The writing tool that will not write for you.
BranchBook breaks a book into layers and holds you to them. It checks that you did the work. It never suggests a word.
How it works
One sentence becomes a paragraph. That paragraph becomes several sentences. Each of those becomes a paragraph of its own. Keep going and the book is written — not from an outline you abandon, but from the outline itself.
A sentence
The whole book in one line. Subject, action, nothing else.
A paragraph
Expand that line to 150–300 words. The count is checked, not suggested.
Its sentences
Pick three to five sentences out of the paragraph. Each becomes a seed.
As far as you like
Every sentence expands, every paragraph divides. There is no floor.
What the reader will not do
There is an AI in BranchBook. Its job is to state the task, check whether you met it, and move you on. The list of things it is structurally unable to do is the reason the tool exists:
- Write a sentence of your book
- Suggest a plot, a character, a phrase, or a fix
- Rewrite, tighten, or improve anything you wrote
- Tell you what it thinks of the work
It answers in a fixed shape: pass or fail, one unmet criterion, one short sentence, and a quotation of your own words showing what the verdict is about. It has no channel through which prose could reach you, so this is not a promise about behaviour — it is a limit on what it can emit at all.
Your prose leaves this server once, to be checked. Submissions are sent to Anthropic's API for validation. Anthropic does not train its models on API inputs or outputs. Nothing you write is used to train anything, by us or by them, and we sell nothing to anyone. See the privacy policy.
Three ways to be done
They read alike and they are not the same, so the app says which is which the whole time you are looking at them.
| Action | What it does |
|---|---|
| Submit | Checks the count, then asks the reader whether the passage belongs to the one above it. Passing is what completes it. |
| Accept without checking | Completes it on your say-so. Recorded, and counted in your own statistics. |
| Declare finished | Closes a passage for good: nothing can be written beneath it. Reversible. |
What you keep
Your manuscript is yours. We claim no licence over it beyond what running the service requires, we do not publish it, and we do not train on it. Export the whole book to Word whenever you want, including while your subscription is lapsed — cancelling stops the writing, never the reading.
Price
- As many books as you want to write
- Unlimited passages, unlimited layers
- Word export, whenever, including after you cancel
- 14-day free trial, no card
- Cancel in one click, refund inside 14 days