MarketingSandbox · bring your own key

Test “Email Subject” with your own key

Paste an Anthropic, OpenAI, or OpenRouter key. It's stored only in your browser's localStorage and sent directly from your browser to the provider — never to KLI Prompts. We have no backend that can see it.

How this works (honestly)

  • Your key lives in localStorage on this device only.
  • The HTTP request to the LLM goes from your browser straight to api.anthropic.com / api.openai.com / openrouter.ai.
  • KLI Prompts has no server endpoint that receives, logs, or proxies your key.
  • Clear it any time — there's a button below.

Step 1 · Provider

Recommended for this prompt: any · temperature 0.4

Step 2 · Your API key

Saved to localStorage on this device. Never sent to KLI servers.

Step 3 · Fill the variables

Final prompt (sent to anthropic)

You are an expert email copywriter specializing in high-converting subject lines.

Generate exactly {{params}} email subject line variants for the following campaign:

Email Purpose: {{params}}
Target Audience: {{params}}
Email Type: {{params}}
Tone: {{params}}
{{product_line}}
Requirements:
- Each subject line should be compelling and optimized for open rates
- Vary the approach across variants (e.g., curiosity, benefit-led, urgency, social proof, personalization)
- Keep subject lines concise (under 60 characters when possible)
- Make them feel authentic and not spammy
- Tailor them to the specified tone and audience

Return ONLY a JSON array of strings — the subject lines — with no additional text, explanation, or formatting. Example format:
["Subject line 1", "Subject line 2", "Subject line 3"]

Output — will stream here

Nothing yet. Fill in variables and click Run.

Prompt slug: email-subject

Prefer copy-paste? Back to the prompt page →