Not a lichess tool but I have a simple idea to do this with a chess interface that supports any chess engine with a polyglot opening book.
Let us say you use xboard with stockfish and a polyglot opening book mybook.bin. Now you play against the engine. As long as you are making moves that are within mybook.bin, the engine responds from the book immediately, and when you make a move that is outside mybook.bin, the engine starts to take some time to respond. So you immediately know that you made a move outside the book. Now you can abort the game if you wish and study on your own if the move was bad or why it was bad or if you found a novelty. Or if you wish you can continue the game.
This setup does not depend on what engine you use. You can use any other engine with the same book, and it will make instant moves as long as you are within the book.
Now you can change the books. You can use a book with only variations played by top players or you can play with a book that is more varied, and possibly has variations that top players may consider not playable. A book such as varied.bin (I think comes with scid, but not sure) assigns equal probabilities for all moves in the book. You can also build your own opening book using a collection of games.
I think in scid vs pc if you play a game against an engine, it warns you when you leave the book, and asks you if you want to continue the move.
This is a simple setup anybody can use on their computer. In fact with this setup you can play dozens of games spending 3-4 minutes on each.
Not a lichess tool but I have a simple idea to do this with a chess interface that supports any chess engine with a polyglot opening book.
Let us say you use xboard with stockfish and a polyglot opening book mybook.bin. Now you play against the engine. As long as you are making moves that are within mybook.bin, the engine responds from the book immediately, and when you make a move that is outside mybook.bin, the engine starts to take some time to respond. So you immediately know that you made a move outside the book. Now you can abort the game if you wish and study on your own if the move was bad or why it was bad or if you found a novelty. Or if you wish you can continue the game.
This setup does not depend on what engine you use. You can use any other engine with the same book, and it will make instant moves as long as you are within the book.
Now you can change the books. You can use a book with only variations played by top players or you can play with a book that is more varied, and possibly has variations that top players may consider not playable. A book such as varied.bin (I think comes with scid, but not sure) assigns equal probabilities for all moves in the book. You can also build your own opening book using a collection of games.
I think in scid vs pc if you play a game against an engine, it warns you when you leave the book, and asks you if you want to continue the move.
This is a simple setup anybody can use on their computer. In fact with this setup you can play dozens of games spending 3-4 minutes on each.