Education & Learning

Kern

Stop forgetting what you read.

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An iOS app that turns books you've finished into flashcards and uses spaced repetition to help you retain what you read.

The story

Screenshot of the Kern homepage — The Kern homepage

CROATIA — Kern is an iOS app for people who finish books and want to remember them. You type the title of any book you've read—whether paper, Kindle, library copy or audiobook—and Kern generates a deck of flashcards covering its key ideas, examples and surprising claims, written in Kern's own words rather than as excerpts. Spaced repetition brings the ideas back as they start to fade, typically in about five minutes a day, with cards from all your books interleaved in one feed. Books live on the Wall, staying inked while you review them and fading when you don't. Version 1.5 adds Home Screen and Lock Screen widgets so you can answer cards without opening the app, and optional reminders at a quiet time you choose. There are no streaks, no leaderboards and no account required.

Product features

Flashcards generated from book titles without highlights or uploads
Spaced repetition across all books in one interleaved feed
Four card types: quick check, fill the blank, explain simply, myth buster
Home Screen widget for answering cards without opening the app
Wall widget showing how fresh each book is
Lock Screen widgets showing which book is fading next
Reminders at your chosen quiet time, only on days you haven't reviewed
No account required, reviews work fully offline
Works with paper books, Kindle, audiobooks and library copies
Cards written in Kern's own words, not excerpts from books

Pricing

Pricing model: Freemium

First book free. Kern Plus subscription (monthly or yearly) unlocks unlimited books, or single-book one-time purchases available.

Kern metrics

Test results for kern.cards: Ahrefs Domain Rating and Majestic link data, with the change since the last test run.

Domain Rating: 14; +1 (up) since last check
Trust Flow: 3; no change since last check
Citation Flow: 21; no change since last check
Referring domains: 23; no change since last check
External backlinks: 76; no change since last check

Ahrefs Domain Rating tested 28 Oct 2026, retested with a change 26 Oct 2026. Product topic: Computers/Software/Operating Systems (3). Majestic tested 25 Oct 2026, retested with a change 25 Oct 2026. Majestic tests the link data. Trust Flow, Citation Flow and Topical Trust Flow are trademarks of Majestic-12 Ltd.

Kern domain specs

Show the domain specs

Source: the public RDAP record, checked 28 Oct 2026, 21:14 UTC.

Domain age: 4 months
Registered: 15 Jun 2026
Expires: 15 Jun 2027
Registrar: Cloudflare, Inc
DNSSEC: Not signed

Full domain specs: kern.cards

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Questions and answers

How do you remember what you read?

The most reliable way is active recall plus spaced repetition: test yourself on a book's key ideas at growing intervals instead of re-reading or highlighting. Kern turns a book you finished into recall cards and brings them back shortly before you'd forget them.

Why do I forget books a few weeks after finishing them?

Because of the forgetting curve: memory for new information decays exponentially, and most of a book is gone within weeks unless it's retrieved. Reading something once lets you recognize it later, but usually not recall it. Spaced review interrupts the curve and moves ideas into long-term memory.

Does spaced repetition work for books?

Yes. Spaced repetition is one of the best-tested findings in learning research, and it works for the ideas in a book as well as it does for vocabulary. Kern makes flashcards from the title and schedules the reviews, so ideas come back as they start to slip.

How do I make flashcards from a book without highlights or notes?

You don't need highlights. Type the title and Kern builds a deck of original cards from the book's key ideas, examples and surprising claims. The cards are written in Kern's own words rather than quoted, and they're ready in a few seconds.

Does Kern have Home Screen and Lock Screen widgets?

Yes. The Card widget (medium and large) puts a card from your books on your Home Screen and lets you tap an answer without opening the app. The Wall widget (small, medium and large) shows how fresh each book is, with faded ones first. Lock Screen widgets show the next book to fade and how many books are still inked. Kern requires iOS 17 or later.

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