Custom GPT System Prompt Builder — Full Persona Engineering

Most custom GPT system prompts are 2 sentences. The best ones are engineered like software — with edge case handling, tone calibration, output constraints, and persona consistency rules. This prompt builds a full system prompt for any assistant you want to create: - **Persona definition** — name, voice, expertise, personality - **Behavioral rules** — what it will and won't do - **Output format constraints** — how it structures every response - **Fallback behavior** — how it handles off-topic or ambiguous requests - **Anti-drift rules** — keeps the assistant on-task even after long conversations - **Few-shot examples** — shows the assistant what good looks like Works for: customer support bots, coding assistants, writing coaches, tutors, sales assistants, and more.