Methodology

How PuzzleDaily generates, validates, and publishes each day's puzzles. We document this in detail because every published puzzle is meant to be reproducibly correct, fair to all players, and free of guess-and-check positions that turn a deduction game into a lottery.

Generation

Each game on PuzzleDaily — Crossword, FlipArt, Nonogram, SpellTower, and TypeShift — has its own generator program. Generators run automatically once per UTC day at 00:00 UTC. They are seeded deterministically from the date so that the same calendar day produces the same puzzle for every player. There is no per-region rotation, no A/B variation, and no human curator selecting puzzles from a backlog.

Source data is public-domain. Word games draw from the open-source Scrabble word list (TWL or SOWPODS depending on the game), filtered against a community-maintained block-list to exclude offensive terms. Number games draw from straightforward integer constraints (prime sequence, digit-position constraints, parity rules). Geography games (when applicable) draw country geometries and centroids from OpenStreetMap.

Validation

Every generated puzzle is solved by our in-house solver before publication. The solver does what a careful human solver does: applies logical deduction from the published clues without guessing. A puzzle that the solver cannot fully resolve gets rejected and regenerated. A puzzle that admits multiple valid solutions also gets rejected. The published puzzle is one we have proven solvable through deduction alone.

Word puzzles get an additional validation pass against the corpus we publish them against. If the generator accepts a word as valid but the corpus excludes it (or vice versa), the puzzle is rejected. This catches a class of subtle bugs where the generator and the published dictionary drift apart between releases.

Difficulty calibration

A small pilot-tester group solves each candidate puzzle before it goes live. We publish the puzzle only if its pilot solve metrics (median solve time, median number of guesses, solve-rate across pilot testers) fall inside the published difficulty band for the target day of the week. Mondays through Wednesdays are calibrated easier; Thursdays through Sundays harder.

The pilot pool is small (~20 testers per game) and biased toward regular puzzle players. That means an individual published puzzle can hit a corpus or pattern unfamiliar to a typical player and run harder than the calibration suggests. We treat persistent solve-rate drops below 50% on a single day as a calibration issue worth flagging in the next release; the published puzzle itself is not corrected after the fact because rolling back a published puzzle would be unfair to players who already solved.

Limits of what this process can and cannot guarantee

The validation pipeline catches three classes of problem: puzzles with no solvable path, puzzles with multiple valid solutions, and puzzles whose accepted vocabulary mismatches the published corpus. It does not catch every possible quality issue. Specifically:

• An esoteric valid word the generator accepts but most players have never seen. The puzzle is technically solvable; it just feels unfair.
• A clue pattern that is logically deducible but requires several minutes of dense reasoning. Solver agrees the puzzle is fair; humans may disagree.
• An aesthetically poor puzzle (boring repeated letters, all-vowel rows, etc.). The validator is correctness-focused, not aesthetics-focused.

When a player surfaces one of these issues, we update the generator constraints for future days rather than retroactively edit the published puzzle. The aim is consistency over perfection in any given day.

Data sources and licensing

The Scrabble word lists used by the word games are open-source — TWL (Tournament Word List) and SOWPODS are publicly available. We use them under the terms of their published distribution licenses. The OpenStreetMap data used by geography games is licensed under the Open Database License (ODbL); attribution is included in the page footer where OSM data appears.

Per-puzzle answer keys are not source data; they are computed by the generator from the source corpora. The generator code is open-source on github.com/timcadair so that any player can inspect the generation logic, audit the validator, or fork the project.

Frequently asked questions