Frequently asked questions

Last updated 23 July 2026

What is OpenBook?

OpenBook is a free chess opening trainer — a repertoire builder and practice tool in one. You build an opening repertoire using real game data from players at your level, then drill it with spaced repetition until it sticks. Two modes, one job — opening prep. No courses, no videos, no puzzle sidebars.

Is it really free?

Yes — free with no ads, no paid tier, and no trial that expires. That includes saving up to 40,000 positions (20,000 for each color). It's cheap to run (the engine analysis happens in your own browser, and the opening data is aggressively cached), so it can stay free. If you want to support it, there's a donation link in the menu; nothing is behind it.

Do I need an account?

No. Guest mode gives you the full app — building, practice, engine analysis, imports — with your work stored in your browser. Signing in (free, via Lichess) keeps your repertoire on the server and synced across devices, and if you sign in after working as a guest, OpenBook offers to merge your guest work into the account.

I play on Chess.com, not Lichess. Is OpenBook still for me?

Yes. An opening repertoire isn't site-specific — the lines you drill in OpenBook are the lines you'll play anywhere. The move statistics come from the Lichess game database because it's open and free, but at any given level people play the same openings on both sites; just set your rating in the menu (Chess.com ratings tend to run a bit lower than Lichess ratings at the same strength, so it's fine to round up). And Review Games works with Chess.com directly — it can fetch your recent Chess.com games and show you where they left your prep. You can use guest mode with no account at all, or create a free Lichess account just for signing in — it takes a minute and you never have to play a game there.

Where do the move statistics come from?

From the Lichess opening database — billions of real games, released as public-domain data (CC0) — filtered to players around your rating, with a masters database overlay (★) showing what titled players prefer. Engine evaluations come from Stockfish running in your browser.

How does practice work?

Each line in your repertoire is a flashcard. OpenBook uses spaced repetition (an SM-2-style scheduler, the same family as Anki): lines you miss come back sooner, lines you know keep getting pushed further out. The Practice tab shows how many lines are due; a few minutes a day keeps a large repertoire sharp. You can also save any part of your repertoire as a named set and drill just that. Sets double as a pre-tournament review — a set drills every line it contains, not just the ones due, without inflating your review intervals. And when nothing is due, you can keep practicing anyway: a shuffled run through your lines that leaves the schedule untouched. The Map tab shows your whole repertoire's health at a glance — every line colored by how well you know it — so you can spot decay and drill the weak spots directly.

What counts as getting a line right?

A line is one flashcard, and it is graded all or nothing: a single wrong move anywhere fails the whole card for that review. Missing one move out of twenty counts the same as missing several. A miss is not a full reset, though — the line keeps 40% of its interval rather than dropping back to one day, so one fumble deep in a long line doesn't throw away months of spacing. A missed line then repeats right away, and keeps repeating until you play it clean, so you never leave a review having played a line wrong.

What is "ease", and what is it based on?

Ease is a measurement shown on each line in the Map, and it's what decides how fast that line's interval grows: the gap before the next review is multiplied by it each time you get the line right. Every line starts at 2.50. A correct review nudges its ease up by 0.05 (to a maximum of 3.00), and a miss drops it by 0.15 (to a floor of 1.30). It is based on nothing but your own history with that one line, so prep you keep missing keeps coming back more often than prep you always get right, without you having to flag it yourself.

How does OpenBook handle transpositions?

OpenBook stores your repertoire by position, not by move order. If two different move orders reach the same position, they share the same prep automatically — save a reply once and every route to that position knows it.

Can OpenBook check my actual games against my repertoire?

Yes — that's Review Games, in Build mode. It fetches your recent games from Lichess and/or Chess.com (no account linking — just a username) and replays each one against your prep. You see where you played the wrong move, which opponent replies you had no answer prepared for, and where your prep simply ran out. Repeat offenders across games group together and rise to the top, and clicking any finding jumps straight to the position so you can fix it. It runs entirely in your browser — your games and usernames are never sent to OpenBook's servers.

Can I import a repertoire I already have?

Yes — OpenBook imports standard PGN, so you can bring a repertoire from anywhere. Lichess studies are the easy case: browse your studies right in the app, pick the chapters you want, and import — each chapter comes in as its own line, variations included, filed under the right color. Course exports from other trainers work the same way. Annotations come along too: comments in the file become position notes, and if one differs from a note you already wrote, you review both and choose which to keep. Imports merge into your existing repertoire — nothing gets deleted, so re-importing an updated study is safe. There's room for 20,000 positions per color.

Can I get my data back out?

Anytime. Menu → Export gives you a standard PGN of your lines and position notes (usable in any chess app) or a complete JSON backup including practice progress. You can delete your account — and all your data with it — from the same menu. No lock-in is the point.

Is my repertoire safe?

Your repertoire lives in a managed Postgres database with point-in-time restore and daily off-site backups, and because export is one click, you can keep your own copy too — a PGN works in any chess app, and a JSON backup restores everything including practice progress.

What makes OpenBook different?

Most opening tools either sell you a repertoire someone else wrote, or give you somewhere to store lines with no trainer around them. OpenBook is the tool for building your own: every move you save is backed by real game data at your level, then drilled with spaced repetition, checked for coverage gaps, second-guessed by Stockfish, and finally compared against the games you actually play online — so you find out which prep holds up and which doesn't. Your own repertoire ends up smaller and better understood than a bought one — and this way is free.

Is my data private?

There are no ads, no advertising trackers, and no analytics identifying individual users. Guest repertoires never leave your browser. The full details are in the privacy policy, which is short on purpose.

Who makes OpenBook?

One independent developer, who built it for their own opening prep and still uses it daily. It's been steadily updated since it launched (see the changelog) and feedback goes straight to the developer's inbox.

Does it work on my phone?

Yes — OpenBook is built for mobile browsers as much as desktop. Add it to your home screen and it behaves like an app.