI at all. If you add your own free key (Groq, Google Gemini, OpenRouter, Mistral or Cerebras), the tool can also draft and revise. The key stays in your browser and requests go straight to that provider.
    Where is my work saved?
    In this browser only (local storage), until you copy or download it. Nothing you type is sent to Open Practice.
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