Play a free Akari puzzle in your browser by loading a fixed 5 by 5 Light Up board, marking every white cell with a light or an X, and finishing on a deterministic 1,000-point score. Akari, also called Light Up, is a placement puzzle about coverage and restraint: you put a light on a white cell and that beam travels along the row and column until a black wall or the board edge stops it, illuminating every visible white cell along the way. The objective is to illuminate every one of the 20 white cells while ensuring that no two lights share an unobstructed row or column. Four of the black walls on the board carry a small number, and that number must equal the count of lights in its four orthogonal neighbors exactly. The published rule set is owned by Nikoli under the Akari name, while Simon Tatham's maintained Light Up documentation describes the same essential constraints, so the same logic carries across both titles. A free online version is offered as a browser-only fixture: no download, no account, no daily download, and no random board, so the same 5 by 5 puzzle is solved every run.
Light Up (Akari) Rules in Plain English
An Akari board is a square grid divided into two kinds of cells. Most cells are white and serve as both the corridors that lights must illuminate and the only legal homes for a light. The remaining cells are solid black walls. Some walls carry a small printed number from 0 to 4; the rest are unnumbered and only act as beam blockers. Once you place a light on a white cell, its beam travels in the four orthogonal directions, up, down, left, and right, and keeps going until it hits a black wall or the edge of the board. Every white cell the beam touches becomes illuminated, including the cell that holds the light itself. Two lights may not share an unobstructed row or column, which means their beams must be separated by at least one black wall or by the board edge. Finally, every numbered wall is checked against the four orthogonal cells around it, and the number is exactly the count of adjacent lights.
The result is a placement puzzle with two competing pressures. You want enough lights to cover every white cell, but you do not want so many that they conflict with one another or overflow any clue. A 5 by 5 board is small enough to hold in working memory but dense enough to demand real logical pruning. Most candidate placements can be ruled out before they are placed, which is why the genre is grouped with paper-and-pencil logic puzzles rather than arcade games. The free Akari browser fixture ships one such board, with 25 cells total: 20 white cells, four numbered walls, and one unnumbered wall, and its unique completed arrangement uses exactly five lights.
What marks mean on the board
White cells cycle through three states: clear, light, and X. The clear state is the default and means you have not yet decided. A light is a real placement that contributes its beam and its adjacency count to every numbered wall it touches. An X is a personal note that the cell should remain empty; it does not block a beam and it is invisible to the rule checker. Lit white cells get a distinct surface treatment so you can read the coverage map at a glance, and any light or numbered wall caught in a visible conflict receives a danger outline so the relationship is easy to inspect before you commit.
Play a Free Akari Game in Your Browser
If you are looking for an Akari game you can play free without installing anything, the Light Up (Akari) fixture runs directly in your browser on a fixed 5 by 5 board. The same puzzle is loaded every time you open the page, so you can compare attempts against a known target instead of guessing which version you got. Everything runs locally in the browser: no board state is sent to a server, no upload is performed, no account is required, and no daily download replaces the published fixture.
- Open the Light Up (Akari) page in any modern desktop or mobile browser; the 5 by 5 grid scales to fit the available width without losing its square shape.
- Tap a white cell to cycle it through clear, light, and X, or use the Arrow keys to move the active cursor and press B or Space to toggle a light and X for an empty mark.
- Place lights so every white cell ends up illuminated, no two lights share an unobstructed row or column, and every numbered wall counts exactly the right number of adjacent lights.
- Mark every one of the 20 white cells with either a light or an X before you check; leaving even one cell clear triggers an incomplete response and is not counted as a mistake.
- Choose Check board, or press Enter, to score the attempt; a strictly valid full board scores exactly 1,000 points immediately.
- If a full check returns invalid, read the highlighted conflicts and revise; a second invalid full check deadlocks the run and the puzzle must be Restarted to play again.
Touch and Keyboard Controls
The same board is fully playable with a mouse, a touchscreen, or a keyboard. On touch devices, tap a white cell to cycle it. On a desktop, you can either click cells the same way or drive a cursor through the grid with the Arrow keys. Moving the cursor onto a wall is allowed and follows a predictable rectangular path, but the placement controls are disabled on a wall so a stray key never plants a light on an illegal cell.
| Action | Touch or Mouse | Keyboard |
|---|---|---|
| Place or remove a light on the selected white cell | Tap or click until the cell shows a light | B or Space |
| Add or remove an X mark | Tap or click until the cell shows an X | X |
| Clear a marked white cell | Tap or click until the cell returns to clear | Delete or Backspace |
| Move the cursor through the grid | Click any cell | Arrow keys |
| Run a check | Choose Check board | Enter |
| Open or close the boss screen | Double-tap a shared gesture | Escape twice |
| Reset to a fresh puzzle | Choose Restart | Restart control only |
Lit cells receive a different surface treatment so coverage is visible without re-reading the lights list, and lights or numbered walls caught in a visible conflict receive a danger outline. Native button labels expose row, column, wall, clue, mark, and illumination terms to assistive technology, and the touch targets are sized so that drag gestures and hover-only states are never required. Everything runs locally, which means the same free Akari game behaves identically on a phone, a tablet, and a desktop without depending on a particular operating system.
Scoring, Checking, and the Restart Rule
The free Akari browser fixture scores with a deliberate, deterministic formula rather than a timer or streak counter. Checking is a manual step, never automatic, and it has three possible outcomes depending on what you have marked when you press Enter.
If even one white cell is still clear, the checker reports that the attempt is incomplete and does not count a mistake. This protects exploratory play, where you might want to test a partial placement before committing to the rest of the board. Once every one of the 20 white cells carries either a light or an X, the checker reconstructs the light set and applies every rule at once: lights must occupy white cells, no pair may share an unobstructed row or column, every numbered wall must have its exact orthogonal count, and every white cell must be illuminated. A strictly valid full board finishes immediately at exactly 1,000 points.
A full but invalid board records a single mistake and remains editable, so you can use the highlighted conflicts to revise without losing the run. A second invalid full check, however, deadlocks the puzzle and the run can only continue after a Restart. Both terminal states, completion and deadlock, are frozen, which means later clicks, key presses, cursor moves, and additional checks cannot alter the recorded outcome. Restart restores the authored clues, a clear 20-cell workspace, zero mistakes, zero score, and the initial cursor position. Completion time and the number of tentative marks do not influence the score, and the same fixture can be replayed without being randomized. The full rule set and the independent enumeration that produced the unique 5 by 5 answer are described in Simon Tatham's Light Up documentation.
Solving a 5 by 5 Akari Board
The published fixture holds 25 cells, with 20 white cells, four numbered walls, and one unnumbered wall, and its unique completed arrangement uses exactly five lights. The release test independently enumerates the constraint space under every rule to confirm that exactly one solution exists, so you can audit your own work against a known answer rather than a randomized board. Working the puzzle is easier if you tackle it in the order the rules actually constrain you.
Start with the numbered walls. For each clue, list the four orthogonal neighbors and ask which of them are still eligible to hold a light. A clue of 0 means all four neighbors must be X. A clue of 1 means exactly one neighbor is a light and the other three are X. A clue of 2 means exactly two neighbors are lights and the other two are X. Once you have written those requirements down, mark every neighbor that cannot host a light with an X, because X notes are personal and never block a beam. A useful shortcut is to notice that a clue of 1 with only one neighbor still able to host a light forces that neighbor to be lit.
Next, trace each dark corridor, which is a row or column of white cells bounded by walls. Every white cell in a corridor must be illuminated from inside the corridor, because a beam cannot cross a wall. Count how many white cells exist in that corridor; that is the minimum number of lights it must contain. If the count is one, the only cell in the corridor is forced to be a light. If the count is two, the two cells form a candidate pair, and you can immediately check whether placing both would create a mutual visibility conflict with a light in a perpendicular corridor. As you place candidates, keep re-reading the danger outlines; a light that sees another light across an open row is rejected as soon as both are placed.
Finally, run the Check board step only after every white cell is marked. The deterministic 1,000-point finish exists specifically so that a partial submission cannot accidentally lock in a low score, and so that a player who has understood the rules can audit the run against a known fixture. The cited Nikoli rules and Simon Tatham's Light Up documentation describe the same essential constraints, so the vocabulary you build on this 5 by 5 board transfers to larger Akari grids: numbered walls count only orthogonal neighbors, X marks do not block beams, and the unique answer is the one arrangement where every white cell is illuminated exactly once.