AI Prompt A/B Tester

Prompt A/B testing is the practice of comparing two or more prompt variants to see which produces better results. Instead of guessing, you systematically test different phrasings, structures, and levels of detail. This tool helps you compare prompts side by side on metrics like token count, clarity, and structure before sending them to an AI model.

By analyzing both prompts with the same heuristics, you can see which one has clearer instructions, better format specification, and more useful constraints. The diff highlight shows exactly which words differ between the two, helping you understand what changed.

Effective prompts often include: (1) A role or persona — "You are a..." or "Act as a..." — to set context. (2) Format specification — JSON, list, table, paragraph — so the model knows the output structure. (3) Examples — "For example..." or "e.g." — to illustrate the desired style or format. (4) Constraints — "Do not...", "Maximum 100 words" — to avoid unwanted behavior. This tool scores each prompt on these four dimensions and highlights which are present or missing.

Use A/B testing when you're iterating on a prompt and want to compare a short vs. long version, a vague vs. specific version, or a version with vs. without a role. The templates provide common scenarios to get started. Run both prompts through your actual AI model to see which produces better outputs — this tool gives you a structural comparison to inform your choice.