About Flow Puzzle Solver
Who makes the site, where the solver came from, how the puzzles and lessons are checked, and how the site is paid for.
Flow Puzzle Solver is a site for people who play Flow-style puzzles, also known as Numberlink. It has original puzzles with hints and step-by-step walkthroughs, lessons on solving techniques, help pages, and a solver that reads a screenshot of a board and finds the answer on your own device. The site is created by Kevin Savill.
The site is independent. It is not affiliated with, endorsed by or connected to Big Duck Games, the maker of Flow Free, or any other puzzle publisher. Every board on the site is original.
Where the solver came from
The project began as an open-source Python toolkit for solving Flow-style puzzles on arbitrary graphs. Besides ordinary square and rectangular grids, it handles holes, walls, bridges, hexagonal grids, circular boards and warps that join one edge of the board to another, and it can import puzzles from screenshots. The source is on GitHub at ksavill/universal-flow-game-solver.
The browser edition at /solve/ is a narrower version built to run entirely on your device. Image reading, board editing and solving all happen in your browser, with the Z3 solver compiled to WebAssembly. No server ever receives your images or boards. It reads square and rectangular boards from 2 × 2 to 20 × 20 with holes, but not yet bridges, warps or hexagonal boards. How the solver works explains each step.
How the content is made
Each puzzle starts with a generator that draws a random arrangement of paths covering the whole board. The exact solver then proves the board has exactly one solution. A second solver, limited to the techniques a person would use, has to finish it without guessing. Boards that fail either test are thrown away. The second solver's moves become the walkthrough. Its rough notes are then rewritten in plain language with AI assistance, checked against the board position at every step, along with the puzzle's name, introduction and hints. A separate check re-proves every published puzzle and replays its walkthrough to confirm the steps still reach that one solution.
The lessons are drafted with AI assistance and checked against the same exact solver. Any diagram that claims something about solutions, such as "this board has exactly one answer" or "these dots can't all be connected", is verified automatically by the solver before the page is published, and a diagram that fails the check is fixed first. Diagrams that show a partial position or a wrong move are checked by eye.
If you spot a mistake anyway, the contact page explains how to report it.
How the site is funded
The site is free to use and needs no account. It may carry optional advertising on lesson, help and about articles and on puzzle pages. There is never any advertising in the solver, and you never need to view or click an ad to see a hint, a walkthrough or a solution. The home page and section index pages carry no ads either. Privacy and advertising describes exactly when Google's advertising code loads and what choices you have.