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MyBook

free · no ads · your key, your texts

The book you were looking for, written at your level.

Tell it what you want to learn. MyBook works out how much you already know — with a two-minute quiz or a slider from 1 to 5 — asks a few questions to give the text the right shape, and writes a book or an interactive course made for you, with the AI you choose.

Download the APK How it works

Version 0.2.0 · 19.3 MB · Android 7 and later

How it works

  1. 1

    Pick a topic

    Anything at all: from night photography to Python for data analysis, from the Renaissance to personal finance. Then choose a book to read or a course with exercises and quizzes.

  2. 2

    Find your level

    Take the quiz — ten questions from easiest to hardest — or move the slider yourself from 1, beginner, to 5, professional. The level decides how technical the text will be.

  3. 3

    Give it shape

    The model asks a few questions made for that topic: why you want to learn it, what interests you most, which examples speak to you. You also pick the tone and the length.

  4. 4

    Review the outline and read

    It proposes an outline you can rename, reorder or regenerate. Then it writes, chapter after chapter, and you read while the text arrives.

One topic, five levels

The level is not a label: it changes the words, the examples and how much is taken for granted. Try the slider.

Why is the sky blue?

Sunlight looks white, but it holds all the colours of the rainbow. As it passes through the air, blue gets bounced around far more than the other colours. So it reaches your eyes from every part of the sky, and the sky looks blue.

White sunlight is a mix of colours, and each colour has its own wavelength: short for blue, long for red. The molecules in the air deflect short wavelengths much more. This is called scattering: blue light, scattered in every direction, fills the sky.

It is Rayleigh scattering. Nitrogen and oxygen molecules are far smaller than the wavelength of light, and they scatter it more strongly the shorter the wave: blue (around 450 nm) much more than red (around 700 nm). Violet would scatter even more, but the Sun emits less of it and our eyes are not very sensitive to it. At sunset the light crosses much more air, loses its blue on the way, and the reds remain.

For scatterers much smaller than λ, the Rayleigh cross-section scales as λ⁻⁴: between 450 and 700 nm, blue is scattered about 5.9 times more than red. The sky's spectrum is the solar spectrum weighted by λ⁻⁴ and by the optical depth along the line of sight; at sunset the longer optical path depletes the blue. Scattered light is also polarised, most strongly at 90° from the Sun — which is why a polarising filter darkens the sky.

In the dipole limit the per-molecule cross-section is σ(λ) = (8π/3)·k⁴·|α|², with k = 2π/λ, corrected for the dispersion of the refractive index and for the King factor (≈1.05 for air), which accounts for molecular anisotropy. The scattered spectrum rises towards short wavelengths, but the perceived hue comes from integrating it against the CIE colour-matching functions: the eye's low sensitivity below 450 nm shifts it from violet to blue. Radiative-transfer models add multiple scattering and Mie extinction by aerosols, which desaturates the sky towards the horizon.

What it does

A book or an interactive course

A book to read from start to finish, or short lessons with hands-on exercises and a quiz at the end of each one that marks the lesson as completed.

Simpler or more technical, even later

A chapter too easy or too hard? Rewrite it at another level, with a couple of lines of instructions if you like. The rest of the book stays as it is.

An outline you decide

Rename, move, remove or add chapters before a single line is written. If it doesn't convince you, ask for another proposal and say what to change.

With the AI you choose

Gemini with its free key, OpenRouter's free models, Mistral, Claude, ChatGPT, Grok or a model on your own computer. MyBook asks every one of them to say plainly when something is uncertain and never to invent sources or figures.

Yours, even outside the app

Books stay on your phone and export to Markdown, which opens in any editor and converts to PDF or EPUB.

13 languages

The app speaks your phone's language, and the book can be written in another one: you can learn Spanish by reading about cooking in Spanish.

Which AI writes

You choose. Each name takes you straight to the page where you create that service's key; you paste it into the app once.

Set up more than one, and when a service runs out of quota MyBook switches by itself to the next.

Your key, your texts

MyBook has no server of its own and sells nothing: it writes with your key, straight to the service you choose.

Support the project

MyBook is free and will stay free. If it taught you something, a coffee is the whole business model.

Donate with PayPal Releases and changelog

Questions

Why do I need an API key?

Because the texts are written by an AI model, and someone has to run it. Instead of a subscription or ads, MyBook uses your key: with a free one it costs nothing, with a paid service you pay it only for what you use, and nobody in between sees your texts. Creating one takes a minute: the links are in the list above.

How much does a book cost?

Nothing, with a free key or a model on your own computer, within the daily limits of the free plans. With a paid service it depends on the length and the model: with Claude's default model a medium book, eight chapters, usually costs a few dollars. Each project's details show the model, the tokens used and, where the price is known, an estimate at list prices.

Can I trust what it writes?

The large models are accurate on a great many subjects, and MyBook explicitly asks every one of them to say when something is uncertain and not to invent sources. Small free or local models make more mistakes. It is still AI-generated text: for medical, legal or financial decisions, always check with an authoritative source.

Why isn't it on the Play Store?

Because it doesn't need to be. The APK is signed with the same key on every release and published by an automated build, and the app checks for updates by itself, verifying the checksum before installing anything.

Is it safe to install an APK from outside the store?

Android will ask you once to allow installs from this source. The file comes from the public releases repository and its sha256 is published next to it in the manifest: you can check that the file you downloaded is the one that was built.

What happens if the free quota runs out?

If you have set up more than one service, MyBook switches by itself to the next one as soon as a service runs out of quota or credit — only before a chapter starts, so a chapter is never written by two different models. With a single service it tells you, and you can carry on the next day or choose another one.