Claude Opus 5.5 (effort default (no --effort flag) · thinking on) on Animate a row of pendulums, each swinging at its own true period, in one self-contained HTML file

AClaude Opus 5.5default · thinking on · Claude Code 2.1.299 (headless -p) · cloud · 2026-10-23 · by @bobsiopener

Trust 80%Fully autonomoussuccess · first tryCompare

Estimated cost: $0.13
Wall time: 23s
Human step-ins: 0
Outcome: Pass

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Exact prompt

# Animate a row of pendulums, each swinging at its own true period, in one self-contained HTML file Make a small animated scene: a pendulum wave. Write one file, `out/scene.html`, that works opened straight from disk with no network access. `spec.json` gives the page title, the stage size and the scene parameters. **Looks are not scored**: the page is opened in a headless browser (800x600 window, UTC time zone, network blocked) and checked by objective tests only. ## Scene contract - Draw the scene on one `<canvas>` or `<svg>` stage of `width` x `height` CSS pixels (spec.json), visible on load, with `<title>` containing spec.json `title`. - Animate continuously from load (`requestAnimationFrame` or timers); no click is needed unless stated below. - Expose `window.sceneState()`, returning the scene's current state in stage pixel coordinates (origin top-left of the stage): `{pendulums: [{name, angle_deg, pivot: {x, y}, bob: {x, y}}, ...]}`. Extra fields are fine. It must describe what is actually drawn. - Each pendulum in spec.json has a `length_m`. Its period T is the time for one full back-and-forth swing of an ideal small-angle pendulum of that length under `gravity` (m/s²); every pendulum swings with the same amplitude `amplitude_deg`. `sceneState()` must return the state at the moment it is called (work it out from `performance.now()`, don't return the last frame's numbers). - The page must log no errors and throw no exceptions. Keep the file at most 200,000 bytes; no external scripts, fonts, images or URLs (inline everything). ## Checks (partial credit = share passed) 1. `self_contained`: `out/scene.html` exists, is at most 200,000 bytes, references no http(s) or protocol-relative URL, and requests nothing from the network when opened. 2. `has_canvas_or_svg`: a visible `<canvas>` or `<svg>` of at least 300x200 CSS pixels is on the page. 3. `frames_change`: over 3 s, some later screenshot differs from the first in at least 0.1% of pixels, and at least 3 of 30 screenshots differ. 4. `swing_periods`: `sceneState().pendulums` names exactly the pendulums in spec.json, and over 3 s each pendulum's `angle_deg` stays within 2.5° of `amplitude_deg` × cos(2π t / T + φ) for some fixed φ, where t is `performance.now()` in seconds and T is the pendulum's period. 5. `bobs_on_strings`: in every sample, each bob is within 3 px of pivot + `length_m` × `px_per_m` × (sin θ, cos θ), θ = `angle_deg` (positive swings the bob to the right of the pivot, y grows downwards). 6. `no_console_errors`: no uncaught exception, `console.error` or browser error is logged during the run. ## How this run works - Work on your own: nobody will answer questions in this task, and writing to `ask/` counts against the run. - Write only under `out/`. Create `out/` if it is missing. Inputs are synthetic; don't fetch anything from the network. - Scoring is partial credit: each listed check is pass/fail, and the score is the share passed. Numbers are compared to within 0.005 unless the task says otherwise.

Make a pendulum wave animation as one self-contained HTML file. A headless browser checks objective facts only: the file is offline and small, a canvas or SVG stage is drawn, frames change, the scene follows a timed specification (swing periods; bobs on strings) and nothing errors. A poster PNG and a short MP4 are captured for the gallery. Looks are not scored. Original benchmark task written for usecaserank.com (not based on a specific public post). Headless, offline run on a reproducible fixture. Each run's notes say how its cost was measured (estimates are marked).

Success criteria: self_contained has_canvas_or_svg frames_change swing_periods bobs_on_strings no_console_errors

Setup notes: Batch 29 case h07-pendulum-wave (offline, synthetic inputs, seed 2475531774). Autonomous case: no stand-in user and no step-ins expected; any file the solver wrote to ask/ is counted as a measured intervention (0) and blocks a pass. Prompt = TASK.md verbatim. Hidden key kept outside the solver's work dir. Scored with the case's scorer (python3 score.py WORKDIR KEYDIR, absolute paths); pass = every check true and no ask/ files. Tools: Read/Write/Edit/Glob/Grep/Bash, web disabled. Single run, no retries. 1-min load average at scoring 0.37 (8 cores). Creative case: looks are not scored; objective checks run in headless google-chrome (800x600, UTC, network blocked, Date mocked). Gallery media (3 s capture: poster.png + clip.mp4) written by the scorer to a fresh MEDIA_DIR per run (media/<run>/), SHA-256 in evidence.media; a single failed scene check is rescored once (both recorded in rescore). Time-zone results depend on the system time-zone database: tzdata 2026c-0+deb13u1 (Python zoneinfo). Claude Code's own reported cost for claude-opus-5.5: $0.133583. Score: 6/6. Cost is an ESTIMATE: measured tokens x pricing.json list price (Claude Pro subscription, nothing billed); input_tokens include cache reads and writes. Single run.

Estimated cost List-price estimate; not actually billed.

Output

Metrics

Estimated cost: $0.13
Wall time: 23s
Human step-ins: 0
Turns: 4

Model usage
Model	Input tok	Output tok	Cost
AClaude Opus 5.5anthropic/claude-opus-5.5effort default (no --effort flag) · thinking on	79,001	2,440	$0.13

Reproduce this run

Use the use case prompt on the use case page.
Same setup: Claude Opus 5.5 (anthropic/claude-opus-5.5, effort default (no --effort flag) · thinking on) via Claude Code 2.1.299 (headless -p), cloud.
It counts as a success only if it meets every success criterion: self_contained has_canvas_or_svg frames_change swing_periods bobs_on_strings no_console_errors
Log model, tokens, wall time, human step-ins and the evidence log, then submit it as a reproduction. A different model? Submit a head-to-head rerun.

How runs are scored: Methodology.

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Automated checks

Trust 80% comes from these checks (how Trust % works).

Run date is not in the future : passed
Model is in the dated pricing table : passed
Cost recomputed from tokens matches : passed
Cached tokens are consistent : passed
Output throughput is plausible : passed
Autonomy matches step-ins : passed
Step-ins do not exceed turns : passed
Retries agree with first-try result : passed
Evidence log SHA-256 matches : passed
Evidence log is substantial : passed

Evidence log

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    "canonicalModel": "claude-opus-5-5",
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  "permission_denials": [],
  "terminal_reason": "completed",
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  "subagent_stats": {
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  "result": "I wrote `out/scene.html`. I opened it once in headless Chrome and it ran: `sceneState()` returned all three pendulums (P1, P2, P3) with sensible angles and bob positions. I did not run the six graded checks themselves. That means no 3-second sampling against the cosine formula, no screenshot comparison, and no console-error capture.\n\n- **Stage:** one 700\u00d7450 canvas, titled \"Pendulum Wave 706\", with the three pendulums hanging from a bar 40 px from the top.\n- **Swing:** each angle is calculated directly from `performance.now()` as `12\u00b0 \u00d7 cos(2\u03c0t / T)`, where `T = 2\u03c0\u221a(L/g)`. Every pendulum starts at the same phase. This gives periods of about 1.79 s for P1, 1.27 s for P2 and 1.00 s for P3.\n- **`sceneState()`:** works out the state fresh each time it's called rather than reusing the last frame. The drawing code uses the same calculation, so the bobs on screen sit at the reported positions. Each bob is placed exactly at pivot + L \u00d7 300 px \u00d7 (sin \u03b8, cos \u03b8).\n- **Self-contained:** the scene values from `spec.json` are written into the script, with no external files, fonts or URLs. Animation uses `requestAnimationFrame` and starts on load.\n\nBecause the values are copied in, changing `spec.json` won't change the page; the file would need regenerating.",
  "ttft_ms": 1467,
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 }
]