Free chess engine online: Stockfish in your browser, no account

Stockfish, the strongest chess engine, is free and open source, and it runs inside a web page. You can analyse a position on a phone or a laptop without installing anything. The free analysis board runs Stockfish on your device, needs no account and has no daily limit.

Is there a free chess engine you can use online?

Yes. Stockfish has been free from the start, and it has won most of the big computer chess events for years. What differs from site to site is how you get to it: some boards cap free analysis, some want you to sign up first, and some send your moves to a server.

The analysis board on Chesslord loads Stockfish into your browser. It downloads once, about 2 MB, and after that everything runs on your device, so nothing you play is sent anywhere.

How do you analyse a position with Stockfish?

Open the board

Go to the analysis board. It starts from the initial position, and Stockfish starts thinking straight away.

Load your position or your game

Paste a FEN to load a single position, or a PGN to load a whole game. Ctrl+V (Cmd+V on a Mac) anywhere outside a text field does the same.

Read the arrow and the number

The arrow is Stockfish’s best move. The number is the evaluation from White’s side: +1.20 means White is better by a bit more than a pawn, and M3 means mate in three.

Try your own move

Play the move you were thinking of. Stockfish answers from the new position, and Back to the game puts the original moves back.

What is the difference between FEN and PGN?

FEN describes one position in a single line of text: where the pieces are, who is to move, and whether castling is still allowed. PGN records a whole game, move by move, with the players and the result. Most chess sites let you copy both.

If you only care about one moment, paste the FEN. If you want to step through the game and find where it turned, paste the PGN.

Where do you get the FEN or the PGN of your game?

On chess.com and Lichess, open the finished game and look for the share or export option. Both give you the PGN of the game and the FEN of the position on screen. Copy it, open the analysis board and paste.

If all you have is a screenshot or a diagram in a book, there is no FEN to copy. Image to board reads the picture and sets the position up on a board. It needs a free account.

How deep does the engine look?

The depth is how many moves ahead Stockfish has searched. It keeps climbing while you watch, faster on a new laptop than on an old phone, because the engine runs on your device.

Most positions don’t need a big depth. A few seconds is enough to catch a hanging piece or a missed tactic. Sharp positions need longer, and the settings let you choose how long it thinks, from 5 to 60 seconds, and how many lines it shows, from one to three.

Is a browser engine as strong as the downloaded one?

It is the same engine. The browser version runs a little slower than a program installed on a fast computer, so it takes longer to reach the same depth. For checking your own games that hardly matters: it is still far stronger than any human player.

What won’t a free chess engine do for you?

• Explain in words why a move is good. You get a move and a number, and working out the reason is up to you
• Label every move of a game as good, inaccurate or a blunder
• Help you during a game. Engine help in a game you are playing breaks the rules on chess.com and Lichess, and over the board too

Labels on every move are what a game review gives you.

How do you get the most out of an engine?

Decide what you would play, and why, before you turn Stockfish on. Then compare. Spend your time on the positions where you and the engine disagree.

Look at the second and third lines too. If the best move is far ahead of the others, the position had one answer and you needed to find it. If the three lines are close, several moves were fine and you can move on.