Lumesweep: the minesweeper that never deals you a 50/50

01  What it is

Lumesweep is minesweeper, played in a browser tab. The rules are the ones you already know: a grid of covered tiles hides a fixed number of mines; open a tile and it shows either a mine, or a number counting how many of the eight tiles around it are mined. Read the numbers, work out where the mines must be, and open every safe tile to clear the board.

The four sizes are the classic ones. Beginner is 9×9 with 10 mines, Intermediate 16×16 with 40, Expert is the wide 30×16 with 99, and Master is 30×20 with 125 — the largest board in the app, and a real step past Expert rather than a re-run of it. Each size keeps its own best time, so a slow Expert clear never sits next to a fast Beginner one.

It is free, it runs entirely in your browser, and there is no account, no install and no download. Pick a size and the board is waiting for your first tap.

02  Your first tap is always safe, and always opens something

In most minesweeper implementations the layout is decided before you touch it, so your opening click is a lottery ticket: on the unlucky boards it is a mine, and on merely average ones it opens a single tile that tells you almost nothing.

Lumesweep generates the board at the moment you tap. The generator places mines everywhere except the tile you tapped and its eight neighbours, so your first tap can never be a mine — and it always lands on an empty tile, which means it always opens the wide cascade around it. Every board therefore starts with a region of numbers to reason from instead of a guess.

The clock starts on that tap rather than when the page loads, so a slow connection never costs you a time — and the layout is fixed from that moment on.

03  What the no-guess badge on the results card actually means

Classic minesweeper has a known flaw. Sometimes you reach a position where two covered tiles are equally likely to be the mine and no amount of careful reading separates them. You guess, you win or you do not, and the outcome had nothing to do with how well you played — players call it the 50/50.

Lumesweep removes those positions from the boards it serves. When you make that first tap, the generator does not simply scatter mines and hand them over — it plays the board with a deductive solver allowed only the information a human has: the numbers revealed so far, plus the flags it has worked out for itself. It applies the same steps a strong player uses, cheapest first: counting one tile's remaining neighbours, the subset patterns that run along walls (the 1-2-1 shape and its relatives), and then a bounded search over the frontier when neither is enough. If that solver can open every safe tile using forced moves alone, the board is served and marked verified.

Verified boards carry a NO-GUESS ✓ badge on the win card, and the badge is deliberately narrow: it is drawn only on a board whose solvability was actually proved, never as a blanket claim. If the generator cannot produce a verified board inside its reshuffle budget it serves the best board it found and does not badge it — the worst case is an ordinary board, never a false promise. The app's tests re-check every badged board on every preset, including the 30×20 Master board, through the solver.

The guarantee is not an easier game. Nothing is highlighted and no move is made for you; you still have to find every deduction — there are simply none of the positions where no deduction exists. Being stuck on such a board always means you missed something, which beats being stuck because the board is unfair.

04  Reveal, flag, chord — and what it takes to play on a phone

There are three moves. Tap a covered tile to reveal it. Long-press it on a touchscreen, or right-click with a mouse, to plant a flag. Then tap a revealed number once the flags around it match that number and every remaining neighbour opens at once: that is chording, and it is where the speed in minesweeper actually lives — a single well-placed chord can open a dozen tiles.

Two details on the mine counter. It counts mines still un-flagged, not flags you have placed — and it will go negative if you over-flag, because the app would rather tell you the truth than clamp the number. You also never have to flag at all: a board is won by revealing every safe tile, so flags are a private note to yourself.

On a phone the board is sized to the screen, so there is nothing to pinch or scroll. Holding a tile flags it with a short haptic tap, and sliding your finger off cancels the press instead of firing it — the difference between a flag and a mis-tap on a train. Keyboard and screen-reader play are first-class too: arrow keys move a cursor, Space or Enter reveals, F flags, C chords, R restarts, and 1–4 switch difficulty, with every tile labelled for a screen reader ("3 mines nearby", "Flagged", "Empty") inside an ARIA grid.

Sound stays off until you first interact with the page and mutes with one tap in the toolbar, and the cascade animation follows your system's reduced-motion setting, with a manual toggle beside it.

05  The clock, the streak, 3BV, and the card at the end

The timer runs live in the toolbar and reads to a tenth of a second, the precision the minesweeper community actually compares times at, while the best time kept for each difficulty holds full millisecond precision underneath. A new best is starred on the results card.

Clear a board and every remaining mine is flagged for you, and the card appears: your time, your win streak, and a number labelled 3BV. 3BV — the Bechtel Board Benchmark Value — is the minimum number of clicks needed to clear that particular board with perfect play, chording and cascading optimally. It measures how much work the layout contains, which is why raw times alone compare badly: two Expert boards can differ by hundreds of clicks of work, so a fast time on a light board and a fast time on a heavy one stop being the same claim.

Lose and the app stays calm about it: the remaining mines are revealed, any flag you placed on a safe tile is marked as wrong, and the streak resets to zero. Your best streak and best times survive the loss, because they were never the same thing as the current run.

The share button exports the card as a PNG image and hands it to your phone's normal share sheet; on a desktop, where no share sheet exists, it copies a line with your result and the link. The link carries the board's seed number, so whoever opens it gets the identical layout — same mine positions, same opening — and can try to beat your time on it, which is a better argument than a screenshot. A separate control copies the board link on its own, without your time attached, if you would rather race fairly.

Everything the app remembers — best time per difficulty, current streak, best streak — is stored in your own browser, on your own device: no account holds it and no server can lose it, and clearing your browsing data clears it. Play itself makes no server calls, so a loaded page keeps playing if the connection drops.

06  Questions people ask

Is Lumesweep free, and do I need an account?

Free, and no account. There is nothing to install, nothing to sign up for, and no paywall on any board size. The app is ad-supported and runs in your browser.

Is every board really solvable without guessing?

Every board carrying the NO-GUESS ✓ badge is — it was proved solvable by a deductive solver before you were shown it, using only the information a player can see. Boards that fail that check are served without the badge rather than mislabelled, so the badge is a specific claim about that specific board, not a slogan.

What does 3BV mean on the results card?

It is the minimum number of clicks needed to clear that board with perfect play, counting cascades and chords optimally. It measures how much work the layout contains, so it lets you compare two clears fairly: a fast time on a low-3BV board and the same time on a high-3BV one are not the same achievement.

Does it work on a phone, and does it work offline?

Yes to both. The board is built for touch — tap to reveal, hold to flag — and fits the screen without zooming or scrolling. The game itself makes no server calls, so once the page has loaded it keeps playing if your connection drops, and your best times and streak live in the browser rather than on a server.

Can I send someone the exact board I just played?

Yes. Sharing a result includes a board link carrying the layout's seed number, so anyone opening it gets the identical board — and a separate "copy this board's link" button sends the board on its own, without your time attached, if you want a fair race.

Where are my best times and win streak stored?

In your own browser, on your own device. Nothing is uploaded and there is no account, which also means the records do not follow you to another browser or phone, and clearing your browsing data clears them.

07  More from the shelf

• Tilewright — Draw seven tiles. Outword the AI.
• Chess — Beat the engine. Post the win.
• Fiveaside — Score past the keeper. Post the scoreline.
• Tierforge — Drag anything into tiers. Post the card.

Browse every app in the catalogue →