$99once
One payment. Every update, forever. Bring your own key and keep hold of your words. Nothing recurring.
Own bookmothSlow writing. Finished books.
bookmoth helps you finish the book you want to write, in a voice you recognise as your own.
It learns from your prose, keeps track of your story, and helps you plan, write and revise. AI drafting is there when you ask for it.
You decide what belongs on the page.
macOSWindows
$99, once. The voice tool is free and needs no account.
The story
Behind every
book, a writer.
Your voice is already there, in whatever you've written. bookmoth reads it and holds on to it, so any help you take still sounds like you.
See what your voice looks like →
Write the
book.
The app
One app.
Your whole book.
Manuscript, plan, voice, Codex and editor share one project, so nothing needs explaining twice, and no change reaches the page without your say-so.
- StartA blank page, a brief built with the editor, or a manuscript you already have. Import it and carry on.
- WorkWrite without clutter, or think it through with an editor who has read the whole book.
- FinishWord, Markdown, plain text or a typeset PDF. Yours to take anywhere.
The real application, shown at its original proportions. Chapter 3 of a 69,204-word manuscript.
Try your voice
Same model.
Same prompt.
Different writer.
A writing profile turns evidence from your prose into a standard every draft has to meet. Same model, same scene. The second one knows how its writer writes.
Free. No account. It reads your writing and tells you what it sees.
Try it on your own writingWhere we stand on AI
Agnostic about how.
Fussy about the book.
Yes, there is AI in bookmoth. It works for you, in your voice, and it never gets a credit. Use it for every paragraph or for none; the price is the same and the book is still yours.
We built voice as a constraint, not a setting. Before bookmoth drafts a line it has read thousands of your own words and written itself a style guide it is not allowed to break. That is the difference between a tool that writes for you and one that writes as you.
bookmoth keeps no copy of your book. No account, no server, no analytics. Your words go only to the model provider you chose, under your own key, or stay on your machine entirely.
Read the questions we get asked →As much help as you choose
You lead.
bookmoth follows.
Before, during or after the writing. Every tool starts with your decision to use it.
Your writing profile
bookmoth learns what makes your prose yours.
Load in writing you trust. bookmoth studies rhythm, dialogue, texture and habit, and turns the evidence into a constraint every draft and edit has to obey.
Try it on your own writing, free
Story Plan
Built for second thoughts.
Chapter by chapter, scene by scene. Reshape the structure, move a beat, try another direction. Earlier plans and drafts stay where you left them.
See the whole application
Automatic Codex
Nobody’s eyes change colour in chapter nine.
Characters, places, relationships and facts become proposed entries as you write. A fact knows which chapter made it true, so early chapters never learn late twists. You keep, edit or bin every one.
See the full Codex guide
Manuscript editor
An editor at your side, not in your way.
Discuss a scene, argue a structural choice, or hand over a selected passage with the manuscript, plan and Codex in context. Read the change, keep it or bin it, or carry on writing yourself.
See the whole applicationIncluded companion
Take bookmoth
with you.
Read, make notes and carry the manuscript on from iPhone or iPad. Changes come back to the desk through your own iCloud. Included with bookmoth.
Tap either device to enlarge.
Pay once.
Your models.
Your manuscript.
No account. No server. Your book stays on your computer, or in a cloud you chose.
Write the
book.
Bring your own key.Choose Anthropic, OpenRouter, Ollama or LM Studio.
Private by design.Cloud requests go only to the provider you select. Local models stay local.
macOS and Windows.The iPhone and iPad companion is included.
Before you ask
Questions,
answered plainly.
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 will not be indistinguishable from what you would write by hand, but it will be recognisably in your voice rather than the generic literary register most AI tools reach for by default.
The codex is bookmoth’s built-in reference for your world: characters, places, lore and items, with aliases, per-character voices, and relationships. It builds itself as you draft, scanning your chapters, proposing entries for your approval, and flagging contradictions before they become canon. You control exactly what the AI sees, per entry and even per detail.
The editor is a conversation that lives inside your manuscript and reads your live prose, your brief, your voice profile, the plan, and the codex entries that matter. Ask it to tighten a passage, raise the tension, or check continuity, highlight a sentence and have it edit just that selection, or have it reshape your chapter cards and scenes. Nothing reaches your manuscript without you approving a diff, and every change saves as a version you can roll back.
A Mac (macOS 10.15+) or Windows PC, and an API key from an AI provider. Most writers use Anthropic (Claude), where you create a key at console.anthropic.com, or OpenRouter, which gives you one key for many models at openrouter.ai/keys. You can also run a local model for free. It takes two minutes to set up, and the setup guide walks you through it. No bookmoth account, no cloud storage.
It depends on what you do and which model you use, because you pay your AI provider directly, not us. Drafting a chapter is the main cost, from a couple of cents on a budget model up to around 30 cents on Claude. Lighter jobs cost less each, but they add up over a long book, especially scanning chapters to build your codex. The fix is to mix models: keep Claude for the prose and point bulk jobs like codex scanning at a cheaper model, a smaller Claude, an OpenRouter budget option, or a free local one. You see every cent in your provider’s dashboard.
No. bookmoth is $99 once, and it's yours for good: free updates forever, no usage caps, nothing recurring. The only other cost is the AI usage you choose, billed by your provider rather than us.
Only as much as you want it to. Some writers lean on it lightly, using it to plan or to keep their codex straight, and write every word themselves. Others have it sketch out scenes or whole chapters to react to while they shape the book. Either way you stay in charge: it drafts scene by scene from your brief, your voice profile and your plan, and you steer, edit any scene or chapter, run another pass, or keep an earlier version.
Yes, and it is one of the best ways to start. Import a .docx or .txt manuscript and bookmoth reads the whole thing: it splits it into chapters, writes a summary of each, maps out your story plan, and scans the prose to build your codex of characters, places and lore, all for your review. It can also learn your writing profile from your own chapters, so anything it helps with sounds like you.
Completely. Everything is stored locally on your machine. No bookmoth account, no cloud, no analytics, no telemetry. Your prose is only ever sent to the AI provider you choose, under your own API key. bookmoth itself never sees your work, never stores it, and never trains on it.
No. Never. bookmoth doesn’t have a model of its own. Your prose goes to the AI provider you choose (Anthropic, OpenRouter, or a local LLM via Ollama or LM Studio), via your own API key. Anthropic doesn’t train on API traffic by default. Local models train on nothing. Your work stays yours.
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. And where Sudowrite is subscription-only, bookmoth is $99 once, and it’s yours.
NovelCrafter is strong on planning, but it makes you build the codex by hand, entry by entry. bookmoth builds your Codex for you: it scans your chapters, proposes characters, places and lore for your approval, keeps aliases and relationships straight, and flags contradictions before they become canon. On top of that, bookmoth reverse-engineers your own voice from your prose and holds it on every chapter, which NovelCrafter does not do. And it is not only for heavy-worldbuilding fantasy: the same system works for any genre, from literary and crime to romance and non-fiction. Unlike NovelCrafter’s subscription-only pricing, bookmoth can be owned outright: $99 once.
Absolutely. Memoirs, narrative non-fiction, guidebooks, any long-form prose project. The voice system works the same way regardless of genre.
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.
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.
Fully supported. The Windows build is the same app as the Mac version, with every feature and no limitations. The only difference is that Windows shows a SmartScreen prompt the first time you run it, which is normal for any independently distributed software. Click More info, then Run anyway, and you are in.