Privacy

Games. The public games of the chess username Luftchess is set up with (today, one player’s), fetched from the public Lichess and Chess.com interfaces: the moves, both players’ usernames and ratings, the time control, the clock times, the date, the result and the game’s link, as those sites publish them. Only standard chess is kept.

What the engine found. The engine’s evaluation of each move and the moments it flagged.

Your practice. Which positions you have seen, how each try went, and when each one is due again.

Your sign-in. A random session code in a cookie on your device. Our server keeps only a one-way fingerprint (a SHA-256 hash) of it, with when it was made, last used and when it ends. A sign-in lasts 30 days, or until you sign out.

The invite list. The Lichess usernames that are invited. When you sign in, Luftchess reads your username from Lichess, checks it against this list, and hands the Lichess access back at once. The access code is never stored.

Room counts. How many times each part of the app was opened on each day, with nothing about who opened it.

Preparing for an opponent. When you prepare for an opponent, Luftchess reads that player’s public games from Lichess or Chess.com (or the games you paste), keeps them at most 30 days (or until the day after your event) in a file left out of backups, and shows them to nobody else.

cc_auth: keeps you signed in. It is set only when you sign in, lasts 30 days, and scripts cannot read it.

cc_oauth: holds the sign-in with Lichess together for up to 10 minutes, then it is deleted.

Inside the app, your browser also keeps a few display choices (such as board and filter settings) and an offline copy of the app’s files. They stay on your device. These public pages set no cookies at all.

Hetzner rents us the server. Your data is stored there. The owner also keeps copies of the server’s recent backups offline, on the owner’s own computer, so that losing the server loses nothing (see 6.3).

Cloudflare carries the traffic between you and the server and protects it from abuse. It sees the requests pass, as any network provider does; its own logs expire on their own.

Lichess is asked for your public games and for your username at sign-in, and, when you prepare for an opponent there, for that player’s public games (see 2.7). For endings with seven pieces or fewer, the position alone (no names) is sent to the Lichess tablebase for its exact result. On the Analyse board, your browser asks Lichess’s cloud evaluation for engine lines of the position shown; only the position is sent, with no names, and Lichess sees your network address, as any website does.

Chess.com is asked for public games, by username, when a Chess.com username is set up, and for an opponent’s public games when you prepare for them there (see 2.7).

Inside the app, a few open-source libraries (listed on the licences page) load from public code networks: code.jquery.com, unpkg.com, cdnjs.cloudflare.com and cdn.jsdelivr.net. They see that request, as any website would. These public pages load nothing from anyone else.

Nobody else. No part of the app sends your games to a language model today. If that ever changes, this page will say so first.

Your games, analysis and practice are kept while you use Luftchess. Ask us and we delete them.

Sign-ins end after 30 days, or when you sign out.

The server keeps daily backups, and the oldest is replaced after 14 days. Deleted data leaves the server’s backups within that time. The owner keeps up to 14 offline copies (5.1): each time Luftchess is updated, the server’s newest backup is copied and the oldest copy is removed. Updates do not follow a calendar, so an offline copy can keep deleted data for longer than 14 days.

Server logs record sign-in events without usernames. To slow down repeated failed sign-ins, the network address of a failed attempt is held in memory for up to 15 minutes and never written to disk.