Teach Claude how you write. Not how "a professional" writes. How you write.

AI writing tools are fluent. They're also generic. Ask five of them to write a pitch email and you'll get five versions of the same email — competent, forgettable, and nothing like you.

Voice Fingerprint fixes that. It reads your actual writing, identifies what makes it yours, interviews you about the choices you make on purpose, and produces a Voice Spec — a structured document that tells Claude exactly how to sound like you. Not a vague "tone: professional yet approachable." Concrete rules. Specific examples. A banned word list with reasons. The sentence rhythms you reach for. The clichés you've been quietly avoiding your entire career.

Then it gets better over time. Every correction ("I'd never say it that way") and every approval ("nailed it") feeds back into the spec. Your AI writing gets sharper the more you use it.

First use is automatic. Install the skill and open a new conversation — Claude detects that you don't have a Voice Spec yet and immediately launches the learning session without you having to ask. No special command needed.

It offers itself when you write. Once your spec is built, Claude recognizes when you're drafting something and asks: "I have your voice fingerprint on file. Want me to write this as you, not as generic Claude?" Say yes and it applies your spec. Say "always" and it stops asking.

Reads your writing. Upload 3-8 samples — blog posts, emails, pitch decks, social posts, memos, whatever. Diversity matters more than volume. A pitch email and a LinkedIn post reveal more about your range than eight blog posts.

Finds the patterns you don't notice. Sentence length distribution. Whether you lean Anglo-Saxon or Latinate. How you open a piece. How you close one. Whether you use em-dashes for drama or parenthetical asides for texture.

Finds what's missing. This is the part most style tools skip. Voice Fingerprint cross-references your vocabulary against common cliché pools — consulting jargon, marketing buzzwords, tech filler — and flags what's conspicuously absent. If you've written 10,000 words of marketing copy and never once typed "synergy," "leverage," or "game-changer," that's not an accident. That's your voice.

Interviews you. Samples can't reveal everything. The skill asks targeted questions: what words you deliberately avoid and why (the why catches adjacent bans you haven't thought of yet), British or American English conventions, where you want controlled randomness, how your voice shifts by audience, and what kind of writing makes you cringe.

Builds a Voice Spec. A structured document with your five non-negotiable signature traits, mechanical rules, audience modes, a tiered banned list, anti-patterns, and example rewrites showing the transformation from generic to you. Stored in Claude's memory so every future conversation inherits it.

Starts itself on first use. Install the skill and open a new conversation. If you don't have a Voice Spec yet, Claude immediately invites you to start the learning session — no special command needed.

Offers itself when you write. Once your spec exists, Claude recognizes when you're drafting something and asks if you want to write as yourself. Say "always" once and it applies your spec silently from then on.

Learns from corrections. Say "that doesn't sound like me" and the skill identifies what went wrong, generalizes the pattern, and proposes a spec update. Say "that's perfect" and the skill strengthens whatever rules produced the result. Changes batch up and push to your stored spec when they hit a threshold.

Download voice-fingerprint.skill from this repo. In Claude, go to Customize → Skills and upload the file.

Open a new conversation. You don't need to say anything special — the skill checks whether you have a Voice Spec, and if you don't, it immediately invites you to start the learning session.

If you'd prefer to trigger it manually, say:

"Learn my voice. I'm going to upload some writing samples."

Upload 3-8 samples. Mix formats — a blog post, an important email, a social post, a report. The more different they are, the better the skill maps your range.

Claude will show you what it found in your writing — patterns, tendencies, and conspicuous absences. It'll ask: "Here's what I'm hearing in your voice. Tell me where I'm right, where I'm wrong, and what I'm missing."

This is the calibration step. Push back where it's off.

Claude will ask about deliberate choices, localization preferences, where you want variance, and what makes you cringe. Answer honestly — the spec is only as good as the input.

Claude generates a Voice Spec and asks you to review it. Once you approve, it saves a compact version to memory (persistent across conversations) and gives you the full version as a downloadable file.

From now on, when you ask Claude to draft anything, it'll ask: "I have your voice fingerprint on file. Want me to write this as you?" Say yes to apply your spec. If you'd rather skip the ask and always use your voice, say "always use my voice fingerprint" — Claude will apply it silently from that point on.

When something's off, say so. "I'd never phrase it that way." "Too formal." "Lose the semicolons." Corrections accumulate and feed back into the spec. You can also say "update my voice spec" to trigger a manual revision.

The spec isn't a mood board. It's a constraint document with teeth:

• Five Signature Traits — ranked, non-negotiable. If Claude gets nothing else right, it gets these right.
• Structural Patterns — sentence length range, paragraph rhythm, opening and closing moves, transition habits.
• Vocabulary & Register — formality position, jargon policy, Latinate vs. Anglo-Saxon lean.
• Rhetorical Moves — argument structure, humor type and frequency, authority stance.
• Mechanics — English variant, Oxford comma, em-dash usage, quotation style.
• Audience Modes — how your voice shifts for different readers.
• Controlled Variance — where to introduce randomness and how much.
• Banned List — hard bans (never, with reasons), soft avoidances (only when earned), structural bans, and cliché families grouped by the reason they're banned.
• Anti-Patterns — what your voice is NOT. The mistakes a mimic would make.
• Example Rewrites — generic sentences rewritten in your voice, showing the before/after.
• Version History — every revision tracked with what changed and why.

Most style tools are set-and-forget. Voice Fingerprint is set-and-sharpen.

Corrections — When you edit Claude's output or say "that doesn't sound like me," the skill identifies the specific violation, generalizes the pattern, and classifies it: new rule, tighter existing rule, or a contradiction that needs resolving. It proposes the update, you confirm, it writes.

Approvals — When you say "perfect" or "nailed it," the skill identifies which rules produced the result and strengthens them. Rules that get praised three or more times get promoted toward the Signature Traits.

Batching — The skill doesn't update the spec after every correction. Changes accumulate until they hit a threshold (three corrections in the same dimension, a contradiction with an existing rule, or your explicit request). Then it shows you the diff and asks permission.

Versioning — Every revision gets a version number and a changelog entry. You can see exactly how your spec evolved.

• Ghostwrite without samples. The skill needs your writing to learn from. No samples, no spec.
• Replace your judgment. The spec is a starting point. You still approve, edit, and redirect.
• Work outside Claude. This is a Claude skill. It uses Claude's memory system and skill architecture.
• Copy another writer. It captures your voice. If you want to sound like someone else, that's a different tool.

• A Claude Pro, Team, or Enterprise account (skills require a paid plan)
• 3-8 writing samples (any format Claude can read — text, PDF, Word, pasted inline)
• 15-20 minutes for the initial interview

voice-fingerprint/
└── SKILL.md          # The complete skill — analysis, interview, spec
                      #   generation, memory storage, and learning loop

How long does the initial setup take? 15-20 minutes. The analysis is fast. The interview is where you spend time — and it's worth it.

Can I update my spec later? Yes. Say "update my voice spec" in any conversation. You can also upload new writing samples to extend it.

What if my voice changes over time? That's what the Learning Loop handles. As you correct and approve, the spec evolves with you.

Does it work for brand voices, not just personal voice? Yes. The same process works — just adjust the interview to focus on brand positioning and audience rather than personal preference.

What if I write differently for different audiences? The spec supports multiple Audience Modes. The interview asks about this specifically.

Can I see what's stored in memory? Yes. Ask Claude "what do you remember about my voice?" and it'll show you the stored spec.

Can I skip the "use your voice fingerprint?" offer? Yes. Say "always use my voice fingerprint" once and Claude will apply your spec silently on every writing task without asking. Say "stop using my voice fingerprint" to turn it off.

Can I delete the spec? Yes. Go to Settings → Memory and remove the Voice Spec entry, or ask Claude to forget it.

MIT. See LICENSE.

See CONTRIBUTING.md.

Built by Marcus Nelson — AI for Main Street.