Sudoku-Land turns 20: from Flash to today

The domain name sudoku-land.com was registered on 28 September 2005 — right in the middle of sudoku's worldwide popularity wave, which had just exploded across Europe and the United States after its success in Japan. The .fr was taken at the same time, as a precaution, to keep control of the name.

The game itself was built in Flash (Macromedia at the time, before the Adobe acquisition). The site around it ran on PHP, but almost exclusively for includes — a simple way to factor out the header, the footer and the navigation across pages, without duplicating code everywhere.

Here is a video made at the time with Blender, as a 3D animation, introducing the rules of sudoku along with techniques and tips for beginners:

Adobe ended support for Flash Player on 31 December 2020, and started blocking Flash content from running outright on 12 January 2021. The major browsers (Chrome, Firefox, Edge, Safari) removed the plugin at roughly the same time.

The result: Sudoku-Land stayed online throughout all those years — the domain name was never dropped — but the game itself became unplayable, overnight, in any up-to-date browser. The site existed, it just no longer worked.

The complete rewrite of the site began in April 2026: not a single line of Flash left, everything in native HTML, CSS and JavaScript, with no dependency on a plugin that can vanish overnight. The 9×9 grids, the Kids/Junior/Junior+ variants, the teaching solver, the animated help, printing, dark mode — everything Sudoku-Land offers today dates from that rewrite.

A full rewrite is a chance to throw everything out. Exactly one thing was carried over as it was: the ring selector, visible in the screenshot above — the digits laid out in a circle around the selected cell, instead of a number pad sitting beside the grid.

Back in 2005 it was mostly an aesthetic choice: with a mouse, a ring and a row of buttons come to much the same thing. Twenty years later, the same component turned out to be the site's strongest argument on mobile — your thumb never leaves the grid, whereas a number pad at the bottom of the screen forces a round trip between the cell and the buttons for every single digit.

The number pad is still there, and the layout can be switched mid-game: some players prefer it, particularly on the smaller grids. A feature designed for a desktop screen in 2005 simply turned out to work better on a device that did not yet exist.

The 2026 version is written in plain HTML, CSS and JavaScript. No React, no Vue, no build step, no dependency to install: the files uploaded to the server are exactly the files that run in the browser.

That choice comes straight out of the story above. Sudoku-Land has already lost its game once, because it rested on third-party technology that went away — taking everything built on top of it along. A JavaScript framework is not a proprietary plugin, but the reasoning carries over: ecosystems move fast, a major version breaks the code of the last one, and a project left untouched for five years becomes very hard to pick up again.

A page written in plain HTML, CSS and JavaScript will still open in twenty years. For a site maintained by one person in their spare time, that is the only serious guarantee. The price is real — you write yourself what a library would hand you for free — but it is a known cost, paid once, and never one more dependency.

There is a concrete side benefit: pages load fast, and work on an old phone.

The rewrite did not just swap out the technology — it added everything the original game could never offer:

• Playing on a phone at all: Flash never ran on the iPhone, so from 2010 onwards the original site was simply unavailable to half its potential visitors.
• Playing offline: the site installs like an app and keeps its puzzles available, on a train or on a plane.
• A game picked up exactly where it was left, even after closing the tab — grid, clock and remaining help uses are saved continuously.
• A dark mode, a notion that did not exist on the web of 2005.
• Four grid sizes (4×4, 6×6, 8×8, 9×9) instead of one, and five difficulty levels.
• A step-by-step solver that explains the reasoning rather than giving the answer, plus animated help on the children's grids.
• A fully bilingual site, English and French, running one game engine with the text kept separate from the code.
• Printing, for playing on paper.

None of this was impossible in Flash in principle. The web simply changed shape in the meantime: in 2005 you visited a site on a desktop screen, once, online. Everything else follows from that.

In fairness, the comparison does not run one way only. Flash had two qualities the rewrite gave up.

Animation was free. A timeline, two keyframes, and the movement existed — without a line of code. In JavaScript and CSS, every animation on the site is written by hand: the animated help on the children's grids, the ring moving into place, the dark mode transitions. The result is better, lighter and more accessible, but it cost time on a completely different scale.

Rendering was identical everywhere. A Flash file looked exactly the same in every browser, because the plugin did the drawing. Today the same page has to be checked in Chrome, Firefox and Safari, in light and dark mode, from 320 pixels wide up to a desktop display. That is the trade-off for an open web, and it remains a far better deal.

Twenty years after the domain name was registered, Sudoku-Land never really disappeared — it just went through a long stretch where it existed without being playable. It works again, and better than before.