Definition
A voice prompt is a 500-800 word reference document that captures how a specific person writes — sentence patterns, vocabulary, banned words, tone shifts, signature moves — fed into an AI tool before any task to produce output that sounds like that person rather than generic AI default.
Why voice prompts exist
Out of the box, every AI tool defaults to the same voice: polished, professional, characterless. Public reporting from LinkedIn editorial and platforms like BrightEdge consistently shows that AI-assisted content matches generic templates more than 70% of the time when no voice context is provided. The result is content that ranks the same as everyone else's, sounds like everyone else's, and converts at default rates.
A voice prompt is the structural fix. It does for AI what a brand voice document does for human writers — but more specific, because the AI needs mechanical rules, not vibes.
What goes inside a voice prompt
Five sections, in order:
- Voice essence. One paragraph describing how this person sounds. Not adjectives ("friendly, professional"). A real description: "Talks like a smart friend who's done this before. Direct, specific, slightly opinionated. Uses short sentences for emphasis and longer ones for explanation."
- Mechanical rules. Average sentence length range. Paragraph length. Contractions yes or no. Whether sentences can start with "And" or "But." Punctuation preferences. Lists vs. prose tendency. These are the patterns the AI can mechanically reproduce.
- Banned words. Phrases the person would never write. "Synergy." "Cutting-edge." "Thought leader." "Game-changing." Every voice has 10-30 of these. Without the list, the AI defaults to them.
- Tone by context. Email voice vs. LinkedIn voice vs. sales page voice. Same person, different rooms. Specify how the calibration shifts.
- Signature moves. The 3-5 habits that make the writing recognisably this person — contrast pairs, rhetorical questions, specific numbers instead of vague claims, particular sentence-opening patterns.
5 voice prompt examples (anonymised)
Example 1 — B2B founder (technical):
Voice essence: "Engineer who became a founder. Talks about marketing the way he used to talk about code: with concrete examples, named systems, and an aversion to abstraction."
Mechanical rules: 12-18 word sentences. 1-3 sentence paragraphs. Always uses contractions. Never uses semicolons. Always names the system before describing it.
Banned: "leverage," "ecosystem," "thought leader," "best-in-class," "deep dive."
Signature moves: Names a specific number in every post. Uses contrast pairs ("Not A. B."). Closes with a one-line provocation.
Example 2 — Coach (relational):
Voice essence: "Coach who reads like she's having coffee with the reader. Names the shame the reader is feeling. Then names what to do about it."
Mechanical rules: 8-15 word sentences. 1-2 sentence paragraphs. Heavy contraction use. Uses "you" 4x more than "we."
Banned: "elevate," "transform your life," "level up," "abundance," "high-vibe."
Signature moves: Always opens with the reader's pain. Always includes one specific scenario. Closes with a question, never a CTA.
Example 3 — Solo agency owner:
Voice essence: "Has been doing this 15 years. Has seen every version of the trend cycle. Refuses to play the latest game until the data justifies it."
Mechanical rules: 14-22 word sentences. 2-4 sentence paragraphs. Sparse contractions. Numbers in every paragraph.
Banned: "AI is the future," "next-gen," "the new way," "revolutionising," "in this economy."
Signature moves: Cites a specific year + claim. Uses "the actual numbers are" frequently. Skeptical reframe of trending topics.
Example 4 — Consultant (analytical):
Voice essence: "Reads like the person who'd ask why before agreeing with anything. Builds the case slowly, then lands the point hard."
Mechanical rules: 16-25 word sentences. 2-3 sentence paragraphs. Frequent en dashes. Frequent parentheticals.
Banned: "best practices," "low-hanging fruit," "alignment," "optimise," "north star."
Signature moves: Always lays out the assumption before the conclusion. Cites at least one source per post. Closes with the reframe.
Example 5 — Personal brand founder:
Voice essence: "Talks about her business the way she talks about her life. The unprofessional move IS the brand. Specific over polished. Honest over slick."
Mechanical rules: 6-12 word sentences. 1-sentence paragraphs allowed. Always uses contractions. Often starts with "Yeah" or "Look."
Banned: "delivering value," "passion project," "founder journey," "growth mindset," "intentional."
Signature moves: Specific dollar amounts. Specific dates. One-line reveals. The personal anecdote that lands the business point.
How to use a voice prompt across AI tools
ChatGPT. Three options. Paste into Custom Instructions (Settings → Personalization). Use as the first message of a fresh conversation. Or build a Custom GPT with the voice prompt in the instructions field — most reliable approach because it can't be forgotten mid-conversation.
Claude. Use Claude Projects: paste the voice prompt as the project's system prompt. Every conversation in the project inherits it. For one-off tasks outside a project, paste it as the first message.
Gemini. Use the Gems feature (custom assistants) and paste the voice prompt into the instructions. Works the same as Custom GPTs.
Other tools. The principle is universal: voice prompt first, task second. If the tool accepts a system prompt, the voice prompt goes there. If it doesn't, paste it before every task.
Voice prompt vs. custom GPT vs. fine-tuning
These three terms get confused. They're different layers.
- Voice prompt. The reference document. Plain text. Universal across tools.
- Custom GPT (or Claude Project, or Gemini Gem). A wrapper around a voice prompt that locks it in for a specific tool. Same voice prompt; different delivery mechanism.
- Fine-tuning. Actually training a model on writing samples. Expensive, requires technical work, only justified at very high volume. For solopreneurs: not necessary. A voice prompt + custom GPT covers 95% of use cases.
How to build your own voice prompt
The DIY workflow: gather 10-20 pieces of your existing writing, paste them into ChatGPT or Claude with the prompt "Analyse these samples and identify mechanical voice patterns: sentence length, vocabulary level, paragraph structure, recurring phrases, and what makes this voice distinct from generic professional writing." Edit the AI's analysis into the five-section structure above. Test it. Iterate.
Full step-by-step instructions: how to make ChatGPT sound like you. Free playbook: The Voice System Playbook.
When to pay vs. DIY
Pay (DFY) if: your hourly rate is over £100 and the 4-6 hour build is worth more in opportunity cost than the £497 service fee, or you've tried DIY and the output still doesn't sound like you. DFY Voice System uses The Voice Build methodology — same process documented in the playbook, executed for you in 2-3 working days. You own every asset.
DIY if: you have a focused weekend, want to understand the process before buying anything, or your writing samples are sparse and you'd rather develop the voice as you go.
Get a voice prompt built for you
DFY Voice System reverse-engineers your existing writing into a voice prompt + custom GPT + workflow. £497, delivered in 2-3 working days. You keep every asset forever.
See The Voice Build
Frequently Asked Questions
What is a voice prompt?
A voice prompt is a 500-800 word reference document that describes how a specific person writes — sentence patterns, vocabulary, banned words, signature moves, tone shifts by format. It's pasted into an AI tool before any task so the output sounds like that person rather than generic AI default.
How long is a voice prompt?
500 to 800 words. Shorter than 300 is too vague; longer than 1,000 eats into context window. The Voice Build methodology targets 500-700 words.
What goes inside a voice prompt?
Five sections: voice essence (one-paragraph description), mechanical rules (sentence length, paragraph length, contractions, punctuation), banned words (phrases never used), tone by context (how voice shifts by format), and signature moves (3-5 distinctive habits).
How do you use a voice prompt with ChatGPT?
Paste it into Custom Instructions, use it as the first message of every conversation, or build a Custom GPT with it in the instructions field. The Custom GPT route is most reliable because the voice can't be forgotten mid-conversation.
How is a voice prompt different from a brand voice document?
A brand voice document is for humans (style guide). A voice prompt is for AI (mechanical instruction set). The voice prompt is more specific and less abstract.
Can you make a voice prompt for free?
Yes. DIY takes 4-6 focused hours using existing writing samples. The Voice System Playbook documents the process for free. DFY costs £497-997 and saves the setup time.