Sponge & Stone turns any question into a branching rabbit hole. The facts you choose to keep become fact-checked flashcards, scheduled so you never lose them. Reading is the fun part. Remembering is now automatic.
Type anything and press enter to start a real rabbit hole, or pick a chip to watch the loop run in twenty seconds.
Cards are generated, not written by you : recall, reverse, comparisons, more. Each schedules on its own.
Three days later, this card comes back. Tap your answer.
Explore freely, keep deliberately, review a few minutes a day. Each success stretches the interval, from a day to a week to a season, until the knowledge sets in stone .
Start your first rabbit holeA real rabbit hole also streams live annotations, branch hooks, and rival theories. This is the pocket version.
Kindle notes, read-later queues, browser bookmarks: you save them and never look at them again.
Spaced repetition works; decades of evidence say so. But writing good cards is tedious enough that almost everyone quits before the compounding starts.
Chat explains things brilliantly, but it has no memory of what it explained and does nothing to help you keep it.
Sponge & Stone closes the loop between being curious and actually knowing .
You never fill out a form and you never write a card. You follow your curiosity, and structure happens behind the scenes. You just say yes to what's worth keeping.
Ask anything and get a short narrative with branching hooks, plus rival theories when scholars genuinely disagree.
Rabbit Holes, web clips, and Kindle imports suggest facts, never auto-save. You are the filter. One tap keeps it.
Kept facts become generated cards, scheduled by spaced repetition. Minutes a day; intervals stretch to seasons.
Built into every plan from day one.
The moment you keep a fact, it gets cross-referenced against web search and Wolfram Alpha, recording citations that support, correct, or add nuance . Wrong values get amended before you ever memorize them.
8,848 m → 8,848.86 m · amended in place, with the trail to prove it
Facts are stored as structured, unit-aware data : canonical SI values, superlatives, coordinates, precision-aware dates. Structure is why the system writes comparisons, map challenges, and word problems you never authored .
Get one wrong and it reads your answer, not just marks it: “You said 88 days. That's Mercury's orbital period.”
Scheduling runs on FSRS , the modern memory model fitted to hundreds of millions of real reviews, with leech detection that flags a card failing five times as badly written and offers to fix it.
Reviews are unlimited on every plan. Read the science →
A crack in mature stone patches fast. Recovery restarts at 10% of the old interval , not back at square one.
Every fact is a suggestion until you keep it. No auto-created noise clogging your review queue.
Full export in structured JSON or readable Markdown, every plan, any day, including the day you cancel.
Facts carry their citations, amendments, and check status. Disputed and controversial are honest states, not errors we hide.
Every rabbit hole runs real research on your behalf. Reviewing what you've kept, the part that makes knowledge stick, is unlimited on both.
We'll email you the day before your trial ends. Cancel anytime. Everything you've kept is yours to download as JSON or Markdown, even after you go.
We use AI where it earns its place: every rabbit hole and fact-check runs real research on your behalf, and that costs real money. Free tiers quietly pay for themselves with your data or with degraded quality. We'd rather charge honestly and keep the product sharp, and if it stops earning its keep, you can cancel and take everything with you.
Unchecked, sometimes. That is exactly why the fact-checking engine exists: kept facts are cross-referenced with cited sources, wrong values are amended before you memorize them, and genuinely contested claims are labeled disputed rather than presented as settled.
You come back to the same few-minute hand you'd get on any other day. There's no backlog waiting for you. The schedule quietly adapts underneath: mature knowledge decays slowest, and a lapsed card picks up near where it left off instead of starting over. You'll even find a rabbit hole waiting, written about whatever slipped, to pull you back in.
Yes, always: one click exports everything as structured JSON or human-readable Markdown. You keep everything you learned, even after you cancel.