Claude Sonnet 5.5 (effort default (no --effort flag) · thinking on) on Make a Node.js JSON Patch module correct (no input mutation, pointer escaping, array index rules, move-into-child, deep test, error codes)

AClaude Sonnet 5.5default · thinking on · Claude Code 2.1.299 (headless -p) · cloud · 2026-10-19 · by @bobsiopener

Trust 80%Fully autonomoussuccess · first tryCompare

Estimated cost: $0.09
Wall time: 35s
Human step-ins: 0
Outcome: Pass

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Exact prompt

# Task: make the JSON Patch module correct `patch.js` (CommonJS, Node.js 20) exports `apply(doc, ops)` and `PatchError`. It applies a JSON Patch (a list of operations) to a JSON document, but it mutates its inputs, mishandles pointers and array indexes, and throws inconsistent errors. Fix it (rewrite freely) so it implements `PATCH_SPEC.md` exactly. No dependencies beyond Node.js 20 built-ins; no network. Keep the exports. The grader runs a hidden `node --test` suite against your `patch.js`. If you add your own tests in a `test/` folder they must pass too (`node --test test/`).

The starting module mutates inputs, has no error codes, treats inherited properties as present (prototype pollution via __proto__), mishandles '-', leading zeros and out-of-range indexes, and uses shallow ===. Every case asserts an exact result or (code, index). 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: 1. hidden_tests_pass: all 11 hidden node:test cases pass. 2. own_tests_pass_or_absent: the agent's test/ (if any) passes.

Setup notes: Use Case Scout batch 7 case g11-js-json-patch (offline fixture). Prepared with batch7/prepare.sh; hidden key/tests kept outside the agent's work dir. Prompt = TASK.md verbatim. Scored with the scout's scorer: `python score.py WORKDIR KEYDIR`. Tools: Read/Write/Edit/Glob/Grep/Bash, web disabled. Single run, no retries. 1-min load average at scoring: 1.27. Claude Code's own reported cost for claude-sonnet-5.5: $0.093646. Score: 11/11. 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.

Metrics

Estimated cost: $0.09
Wall time: 35s
Human step-ins: 0
Turns: 3

Model usage
Model	Input tok	Output tok	Cost
AClaude Sonnet 5.5anthropic/claude-sonnet-5.5effort default (no --effort flag) · thinking on	61,911	4,321	$0.09

Reproduce this run

Use the use case prompt on the use case page.
Same setup: Claude Sonnet 5.5 (anthropic/claude-sonnet-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: 1. hidden_tests_pass: all 11 hidden node:test cases pass. 2. own_tests_pass_or_absent: the agent's test/ (if any) passes.
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

[
 {
  "duration_api_ms": 33980,
  "stop_reason": "end_turn",
  "session_id": "[REDACTED]",
  "total_cost_usd": 0.0936463,
  "usage": {
   "input_tokens": 6,
   "cache_creation_input_tokens": 11342,
   "cache_read_input_tokens": 50563,
   "output_tokens": 4321,
   "output_tokens_details": {
    "thinking_tokens": 1110
   },
   "server_tool_use": {
    "web_search_requests": 0,
    "web_fetch_requests": 0
   },
   "service_tier": "standard",
   "cache_creation": {
    "ephemeral_1h_input_tokens": 11342,
    "ephemeral_5m_input_tokens": 0
   },
   "inference_geo": "global",
   "iterations": [
    {
     "input_tokens": 2,
     "output_tokens": 409,
     "cache_read_input_tokens": 19948,
     "cache_creation_input_tokens": 3933,
     "cache_creation": {
      "ephemeral_5m_input_tokens": 0,
      "ephemeral_1h_input_tokens": 3933
     },
     "type": "message"
    }
   ],
   "speed": "standard",
   "fallback_credit": null
  },
  "modelUsage": {
   "claude-sonnet-5-5": {
    "inputTokens": 6,
    "outputTokens": 4321,
    "cacheReadInputTokens": 50563,
    "cacheCreationInputTokens": 11342,
    "webSearchRequests": 0,
    "costUSD": 0.0936463,
    "contextWindow": 1000000,
    "maxOutputTokens": 128000,
    "thinkingTokens": 1110,
    "canonicalModel": "claude-sonnet-5-5",
    "provider": "firstParty",
    "costBasis": "list"
   }
  },
  "permission_denials": [],
  "terminal_reason": "completed",
  "fast_mode_state": "off",
  "fast_mode_disabled_reason": "sdk_opt_in_required",
  "subagent_stats": {
   "spawned": 0,
   "requested": {
    "background": 0,
    "foreground": 0,
    "unset": 0
   },
   "started_in_background": 0,
   "max_depth": 0,
   "spawned_by_subagents": 0,
   "completed": 0,
   "failed": 0,
   "killed": {
    "parent": 0,
    "user": 0,
    "system": 0
   },
   "refused": {
    "depth_limit": 0,
    "concurrency_limit": 0,
    "budget": 0
   },
   "by_type": {}
  },
  "safety_stops": 0,
  "is_error": false,
  "num_turns": 3,
  "subtype": "success",
  "api_error_status": null,
  "result": "I rewrote `patch.js` to follow `PATCH_SPEC.md`. I only ran a quick smoke check by hand and did not write any tests under `test/`.\n\nThe smoke check covered these cases, and all behaved as the spec says:\n- **Inputs:** the original `doc` was unchanged after an `add`, `move` and `copy` sequence.\n- **`__proto__`:** moving a value to `/b/__proto__` created an ordinary own member.\n- **Errors:** I checked one case each for:\n  - an `add` index past the array length (`BAD_INDEX`);\n  - a `move` into its own child (`MOVE_INTO_CHILD`);\n  - a `test` on an inherited name like `constructor` (`PATH_NOT_FOUND`);\n  - an index with a leading zero (`BAD_INDEX`).\n\nThe module works on a deep copy of `doc` and deep-copies every inserted `value`, so the result shares nothing with the inputs. A failure discards the copy, so nothing changes. `PatchError` has `code` and `index`, and both exports are kept.\n\nThe spec doesn't say what `remove` with path `\"\"` should return. I made it return `null`. If the hidden tests expect something else, that is the line to change.",
  "ttft_ms": 2023,
  "type": "result",
  "duration_ms": 34472,
  "uuid": "[REDACTED]",
  "ttft_stream_ms": 1229,
  "time_to_request_ms": 276,
  "first_content_frame_ms": 1230,
  "queued_turn_count": 0,
  "result_index": 0
 }
]