Quick answer. Set a system prompt with the voice you want and it applies to every reply. "Be concise and direct" or "Be warm and reassuring" works across Claude, ChatGPT, Gemini and Copilot. For deeper context, see the system prompt guide.
Ready-to-use tone templates
| Voice | System prompt |
|---|---|
| Formal | "Use professional, formal British English. No contractions, slang or emoji." |
| Warm | "Be warm and encouraging. Acknowledge the person before answering, and keep a supportive tone." |
| Concise | "Answer in three sentences or fewer. Lead with the answer. No preamble." |
| Empathetic | "Respond with empathy. Validate the concern first, then give clear guidance." |
| Direct | "Be blunt and direct. State the answer plainly, skip hedging and caveats." |
| Technical | "Write for an expert audience. Use precise terminology and assume domain knowledge." |
| Friendly-casual | "Be friendly and conversational, like a helpful colleague. Plain language, no jargon." |
Where to put it
- ChatGPT: Custom Instructions, or a Project/Custom GPT system prompt.
- Claude: Projects custom instructions, or the system parameter via the API.
- Gemini: Gem instructions, or system instruction via the API.
- Copilot: agent/declarative settings where available; otherwise lead each chat with the instruction.
- Any API: the dedicated
systemrole — the most reliable place of all.
Tips that make tone stick
- Set it at the system level, not buried mid-conversation — system instructions persist.
- Be specific. "Professional" is vague; "formal British English, no contractions" is followed precisely.
- Show, don't just tell. One short example of the desired voice anchors it strongly.
- Combine sparingly. "Warm but concise" is fine; five competing adjectives muddy the result.
Match tone to the job
Different contexts need different voices — healthcare leans empathetic, legal leans formal, internal tools lean concise. The customer service tone guide maps voice to industry, and the personality comparison shows each model's natural starting point.
Deploying a customer-facing agent? Pair tone control with the right base model via the customer service guide.