Gatesmith: the daily logic-gate puzzle
Gatesmith hands you a truth table and a box of logic gates, and asks you to wire a circuit that reproduces every row. That is the whole game. The depth comes from the scoring: fewest gates wins, and the server has already found the smallest circuit it could, so you always know what you are aiming at. A new puzzle arrives at midnight UTC, the same one for everyone, and there is a leaderboard for the day.
A round, step by step
- Read the story and the table. The story is flavour. The table is the contract: for every combination of inputs on the left, your circuit must produce the outputs on the right. Two inputs make four rows, three make eight, four make sixteen.
- Check which gates are allowed. Easy days allow NOT, AND and OR. Harder days restrict you, often to NAND alone, which is where the universality of NAND stops being trivia and starts being the puzzle.
- Drag gates onto the board and wire them. Inputs are on the left, outputs on the right. Click an input to flip it and watch the live truth table on the side fill in; rows you already match are highlighted.
- Press Check circuit. If any row mismatches, the game lists which ones. If every row matches, you can post a nickname to the leaderboard and copy a spoiler-free result to share.
- Try fewer gates. Beating the "best known" count is rare but possible on days marked as not proved minimal. Your lowest count for the day is what the board keeps.
What counts as a gate
Only gates that feed an output are counted. A stray AND left on the board costs nothing. NOT counts as one gate, like any other, which is why NAND-only puzzles are interesting: an inverter is NAND(A, A), and knowing when to spend one is the skill. Inputs and outputs are free. Wires are free. Reusing a signal is free, and is the single biggest trick in the game: compute A XOR B once and feed it to two places rather than building it twice.
Par: how "best known" is computed
Before a puzzle is published, the server runs an exhaustive search over small circuits built from the allowed gates, looking for the fewest that reproduce the table. The search is bounded, so on some days it proves the minimum and on others it only finds the best within its budget. The game tells you which: "optimal" means proved, "best known" means a smaller circuit might exist. The archive marks unproved days with an asterisk. If you beat an unproved par, the leaderboard records your count and the archive page for that day shows it.
Hints and the forge
The Hint button asks our own AI, running on our own hardware, for one sentence. It sees the puzzle, your current circuit and the rows that are still wrong, so the hint is about your attempt, not a canned tip. Hints are limited per day so the service stays responsive for everyone, and the first press is always gentle. Under "More puzzles" you can also forge a new puzzle on demand at a chosen difficulty. Forged puzzles go through the same validation as the daily: parsed, evaluated, rejected if trivial, and searched for a par.
Practice puzzles
Fourteen hand-made puzzles cover the standard circuits in rough order of difficulty: AND from NAND, XOR from NAND, a half adder, majority, a multiplexer, a full adder, parity and so on. They never change, there is no leaderboard, and each Learn guide points at the ones it teaches. If today's daily feels out of reach, do the two practice puzzles its gate set resembles and come back.
Strategy
- Count the ones. An output that is 1 in exactly one row is an AND of literals. One that is 0 in exactly one row is an OR of literals. One that is 1 in half the rows is often XOR-shaped or a copy of a single input.
- Look for inputs that do not matter. If flipping an input never changes an output, that input must not be wired to anything on that output's path. The archive's walkthrough does this check for every past puzzle so you can see the pattern.
- Write the formula first. Gatesmith shows the Boolean formula of your circuit live. Decide the formula on paper, then build it. Rebuilding by trial and error is slow and rarely minimal.
- De Morgan is your friend.
NOT (A AND B)isNOT A OR NOT B. Switching between the two forms is how you move inverters around until some of them cancel. - Two outputs share. Two-output puzzles almost always have a signal both outputs want. Find it first; it is usually where the par is hiding.
How puzzles are made and checked
Each night the designer writes a story, names the inputs, and gives one Boolean rule per output. The server does not trust the designer. It parses each rule, evaluates it into a truth table, and rejects the puzzle if any output is constant, equal to a single input, or a repeat of a recent day's function. Then the search for the smallest circuit runs. Only a puzzle that survives all of that is stored for the day. If the designer is unreachable at midnight, one of the practice puzzles is used instead, so there is always a daily. The archive shows every finished day with its truth table, the reference circuit written out as a netlist, and a walkthrough computed from the data.
The simulator
The same editor that powers the puzzle is available as a free logic gate simulator with no puzzle attached: all seven gate types, D and JK flip-flops, modules you can save and reuse, a clock pulse button, and a live truth table for anything combinational. The Learn guides open their examples there.
Questions people ask
Why did my correct circuit not count?
Open inputs read as 0, so an unwired gate pin is a silent zero. And a feedback loop that never settles shows a yellow X and fails the table. Check both before assuming the checker is wrong.
Can I replay an old daily?
Yes, from its archive page. Late solves are not added to that day's leaderboard.
Is there a time limit?
No. The day ends at midnight UTC; until then you can post, improve and repost as often as you like.