2048 · gemini-3.1-pro-preview

Output generated Cost / run $0.1455 (partial) Runtime 164.5s

Prompt for this run

Build a playable 2048 game using HTML elements and CSS with a 4 by 4 board. Use HTML, CSS, and JavaScript as needed. Write it to `index.html` in the current working directory using your file tools. Inline your own CSS and JavaScript. Do not use external assets, CDNs, or network requests. No third-party libraries are provided. Required behavior: - Arrow keys slide tiles toward the selected edge. Adjacent equal tiles merge once per tile per move, and the score increases by the value of each new merged tile. - For example, moving [2, 2, 2, 2] left produces [4, 4, 0, 0], not [8, 0, 0, 0]. Moving [2, 2, 4, 0] left produces [4, 4, 0, 0]. These examples describe the move before spawning a new tile. - Start with two tiles. After a move that changes the board, spawn exactly one tile in an empty cell: 2 with 90% probability, otherwise 4. Do not spawn after an unchanged move. - Animate movement and merging without allowing rapid input to corrupt board state. Prevent arrow keys from scrolling the page. - Show score, a win message on reaching 2048, and Game Over only when no valid move remains. Provide New Game to reset board and score; allow continuing after a win. Verify: Play a short sequence of arrow-key moves and check that tiles slide, a valid move adds a tile, and any observed merge updates the score by its merged value. Use New Game and check that the board returns to two tiles with a reset score.

⛨ sandboxed Open in new tab ↗

TAKE IT TO CODE

A single self-contained HTML file — copy it and open in any browser, or reuse the prompt with your own pi-agent run.

RUN

modelgemini-3.1-pro-preview

vendorGoogle

harnesspi 0.87.1 · browser iteration

generated2026-10-14

METRICS

runtime164.5s

tokens in233k (partial)

tokens out9.8k (partial)

cached163k (partial)

cost / run$0.1455 (partial)

Some OpenRouter billing records are unavailable. Cost and token totals are partial.

Transcript · 41 messages

system

user

assistant

thinking

**Designing the 2048 Game**

I'm starting with the bare bones: the HTML structure for a 4x4 grid. Next up, I'll flesh out the CSS for tile appearance and arrangement. I'm focusing on getting the basic tile sliding with arrow keys functional before implementing merge logic and scorekeeping.


**Refining Implementation Strategy**

I've decided to represent the game board as a 2D 4x4 integer array, which seems easier for tile movement logic. I've begun to code the spawning of the initial two tiles and the subsequent spawn after valid moves, with a 90/10 probability for a 2 or a 4. I'm focusing on animating the tile movements and mergers to make the UI look elegant. I've blocked out basic variables for score, game state (won/lost), and animation flags in the JavaScript implementation, including the basic HTML page.

→ write index.html (16753 bytes)

toolResult

Successfully wrote to index.html

assistant

thinking

→ browser {"text":"file:///tmp/job-AXY6e1/index.html","action":"goto"}

toolResult

Validation failed for tool "browser": - action: must be equal to constant - action: must be equal to constant - action: must be equal to constant - action: must be equal to constant - action: must be equal to constant - action: must be equal to constant - action: must be equal to constant - action: must be equal to constant Received arguments: { "text": "file:///tmp/job-AXY6e1/index.html", "action": "goto" }

assistant

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→ browser {"action":"screenshot"}

toolResult

Frame 1, +0ms

[Browser image supplied to model]

{"console":["warning: An iframe which has both allow-scripts and allow-same-origin for its sandbox attribute can escape its sandboxing."],"dom":"2048\nSCORE\n0\nNew Game\n4\n2","images":"attached"}

assistant

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**Analyzing Tile Display**

I've observed a display issue with the tile numbers, which seems to stem from the layout. After inspecting, I've identified that the tile `div` elements are using absolute positioning. I'm investigating how this impacts the visibility of the tile numbers and the overall rendering.

→ browser {"action":"type","text":"ArrowDown"}

toolResult

Frame 1, +0ms

[Browser image supplied to model]

{"console":["warning: An iframe which has both allow-scripts and allow-same-origin for its sandbox attribute can escape its sandboxing."],"dom":"2048\nSCORE\n0\nNew Game\n4\n2","images":"attached"}

assistant

thinking

**Examining Tile Behavior**

I'm now diving into the `index.html` file to understand the tile rendering and movement logic. Initial observation reveals some unexpected behavior; in the first image, the tiles were minuscule, and the second displayed (4 and 2) without apparent downward slide, but hold on - it seems they did actually slide. Need to verify within the code to be sure.


**Analyzing Key Bindings**

I'm now focusing on the key mapping implementation. The use of deprecated `e.keyCode` requires an update to `e.key`. I'm examining how this relates to tile initialization and positioning. I suspect a potential issue in the initial tile placement. It seems the animations, specifically the `appear` transition, might be interfering with the initial visibility, which can explain the tiny tile in the first image. I need to closely examine the CSS animation and the order of operations in tile creation.


**Investigating Movement Logic**

I'm now zeroing in on the tile movement logic, specifically why pressing ArrowDown didn't result in the 4 and 2 tiles sliding to the bottom. I've pinpointed the `buildTraversals(vec)` function as the culprit, and while I initially suspected an in-place array reversal, it seems the issue lies elsewhere. I'm going to step through this function with the debugger.

→ edit

{"edits":[{"newText":"    document.addEventListener('keydown', (e) => {\n        const keyMap = {\n            'ArrowUp': 0, 'w': 0, 'W': 0,

toolResult

Successfully replaced 1 block(s) in index.html.

assistant

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→ browser {"text":"file:///tmp/job-AXY6e1/index.html","action":"goto"}

toolResult

assistant

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→ browser {"text":"ArrowDown","action":"type"}

toolResult

Frame 1, +0ms

[Browser image supplied to model]

{"console":["warning: An iframe which has both allow-scripts and allow-same-origin for its sandbox attribute can escape its sandboxing."],"dom":"2048\nSCORE\n0\nNew Game\n4\n2","images":"attached"}

assistant

thinking

**Observing Render Updates**

I'm noticing a potential rendering delay, perhaps due to animations or `setTimeout`, causing me to miss the tile updates on the last frame. I'm testing the `ArrowDown` input and delaying it. It seems like using `e.key` is fixing the keydown issue.


**Analyzing Tile Movement**

I've carefully re-examined the images and confirmed the tiles haven't moved as expected after the "ArrowDown" input, specifically observing that "2" and "4" remain in the same positions. My focus has shifted to the `move(direction)` code. I'm now scrutinizing the `buildTraversals` function and questioning whether `Array.prototype.reverse` is unexpectedly mutating the array in-place, which would impact the expected tile movement logic.

→ browser {"y":200,"action":"click","x":200}

toolResult

Frame 1, +1ms

[Browser image supplied to model]

{"console":["warning: An iframe which has both allow-scripts and allow-same-origin for its sandbox attribute can escape its sandboxing."],"dom":"2048\nSCORE\n0\nNew Game\n4\n2","images":"attached"}

assistant

thinking

→ browser {"action":"type","text":"s"}

toolResult

Frame 1, +0ms

[Browser image supplied to model]

{"console":["warning: An iframe which has both allow-scripts and allow-same-origin for its sandbox attribute can escape its sandboxing."],"dom":"2048\nSCORE\n0\nNew Game\n4\n2","images":"attached"}

assistant

thinking

**Analyzing the Error Source**

I'm now investigating a potential event-handling issue, specifically concerning `e.key`. It appears this event is either not being captured by the browser, or maybe the grid is failing to render. I also see an inconsistency between the image results, where a 4 and 2 are in different places to a previous image, but previously, the 4 and 2 were in the same positions.

→ browser {"action":"evaluate","text":"move(2);"}

toolResult

assistant

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→ browser {"action":"screenshot"}

toolResult

Frame 1, +0ms

[Browser image supplied to model]

{"console":["warning: An iframe which has both allow-scripts and allow-same-origin for its sandbox attribute can escape its sandboxing."],"dom":"2048\nSCORE\n0\nNew Game\n4\n2","images":"attached"}

assistant

thinking

**Analyzing Movement Logic**

I'm trying to figure out why the tiles aren't shifting downwards as expected. I just checked the execution of `move(2);` and am now investigating the internal `move` logic. I think there might be a focus issue to debug.

→ browser {"text":"isAnimating","action":"evaluate"}

toolResult

assistant

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→ browser {"action":"evaluate","text":"move(3)"}

toolResult

assistant

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→ browser {"action":"screenshot"}

toolResult

Frame 1, +0ms

[Browser image supplied to model]

{"console":["warning: An iframe which has both allow-scripts and allow-same-origin for its sandbox attribute can escape its sandboxing."],"dom":"2048\nSCORE\n0\nNew Game\n4\n2","images":"attached"}

assistant

thinking

**Examining Functionality Failure**

I'm now zeroing in on the `move` function, specifically the nested loops. The logic for accessing the `board` within those loops looks sound superficially, but I need to make sure that the conditionals are correct to avoid accessing bad memory. I am going to see if any index of the `r` or `c` variables is out of bound.

**Pinpointing Potential Issues**

I've hit a potential snag with `setTimeout` and `isAnimating` potentially blocking indefinitely. I need to make sure those two interact as expected, and I'm now looking into how `buildTraversals` is influencing that interaction, particularly the reversal logic based on the direction vector. I'm also double checking if `findFarthestPosition` might be the root cause of the error.

**Analyzing Animation Control**

I see a critical error: `isAnimating` was not always being reset correctly. Specifically, if a move was attempted but no tiles actually moved, `isAnimating` was still set to `true`, blocking further moves. The `else` clause now resets `isAnimating` appropriately in the original code, but I need to make sure this fix is properly applied!

**Verifying Bound Checks**

I'm now tracing the logic where a `tile` exists and examining the potential for out-of-bounds array access within `findFarthestPosition`. Specifically, I'm verifying that if a row index goes out of bounds, I appropriately handle it so that it will not cause an error when checking the `board` index with `board[r]?.[c]`. Then I am reviewing what happens when the `next` value is checked to see if it is valid. Finally, I will check the movement conditions and ensure valid board index writes.

→ browser {"text":"board","action":"evaluate"}

toolResult

assistant

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→ browser {"text":"JSON.stringify(board)","action":"evaluate"}

toolResult

assistant

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→ browser {"action":"evaluate","text":"JSON.stringify(tiles)"}

toolResult

Validation failed for tool "browser": - action: must be equal to constant - action: must be equal to constant - action: must be equal to constant - action: must be equal to constant - action: must be equal to constant - action: must be equal to constant - action: must be equal to constant - action: must be equal to constant Received arguments: { "action": "evaluate", "text": "JSON.stringify(tiles)" }

assistant

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→ browser {"action":"evaluate","text":"score"}

toolResult

assistant

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→ browser {"action":"evaluate","text":"isAnimating"}

toolResult

assistant