What people ask first.

Yes. No ads, no account of its own, no paid tier. It's built on the open source chess world (Lichess's board, rules library, puzzles and opening explorer, Stockfish, and FSRS), and its own code is open under the GPL. If it helps your chess, you can chip in.

Not necessarily. For the parts that come from your games, connect Lichess (Lichess requires a login to download your games) or just add your Chess.com username (Chess.com games are public). Your puzzle history needs Lichess. Checkmate patterns, tactic sets, traps, studies and the fundamentals work with neither.

Yes. Add your Chess.com username on the Your plan page or under Add cards, My games. Chess.com games come without computer analysis, so Stockfish analyses them on your device: the first scan takes a little longer.

You approve read-only access on Lichess's own page; the app never sees your password and can't play, post or change anything. The access key stays in your browser. To sync, the server keeps only a one-way fingerprint of it, to recognise you.

Yes, on iPhone and Android alike. Open the app in your phone's browser and add it to your Home Screen. On iPhone: Share, then Add to Home Screen. On Android, in Chrome: the menu (three dots), then Install app (or Add to Home screen). It then opens like an app, works offline, and the browser keeps its data safe.

Fewer than you think. Six a day is a good start. Every new card comes back several times over the next weeks, so reviews build up later. Raise it once your daily reviews feel easy: Study load shows what the next month will ask of you before you change anything.

Just study what's due; the most overdue come first. If it's a lot, open Study load and cut new cards for a while (or limit reviews for a busy week) until you've caught up.

If you play regularly, corrective: your own repeat errors give the most for the least time. If you're new to chess, start proactive with the foundations: board safety, checkmate patterns, traps. Your plan decides this for you if you let it.

Outside opening lines, any move Stockfish rates about as good as the card's counts. Opening and study cards drill one line on purpose; when you play another move from the same study, the app says so instead of marking it wrong.

Some errors are slips: a piece or a mate given away with almost no time or almost no thought, or anything played with the clock nearly gone. You usually see those a second later, so drilling the position teaches little. They still count in Insights. Fast errors that aren't obvious do become cards: retraining those reflexes is exactly what drilling is for.

Two ways. After every scan, the app checks whether positions you've drilled came up in your games and whether you played the trained move; Insights shows the tally, and a card you got right in a real game counts as a successful review. And scanning again after a month shows what changed: your error rate, the positions you used to repeat, the tactics you missed.

It measures your thinking time on each move, against your own past times on that card. It never stops you. An optional speed goal (Bullet, Blitz, Rapid) only decides whether a card can count as Easy.

Puzzles and Lichess's review show you a position once. Here every position comes back on a schedule until you see it instantly, you play whole lines, your errors are ranked by what they cost, and the app finds the ones you repeat.

Rebuilding never resets a card you've already started. To start completely fresh, archive your decks first: nothing is deleted, and you can bring them back.

I do: Samuel Wexler, a musician and polyglot who wanted the way I study languages to work for chess. The story is on the home page. It's an early version that I use myself and refine as I go.