iPhone & Android · your own API key
MetaBook interviews you about the topic — what you already know, what you want out of it, how deep to go — proposes a chapter outline you can rename, reorder and cut, and then writes the chapters on demand, one at a time, on your phone. And when a passage lands badly, you hold it and say simplify this.
No account. No server of ours. No analytics. Model calls go straight from your phone to your provider, billed to you — and every one of them says what it will cost before it runs.
The problem
A model will draft you a chapter about anything today. Turning that into a book you can sit down and read — on the right topic, at the right depth, in something that behaves like a reader — is the part nobody has done.
What it takes now
Every step costs a file conversion or an app switch, so you stop asking for the book you wanted and read the one that exists.
What it takes here
One to three are the book, and they are most of the app. Four is what you do to it without ever leaving the page.
First · making a book
The half of the app you use first, and the one that decides whether the book is worth reading at all. It stops before any chapter has text, so you see the shape of the book — and what it will cost — before a chapter is paid for.
The language a book is written in is chosen here, before the first call, and never again. It is what the interview asks in, what the outline comes back in, and what every chapter is written in. Ten to choose from.
What you already know, what you want out of it, how deep to go. You end the interview, from the third question on — a model that announced it had heard enough would be deciding how much more of your money to spend.
Rename, reorder, insert, remove. Editing the outline costs nothing and calls nothing — it moves titles and synopses, never text. A chapter you have not written yet says so, with its synopsis, instead of showing you a blank page.
A chapter takes minutes and arrives as it is written. Leave the app and it keeps going — the request is handed to the phone itself, and a notification says when the chapter is ready. Come back to an interrupted one and it continues from what you already paid for rather than starting again.
Two documents: a seed taken from your brief that no model ever rewrites, and a rolling summary refreshed as chapters are absorbed. It is why chapter nine still knows who it is written for, and does not explain chapter two again.
Nothing here is written until you ask for it, and nothing you have already paid for is thrown away. Text is saved as it arrives, so a force-quit mid-chapter costs you nothing but the rest of the chapter.
Then · while reading
The book is written for you, but no brief survives contact with a paragraph that is too dense. So the second half of the app is one gesture: touch and hold any paragraph and a toolbar appears — the app draws it itself, so it is the same four actions on both phones. Three of them change the book. One deliberately does not.
Rewrites the passage in plainer words. You run this while reading, so it is the call the whole app is tuned for: the cheapest one it makes, and the fastest.
Rewrites the passage at greater length. Of the four it produces the most new text — for the paragraph that went past something you wanted more of.
Adds a worked example to the passage. Short, concrete, and written into the book where the abstraction was.
Answers a question about the passage — and the answer is never written into the book. Asking is not editing, and one action for both would make the book unsafe to ask about.
Select more than about a third of a chapter, or use Rewrite this chapter with nothing selected, and you leave this path for a whole-chapter rewrite — roughly fifty times the cost, stated and confirmed before it runs.
In place
Rewriting a passage inside a document you are holding open is the part everyone else solves by putting the answer in a side panel. Five decisions make it safe to put it in the book instead.
Offsets are computed against a particular version of a chapter. Slicing against text that has since moved would spend your money on a passage that is no longer there.
Two bounded slices around your selection, each snapped to a block boundary, so no request hands a model half of anything. It is what makes the call cheap enough to run casually.
What comes back replaces exactly the range you selected, and nothing else. The model is never in a position to touch a byte outside it.
Identical bytes outside the range is necessary and not sufficient: an unterminated code fence inside the replacement changes how the rest of the chapter reads without altering a byte of it. So the comparison is of the parsed document, not of the text.
It restores the previous text as a new version. History that ran backwards could not say what the model did, and every passage you had already selected would become ambiguous.
Nothing in the app retries a model call — a retry spends your money on the app's problem. The one thing that retries is the write.
Money
There is no subscription and nothing to buy from us. Every call is billed to the provider account your key belongs to, and the app is built as though you were watching the meter — because you are.
Your key, your provider, your device
No API service, no database server, no accounts, no hosting of any kind. The app on your phone talks to your model provider directly, and to nothing else. That is a decision with a cost, and it buys you this:
What you type and what your books hold leave the device only as part of a model call, addressed to the provider your key belongs to. There is no account to make, no server of ours in the path, and no analytics anywhere in the app.
Keychain on iOS, Keystore on Android, and nowhere else in the app. It never reaches a log, an export, or a backup — so a backup file you hand to somebody cannot carry your key with it.
Connect an OpenRouter account and approve it in the browser, or paste a key you already have. Both take you to the same place. You can also finish setup with no key at all and look around first.
One SQLite database — every book, every version of every chapter, the outline, the memory, the ledger. Back it up whole, restore it on the other phone, or delete all of it, key included, in one action that says exactly what it removes.
And the rest of it
English, German, Spanish, French, Italian, Portuguese, Russian, Turkish, Indonesian and Vietnamese — for the app, and separately for each book.
Markdown that contains each chapter's stored source byte for byte, EPUB 3 for an e-reader, and FB2. Exporting spends nothing and changes nothing.
The system voice, sentence by sentence, with the phone's own play controls on the lock screen.
Display and inline formulae are part of what a chapter may contain — and they are drawn, not printed as dollar signs and backslashes.
Each chapter keeps its history: what changed, which model changed it, what it cost, and what the instruction was.
A reading theme that is designed rather than inverted, with the app around it built from the same palette.
Text is written down as it arrives. Force-quit the app mid-chapter and you come back to everything you had already paid for.
One codebase, and a rule that a feature exists on both targets or on neither. The selection toolbar is the app's own, so it behaves identically on each.
Before you download it
Free to install. What you spend is what your provider charges, and the app tells you before you spend it.