Simplify
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.
iPhone & Android · your own API key
A book that rewrites the passage you are reading.
MetaBook interviews you about a topic, proposes a chapter outline you can edit, and writes the chapters on demand. Then — the point of the whole thing — you hold any passage while reading and say simplify this. The book changes in place, and every byte you did not point at stays exactly as it was.
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
The hard part was never the writing.
A model will write you a book about anything today. That is not what stops people. What stops them is what happens the moment a paragraph is too dense.
What it takes now
- Ask a chatbot for a chapter.
- Convert the answer to EPUB by hand.
- Get the file onto the phone.
- Read it in a separate e-reader.
- Hit a passage that is too dense.
- Copy it, switch apps, paste it, ask.
- Get a new chapter — start again at 2.
Every fix costs an app switch and a file conversion, so you stop asking for fixes — or you stop reading.
What it takes here
- Say what you want a book about.
- Answer a few questions.
- Read.
- Hold a passage and say what is wrong with it.
Step four is the product. Everything else exists so that step four has a book to happen in.
Four actions
Hold a passage. Say what is wrong with it.
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.
Expand
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.
Example
Adds a worked example to the passage. Short, concrete, and written into the book where the abstraction was.
Ask
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
“The book changes in place” is a claim.
Here is what backs it.
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.
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The version is checked before the call, and again before the write.
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.
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The request carries the passage and its neighbours. Never the chapter.
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.
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The reply is spliced by the app, not by the model.
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.
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Then the chapter is re-read and compared, block by block.
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.
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Undo does not rewind.
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.
Making a book
A topic, a short interview, and an outline you own.
The other half of the app. 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.
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1
The topic, and the language
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.
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2
Three to eight questions
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.
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3
An outline you can edit
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.
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4
Chapters, one at a time, on demand
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.
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5
The book remembers itself
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.
Money
You are spending your own money, so the app never hides it.
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.
- An estimate before, a figure after. Anything that spends says what it will cost before it runs, and what it actually cost when it is done.
- A daily cap and a per-book budget, on by default. They refuse. There is no “continue anyway” button — raising a limit is a decision you make in Settings, deliberately, not one you make mid-flow with a chapter half-written.
- Every call writes a row, successful or not. The ledger is on your device and it is yours to read: what the call was for, which model, what it cost.
- Prices come from the provider's live feed, and amounts are stored as whole numbers of a billionth of a dollar. Nothing is rounded into existence.
- One model choice runs everything, with a recommended pairing as the default — a fast model for the reading loop, a stronger one for writing chapters. Per-task pickers are there if you want them.
Your key, your provider, your device
There is no backend. Not a small one — none.
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:
Your text goes to your provider, and nowhere else
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.
The key lives in the phone's secure storage
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.
Two ways in, and they are peers
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.
The library is a file on your phone
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
The parts that make it a reader, not a demo.
Ten languages
English, German, Spanish, French, Italian, Portuguese, Russian, Turkish, Indonesian and Vietnamese — for the app, and separately for each book.
Export, losslessly
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.
Listen to a chapter
The system voice, sentence by sentence, with the phone's own play controls on the lock screen.
Mathematics, typeset
Display and inline formulae are part of what a chapter may contain — and they are drawn, not printed as dollar signs and backslashes.
Every version kept
Each chapter keeps its history: what changed, which model changed it, what it cost, and what the instruction was.
Paper and night
A reading theme that is designed rather than inverted, with the app around it built from the same palette.
Nothing is lost to a kill
Text is written down as it arrives. Force-quit the app mid-chapter and you come back to everything you had already paid for.
The same on both phones
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
What it does not do.
- It needs an API key. MetaBook has no server and sells you nothing, which means it cannot pay for your generation. You bring an OpenRouter account — connecting one takes a couple of taps — and the bill is yours. Without a key you can look around, but nothing is written.
- The chapters are written by a language model, and checked by nobody. A model states wrong things as confidently as right ones. A book here is a good starting point and a bad citation.
- No fiction. This is for non-fiction and for learning. Novels are a different job and it does not do that job.
- Phones only. Android and iOS. There is no web version and no desktop one.
- No accounts, so no sync. Your library lives on one device. Moving it to another is a backup file you carry across yourself.
Read something written for you.
Then change it.
Free to install. What you spend is what your provider charges, and the app tells you before you spend it.