Mate in 2, white to play

Don't mention it. More useful because the "could analysis" requires you to fork out.

incredible that stockfish doesn't find the mate in 2 moves

Chess engines do not evaluate moves that does not seem to improve the position. It seems that the Stockfish configuration that runs in the browser does this more aggressively when it has a limited depth compared to unlimited depth. The engine does not consider Qa8 to be a viable move "at first glance" and ignores it.

Even with a limited depth this behavior most likely depends on the configuration on the engine and an engine running in the browser may behave differently compared to an engine running on desktop.

thank you very much for this explanation, much appreciated. When they asked Magnus to solve this puzzle he responded almost immediately (within 30 seconds) Qa8 . . . (youtube link is on page 1) there I got the puzzle from.

@randomchessguy52 I don't know if the name of the lady with the purple shirt is Tania, maybe another puzzle to solve who she is.

Usain Bolt couldn't run 100m in an hour if you kept him on a leash. That's what you did by restricting the calculation time on SF. Also note that chess.com's SF serves thousands of users simultaneously by making calculations for all of them. Don't think you have one SF all for yourself, more like 1/10000 of a SF!

alright this works as well. 

Is this puzzle even suitable for solving (e.g. in survival mode in puzzle rush)? We now know there are different solutions and Arisktotle and ch_dossier explained that we cannot or shouldn't even expect a chess engine to solve it within a few seconds. 

My question is: in case there are multiple choices for solving puzzles, imho it is wrong for the engine to "say", wrong try again, it could give some points or no points if an alternative solution is made.

Stockfish runs on your computer in the browser and not on Chess.com servers. It has all the computing power of your PC for itself

This is an implementation of Stockfish for browsers - https://github.com/nmrugg/stockfish.js/

You can see why Chess.com does not update the engine to v15 which can run only in newer browsers - they are still using v11 which can run in older browsers.

From the website:

This is a multi-threaded engine, and will only run in newer browsers and node.js versions. For an older JS and WASM version, see the Stockfish.js 11 branch.

How can White play Rc4? Don't you mean Black plays Rc3?

Oh I see, very interesting.... thank you alot for your comment  

Yes I guess meant black plays Rc4, Rc3 just prolonges the forced checkmate for 1 move. 

If it's White to play and mate in 2, that's good enough.

1. Qa8 Rc4 2. Nd6# , this is M2. Every move which is not Qa8 doesn't lead to M2. It leads to M3. 

What I was trying to point out is that a mate in 2 puzzle is "suitable for solving" as you put it in #29  if there is a unique move that forces mate in 2 (and there is no forced mate mate in 1 or 0). The puzzle is therefore OK.

(Btw 1.Qd1 among others doesn't lead to mate in 3.)

That is interesting, didn't know that. Does chess.com explain this anywhere? Chess.com gave us SF15 NNUE for a while and then it suddenly disappeared. I thought that was due to overload handling but now I don't know any more.

You can easily see that the engine is running in the browser just be observing the higher CPU usage during analysis in Task Manager on Windows or just by hearing the fans of your computer ramping up (depends on your computer).

You can also see that the engine is loaded in the browser using Developer tools in Chrome.

@ch_dossier thanks alot for your additional information, much appreciated.

Thx! I am insufficiently familiar with the architectural tools. For instance I always thought SF used my memory to stash away intermediate results and tables but not to run the algorithms. My computer is kind of old now and I leave it as is to prevent crashes or overloads. I'll be a bit more adventurous with the next one!

Considering the performance of contemporary chess engines and CPUs any computer (including mobile phones) are more than sufficient to run a chess engine. There is no real reason why this should be done on a server apart from competition between chess engines or really deep analysis. For deep analysis you an also run the desktop version of the engine that can take advantage of the full power of your computer. Stockfish does not use graphics cards but some engines do - https://www.chessprogramming.org/Category:GPU

A typical contemporary CPU is more powerful in raw performance compared to the famous Deep Blue 

Deep Blue - 11.38 GFLOPS - https://en.wikipedia.org/wiki/Deep_Blue_(chess_computer)
Contemporary CPU - https://setiathome.berkeley.edu/cpu_list.php

This does not take into an account the graphics card (GPU) since Stockfish does not use it.

If you factor the advancement in chess engines - any computer or phone is more than sufficient.

Also - keep in mind that using GFLOPS (Giga Floating-point Operations Per Second) to measure performance is misleading. A chess engine most likely do not use floating-point operations but checks and branching which have been extremely optimized in contemporary CPUs. Not to mention memory access performance. Therefore, any contemporary computer most likely far outperforms Deep Blue.

Whatever your computer is - you can be sure it will crush Kasparov (or Magnus)