How do page-locked recaps work?

01The pipeline in one picture

Every page-locked tool has to solve the same four problems in order: where are you, which text is that, what is the AI allowed to see, and what should it write. The sections below take them one at a time.

02Step 1: How does the app find your place?

There are four common ways, and they differ in precision:

1. Your ebook position. Inside an ebook app, the app already knows your position. Kindle's Story So Far uses this: Amazon describes "a catch-up tailored to your current position in the story".
2. A photo of the page. The app reads the text in the photo and looks for it in the book. Because it matches words rather than a page number, it can work across editions. Magic Bookmark says this works with "any edition, paperback or hardcover".
3. A typed page number. Quick, but page numbers differ between editions, so the app has to know which edition you mean or accept some imprecision.
4. The last phrase you heard. For audiobooks there is no page, so the app matches a phrase to the text. Magic Bookmark added this in October 2026 and calls it CatchPhrase.

Chapter-based apps such as Thus Far take a simpler route: you photograph the page, scan the barcode or tap the chapter, and the app stores which chapter you are in.

03Step 2: How does it match your place to the book's text?

To stop at your page, the system needs a version of the book's content it can line up with your place. That is the main reason these tools cover "supported titles" rather than every book:

• Kindle works inside ebooks it already sells or lends. According to the Authors Guild's account of what Amazon told it, Ask this Book's responses are "based solely on the text of the book purchased by the user".
• Magic Bookmark works alongside your own copy and covers a catalog of supported titles. Its page for authors says it launched with "several hundred" books and that adding each one is "a pretty intensive process".

Neither maker publishes exactly how its content is prepared, so we do not guess beyond what they say.

04Step 3: What does "cut off at your page" mean?

This is the step that makes a tool page-locked. Before the AI writes anything, the system limits the material it can draw on to the part of the book before your place. Text after your page is simply not part of what it is given.

What the makers say about this step:

• Magic Bookmark: "Magic Bookmark only knows the story up to your exact page and cannot see ahead. Recaps, the cast, and chat all stop where your bookmark sits."
• Kindle Ask this Book: "All responses provide immediate, contextual information up to your current reading position", with the option to "ask questions about the entire book".
• Kindle Story So Far: "spoiler-free refreshers up to where you've read".

Compare that with a general chatbot. When you ask ChatGPT to "only cover up to chapter 12", the whole book (and reviews, and wiki pages) may still be part of what it knows. Your request is an instruction, not a cut-off.

05Step 4: How is the recap written?

A language model writes the recap, the cast list or the answer from the material it is allowed to use. The Authors Guild wrote that Amazon's description of Ask this Book "may suggest" retrieval augmented generation, or RAG, while noting it had no confirmation. In plain terms, RAG means the system first retrieves relevant passages and then asks the model to write from them. Applied to a page lock, the retrieval step only reaches back from your place.

Cast lists follow the same rule. Magic Bookmark's website says its cast list is "built only from what you've actually read", that "New characters appear only once you've met them", and that "Nothing from later chapters leaks into a description."

06What can still go wrong?

A page lock removes one big risk, the model using later pages. It does not remove the others:

• The wrong place. A blurry photo, a different edition or a mistyped page can put the bookmark in the wrong spot. If the recap mentions something you do not remember reading, check your bookmark first.
• Wrong details. The model can still misstate what happened in the pages it was given. AI makers call this hallucination. See How to check an AI recap.
• The edge of a page. If you are halfway down a page, a page lock may include the rest of it.
• Choosing a wider scope. Ask this Book's whole-book option is a deliberate choice that removes the lock for that question.
• Earlier books in a series. A recap of book three may draw on books one and two. That is usually what you want, but it is worth knowing.

07How can you tell whether a tool is page-locked?

Ask four questions of any reading tool:

1. Does it ask where you are (page, position, phrase) before it answers?
2. Does the maker say it stops at your page or position, not just at a chapter?
3. Does it work only for supported titles? (A tool that claims every book usually relies on general knowledge.)
4. Is there a whole-book or "spoilers on" option, and is it off by default?

Our AI reading companion checklist turns these into a printable list.

08Which tools use which kind of lock?

Details for each are in the comparison table.