Terms of use

Who may use Blunderbase

You must be 13 or older to use Blunderbase. If the law where you live sets a higher minimum age for a service like this one, you must meet that age too.

If you are under 18, or under the age of majority where you live if that is older, a parent or legal guardian must read these terms and the privacy notice and agree to them for you before you use Blunderbase. By agreeing, they accept these terms on your behalf and are responsible for your use of Blunderbase.

Blunderbase is not for children under 13. If you believe a child under 13 has an account, write to hello@blunderbase.app and it will be deleted.

What Blunderbase does

You give Blunderbase a Chess.com username, a Lichess username, or both. Blunderbase reads that username’s completed Rapid and Blitz games from that site’s public archive, analyzes them with the Stockfish engine, and turns the mistakes it finds into review positions. It can explain a position in plain words, from what the engine already proved. On Pro, your new games are analyzed on Blunderbase’s server, so they are ready without the app open.

Both archives are public, and Blunderbase signs in to neither site, so it cannot check that a username is yours. Give it your own accounts. To study someone else’s games, Pro has Players: you may follow any player’s public games there, and they are kept apart from your own. Blunderbase follows one username per site: a username you enter later replaces the saved one for that site, and the games already imported stay in your history.

Blunderbase reads completed games only. It never reads, shows, or analyzes a game that is still being played, and it has no browser extension, overlay, or board integration of any kind.

Fair play

Do not use Blunderbase during a live game, anywhere. Everything here is about games that have already finished, and using an engine while you play breaks the rules of every chess site and teaches you nothing.

Blunderbase’s practice board plays against Stockfish locally and is never connected to a game on another site.

Your account and your data

Your games, analyses, reflections, practice history and the players you follow are private to your account. Nobody else using Blunderbase can read them.

You can delete your account at any time. Deleting it deletes your imported games and everything derived from them. See the privacy notice for what is stored and for how long.

Paying for Pro

Blunderbase is free to use, and everything you can do on the free plan stays free. Pro is optional. It costs $4.99 a month or $39 a year, and those prices include any tax you owe: the amount shown is the amount taken. Pro renews on its own at the end of each period until you cancel. If the price ever changes, the new price applies from your next renewal and you will be told before that renewal happens.

If you are under 18, a parent or guardian must make the purchase or give you permission to make it.

Every new account has Pro for its first seven days, at no charge and without a card. A coach’s invite link can make that period longer; the link says how long. When it ends the account moves to the free plan on its own: nothing is charged and nothing renews unless you choose Pro.

Payments run through Creem, which is the merchant of record for every Blunderbase subscription. Creem is the seller on the transaction, sends your receipt, and collects and remits the tax. Your card statement will therefore read Creem and not Blunderbase. Blunderbase never receives or stores your card details.

Canceling and refunds

You can cancel at any time, in either of two places: the orders page Creem links from the receipt it emailed you, or by writing to hello@blunderbase.app. Canceling stops the next payment. It does not cut short the period you already paid for — Pro keeps working until that period ends, and the account then returns to the free plan.

Returning to the free plan changes what Blunderbase will do next, not what it already did. Your games, analyses, reflections, and practice history stay exactly as they are.

If Blunderbase is not what you wanted, write to hello@blunderbase.app within 14 days of a payment and that payment is refunded in full. You do not have to give a reason and nothing is deducted. After 14 days a payment already taken is not normally refunded — but write anyway if something went wrong, because a refund is a better outcome than money taken for something you could not use.

Creem carries out refunds, returning the money to the card or account it came from. Ask us before you ask your bank: a refund we approve is settled in days, and a dispute raised with a bank takes weeks. If we have not answered you within seven days, Creem’s own support will take the matter up on your behalf.

What Blunderbase does not promise

Blunderbase is a beta. It may be unavailable, it may lose a session, and its coaching may be wrong. Chess evidence comes from Stockfish and move legality from a chess library; the written explanations are generated and may be unclear even when the underlying evidence is correct. Do not treat anything here as a guarantee of improvement.

Blunderbase is provided as is, without warranty. Blunderbase is not liable for any loss arising from its use, to the extent the law allows.

Not affiliated with Chess.com or Lichess

Blunderbase is an independent tool. It is not affiliated with, endorsed by, or sponsored by Chess.com or Lichess, and neither site is responsible for it. Your use of those sites remains governed by their own terms. Puzzle packs use the Lichess puzzle database, which Lichess publishes under CC0; using it does not mean Lichess endorses Blunderbase.

Ending your use

You may stop using Blunderbase and delete your account at any time. If you are on Pro, we cancel your subscription before deleting the account. A pending payment or unconfirmed cancellation keeps your account intact until it can be resolved. Cancellation does not itself request a refund; the refund policy above still applies.

Blunderbase may close an account that is used to assist play during live games, or that is used in a way that breaks these terms. If we close a paid account for a reason that is not your fault, the unused part of the period is refunded.

Changes

If these terms change in a way that matters, you will be asked to read and accept the new version before you continue. The version you accepted is recorded with the date.

Contact

Write to hello@blunderbase.app.