bookmoth — AI that writes in your voice, not its own

“Every AI writing tool I tried produced text that sounded like AI. Competent, clean, utterly lifeless. I built bookmoth because I wanted a tool that could learn how I actually write, then stay inside those constraints on every sentence.”

Stu, founder

Four steps to a manuscript
that sounds like you

Brief. Voice. Plan. Draft.

Step 1

Build your brief

A guided conversation draws out your premise, characters, tone, and emotional arc. The richer this is, the better everything downstream becomes.

Step 2

Teach it your voice

Paste in your own prose. bookmoth analyses your sentence rhythms, dialogue patterns, and vocabulary at the mechanical level, then compiles it into a writing profile that governs every draft. Not just English: it works across major European and Asian languages too.

Step 3

Plan your chapters

Scene-by-scene breakdowns with beats, goals, and turns. Generate from your brief, build manually, or import an existing manuscript.

Step 4

Draft in your voice

Choose your model: Anthropic, OpenRouter, or a local LLM. Each chapter is governed by your brief and your writing profile. A 3,500-word chapter costs about 30 cents via Claude, less via OpenRouter. Edit, refine, run another pass. It's your manuscript.

Curious what bookmoth
sees in your writing?

Paste a few paragraphs. Get a free voice portrait by email. No account needed, no strings. Just an honest editorial read of your prose. Works in most major languages.

Get your voice portrait

See it work

From first conversation to first chapter

Write without distraction

Editorial feedback

Ask the Editor reads your chapter in the context of your entire manuscript, your brief, and your voice profile. Structural, tonal, and craft-level notes.

Sketch mode

Distilled voice profile for faster, cheaper exploratory drafts. Find the shape of a chapter in two minutes, then commit when you're ready.

Everything local

No account. No cloud. No analytics. Your manuscript, your brief, your writing profile: all stored on your machine.

Simple pricing

One fee. No subscription. Ever.

bookmoth

$49

one-time purchase

Full app for macOS and Windows
Free updates forever
Voice profile from your own prose
Chapter-by-chapter drafting
Sketch mode for fast exploration
Editorial feedback on demand
Import your existing manuscript
Everything stored locally

Get bookmoth

Bring your own API key (Anthropic or OpenRouter). A full novel typically costs $8–15 in API usage via Claude, less via OpenRouter. You control your spend.

How the costs work

You buy bookmoth once. Updates are free, forever. No tiers, no usage caps.

AI costs are between you and your API provider. A 3,500-word chapter costs about 30 cents via Claude. A full novel: roughly $8 to $15. Use OpenRouter or a local model and it costs less. You see exactly what you spend in your own dashboard.

Most AI writing subscriptions charge $19-29/month. In three months you've spent more than bookmoth costs forever.

Questions

Does it actually write in my voice?

This is the entire point. bookmoth analyses your prose at the sentence level and builds a writing profile from your actual patterns: your rhythms, your dialogue instincts, where you're lyrical and where you're blunt. That profile sits at the core of every chapter draft. The output won't be indistinguishable from what you'd write by hand, but it will be recognisably in your voice rather than the generic literary register most AI tools reach for by default.

What do I need to get started?

A Mac (macOS 10.15+) or Windows PC, and an Anthropic API key from console.anthropic.com. Takes two minutes to set up. No account, no subscription, no cloud storage.

How much does the AI cost to run?

A 3,500-word chapter costs about 30 cents via Claude, less via OpenRouter or a local model. A full novel typically costs $8–15 in API usage. Sketch mode is significantly cheaper for early exploration. You control your spend through your own API dashboard.

Will it write my whole book for me?

It writes full chapter drafts from your brief, your voice profile, and your plan. You steer the creative direction, edit, and refine. Think of it as a collaborator who sounds like you, not an autopilot.

Can I bring in an existing manuscript?

Yes. Import a .docx or .txt file with chapter markers. bookmoth reads what you've written, generates chapter summaries, and the editor picks up where you left off. Your existing prose becomes the foundation.

Is my work private?

Completely. Everything is stored locally on your machine. No bookmoth account, no cloud, no analytics. Text is sent to Anthropic via your own API key for generation only.

How is this different from Sudowrite?

Sudowrite treats AI as a co-writer with style options like "formal" or "casual." bookmoth reverse-engineers your actual voice from your own prose and enforces it structurally on every sentence. It's also a one-time $49 purchase, not a monthly subscription.

How does it compare to NovelCrafter?

NovelCrafter is strong on planning and structure. bookmoth goes deeper on the AI drafting side. The voice profile system, where the app analyses your prose and constrains every chapter to match your patterns, is something NovelCrafter does not do.

Can I use it for non-fiction?

Absolutely. Memoirs, narrative non-fiction, guidebooks, any long-form prose project. The voice system works the same way regardless of genre.

Can I write mature or explicit content?

Yes. bookmoth itself doesn't filter anything. How explicit the output actually is depends on the model you send it to. Claude (the default) will soften explicit scenes, that's Anthropic's product rather than ours. Uncensored models on OpenRouter, or local models via Ollama and LM Studio, will render whatever your brief calls for. Advanced Routing lets you mix: Claude for editorial feedback and light tasks, an uncensored model for the scenes that need it.

Does it work in languages other than English?

It does. The prose mechanics bookmoth analyses (sentence rhythm, repetition, specificity, interiority) work across languages. We've tested with Spanish, French, German, and Portuguese. The voice portrait and the app itself respond in the language you write in. If you try it in a language we haven't tested yet, we'd love to hear how it goes.

Windows?

Available in early access. Windows will show a SmartScreen prompt the first time you run it. This is normal for independently distributed software. Click More info, then Run anyway.

From the journal

Essays on writing, voice,
and finishing the book you started.

Essay · April 24, 2026 · 9 min read

How to find your writing voice (without faking it)

Voice is the most talked-about thing in writing advice and the least well defined. A practical guide for novelists who are tired of the clichés.

Read the essay →

See all essays

AI that writes in your voice,
not its own.

Same model. Same prompt.
Completely different prose.