Copy the Rule 16 board into the solver
Rule 16 asks for the best move in algebraic chess notation for the board it shows you.game The board is picked at random from a fixed list, so your answer will differ from a friend's. Copying it takes about a minute.
Check which way up it is
If the game shows Black's pieces at the bottom, press Flip board so the solver matches it. Flipping only changes the view; the answer stays the same.
Place the pieces rank by rank
Go one row at a time, starting with the row nearest you. Pick a piece, tap its square, and repeat. Tap a square again with the same piece to remove it.
Set who moves
The game says under its board whether it is White or Black to move. In the puzzle list we tested, it is White in 150 puzzles and Black in 43.
Press Find best move
The solver checks the position first (one king each, no pawns on the back rows) and then calculates. Most Rule 16 boards take under a second.
Count before you solve. Every Rule 16 puzzle in our test is a mate in 2 for the side to move. If the solver finds no mate in 2, a piece is almost certainly on the wrong square, or the wrong side is set to move, and it will tell you so.
Read the answer: algebraic notation in one minute
Algebraic notation writes a move as the piece letter followed by the square it lands on. The solver writes this for you, but you need to read it to type it correctly. The full system is in our chess notation guide; this is the part Rule 16 uses.
Q R B N KQueen, rook, bishop, knight, king. Always a capital letter.h5+Pawn moves have no letter, just the square.xA capture, as in Rxh6+: the rook takes on h6.+The move gives check. It is part of the answer.#Checkmate. No Rule 16 answer in our test uses it.Rad8An extra file or rank shows which of two pieces moves.Here is what the 193 answers look like. Queen and rook moves are the large majority, and about a third are captures:
- Give check
- 184of 193 answers end in +
- Queen moves
- 75then rook 64, knight 28, bishop 20
- Captures
- 68contain an x
- Length
- 3–5characters; 111 answers are 4 long
Only 5 answers are pawn moves and 1 is a king move. The 9 answers without a + are quiet moves that set up a mate on the next move that the opponent can't stop.
Rule 16 traps: check symbols, captures and element letters
1. Leaving off the +
The game checks your password for one stored answer per puzzle.list If that answer is Rf7+, then Rf7 is a different string. Type the move exactly as shown, including the capital piece letter, the lowercase file and any x.
2. A different good move
Some positions have more than one winning move. The game accepts only the one it stored. In our test, every stored answer was a mate in 2 and the engine's first choice, so trust the solver's move over one you found yourself. That's also why the solver looks for a mate in 2 first.
3. Element symbols hiding in the move
Rule 18 later asks that the atomic numbers of every element symbol in your password add up to 200. Piece letters can form symbols with the file letter after them: Rf is rutherfordium, Ne is neon. In 80 of the 193 answers, the move contains a symbol. The solver shows any it finds.
| Letters in the move | Element | Atomic number | Answers |
|---|---|---|---|
Nh | Nihonium | 113 | 2 |
Rg | Roentgenium | 111 | 9 |
Bh | Bohrium | 107 | 3 |
Rf | Rutherfordium | 104 | 6 |
Ra | Radium | 88 | 1 |
Re | Rhenium | 75 | 7 |
Nd | Neodymium | 60 | 3 |
Rh | Rhodium | 45 | 8 |
Nb | Niobium | 41 | 1 |
K | Potassium | 19 | 1 |
Ne | Neon | 10 | 7 |
N (any other knight move) | Nitrogen | 7 | 15 |
B (any other bishop move) | Boron | 5 | 14 |
Be | Beryllium | 4 | 3 |
Counted the way element symbols are read: a capital letter, joined with the next lowercase letter when the two form a symbol. Q and R on their own are not elements, so moves like Qxh7+ or Rd8+ add nothing.
The four highlighted rows are the expensive ones: one symbol uses more than half of the 200. Those 20 answers still work. You just have less room for the other elements Rule 18 forces into your password, such as the V in a Roman numeral.
Which parts of the move matter for later rules
Once Rule 16 is satisfied, leave the move in place: it has to stay correct until the end. These later rules interact with it.rules The solver's result panel checks Rules 5, 18, 19 and 25 for your exact move.
| Rule | What it asks | What your move does |
|---|---|---|
| 5 | The digits must add up to 25 | Adds its rank number, 1 to 8. Most answers add 6, 7 or 8, so leave space in your other digits. |
| 9 | Roman numerals must multiply to 35 | No effect. K, Q, R, B and N are not Roman numerals, and the capture x is lowercase. |
| 18 | Atomic numbers must add up to 200 | Counts any element symbol in the move (see the table above). |
| 19 | Every vowel must be bold | Moves on the a- or e-file contain a vowel. 29 of the 193 answers do; bold that letter. |
| 25 | Give up two letters for good | Don't pick any letter in your move: the piece letter, the file letter or x. |
| 30 | Each digit's font size must be its square | Resize the rank digit: a 7 needs size 49, an 8 needs 64. |
| 31 | Repeated letters need different font sizes | Check the move's letters against the same letters elsewhere in the password. |
| 32–33 | Include the length, and make it a prime number | Adds 3 to 5 characters to the total. |
Rule 5 is where most players have to go back and change things. Fix the digit sum using the digits you control, never by editing the chess move.
If the game won't accept the move
- The wrong side is set to move. Look under the game's board again and switch White or Black.
- A piece is one square off. Count each row from the side, especially pawns and pieces near the edges. Use Flip board if the game's board is the other way up.
- The + is missing, or the letters are in the wrong case.
- You reloaded the page. The game then picks a new puzzle, so the old answer no longer applies.
- Something else in the password broke. Earlier rules can fail again as you edit. Scroll up and check which rule is red.
The solver flags the first two. If it says it found no mate in 2, or that the move doesn't give check, compare the board again before typing anything.
Method
We tested the solver on every Rule 16 puzzle
The game keeps its puzzles and their answers in its own code. We used a copy of that list that players extracted and published on GitHub, which has 193 positions.list A separate count by another player also found 193, with 184 ending in check.stats
- All 193 stored answers are legal moves, and each is written in standard notation exactly as a rules library writes it.
- Stockfish 16 (1 second per position, top 3 lines) chose the stored answer as its best move in 193 of 193 positions. Every one is a mate in 2.
- The engine this page runs in your browser (Stockfish 17.1, the same build as our analysis board) also matched 193 of 193 when we ran every position through this solver.
- In no position did the engine find a second move that mates just as fast, so there is one clear answer each time.
Tested November 14, 2026. If the game changes its puzzle list, we will re-run the test and update this page.
A note on fair play: using an engine for a single-player puzzle like this one is normal. Using one during a rated game against another person is cheating on every major chess site. Read more in is using a chess engine cheating?
Password Game chess FAQ
What is the best chess move for Rule 16?
There is no single answer: the game shows one of 193 puzzles at random. Copy your board into the solver above, set the side to move, and it gives you the move to type. In our test it matched the game's stored answer on all 193 puzzles.
Do I need to include the + sign?
Yes. Type the move exactly as the solver shows it. 184 of the 193 answers give check and end in +, and the + is part of the answer.
Why does the game reject my chess move?
Usually a piece is on the wrong square, the wrong side is set to move, or the + is missing. Each puzzle has one stored answer, so a different good move won't be accepted. See the checklist.
Is it White or Black to move?
The game tells you under the board. In the list we tested, White moves in 150 puzzles and Black in 43. If the game's board has White at the top, press Flip board so the solver looks the same.
Does the chess move affect later rules?
Yes. Its rank digit counts toward the digit sum in Rule 5, its letters can form element symbols for Rule 18, and later rules ask you to bold vowels, give up letters and resize digits. The solver lists each effect for your move.
Can a chess move contain a Roman numeral?
No. Moves use the capital letters K, Q, R, B and N, and none of them are Roman numerals. The x for a capture is lowercase, so it isn't read as 10.
What if my move contains Rf, Rg, Bh or Nh?
Those pairs are element symbols with atomic numbers from 104 to 113, which is more than half of the 200 Rule 18 needs. The move is still correct; just leave room in your other elements.
Can I use the main move finder instead?
Yes, the chess move finder uses the same kind of engine. This page adds the Rule 16 checks: the side-to-move warning, the forced-mate check and the effects on later rules.
Is using a solver for The Password Game cheating?
It's a single-player puzzle, and the game's own hint links to an explanation of chess notation, so looking up the move is a normal way to play. Using an engine in a rated game against a person is different and breaks the fair-play rules of every major chess site.
Sources and method
- The Password Game by Neal Agarwal (neal.fun), Rule 16: “Your password must include the best move in algebraic chess notation.”
- pog5/nealpasswordgame (GitHub): a players' breakdown of the game with the puzzle positions and stored answers (chess.jsonc), and the rule list used above.
- Simplified rule list from the same project. The game can change; check the rule text on screen.
- The Password Game: strategy & statistics: an independent count of the chess answers and the element symbols in them.
- Stockfish, the open-source engine used for the solver and the test.
Every statistic on this page comes from our own run over the 193 positions, with legality checked by python-chess and moves calculated by Stockfish. The Password Game is made by Neal Agarwal; Chess Move Finder is not affiliated with it. Spot an error? Tell us. Related: how to find the best chess move and the board editor.