This isn't really static right? It's still dynamically rendered by the backend each time you request the page. There aren't 999999919291293923 pre-rendered pages living on a server somewhere.

Technically speaking, it would require ~ 4.8 * 10^44 pages to cover all legal chess positions [1]. But they're happy to serve utterly illegal positions like https://chess.maxmcd.com/rnbqkbnr/qqqqqqqq/8/8/8/8/QQQQQQQQ/... as well.

[1] https://github.com/tromp/ChessPositionRanking

The above illegal position example was a checkmate in one, this one is more fair: https://chess.maxmcd.com/rnbqkbnr/qqqqqqqq/qqqqqqqq/8/8/8/QQ... ;)

OK, this one is definitely more fair: https://chess.maxmcd.com/rnbqkbnr/qqqqqqqq/qqqqqqqq/qqqqqqqq...

Static as in no XmlHttpRequest.

I can start a game on Lichess, resign it right away, enter analysis mode, then disconnect from the internet and continue to use the board (in the same way that one can use the board on site we are discussing here), so Lichess's analysis board does not use XmlHttpRequest either.

You don't need to resign a game to enter analysis mode. It's available from the menu.

> There aren't 999999919291293923 pre-rendered pages living on a server somewhere

There are. They're just compressed with an application-specific compression approach.