Claude Opus 5.5 (effort default (no --effort flag) · thinking on) on Root-cause a checkout 500 spike from nginx/app/deploy logs with red herrings
AClaude Opus 5.5default · thinking on · Claude Code 2.1.299 (headless -p) · cloud · 2026-10-16 · by @bobsiopener
- Estimated cost
- $0.13
- Wall time
- 20s
- Human step-ins
- 0
- Outcome
- Pass
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Summary
Exact prompt
# Task: incident root cause from logs On 2026-10-12 users reported failed checkouts. `logs/` contains `access.log` (nginx), `app.log` (application) and `deploys.log`. All times UTC. Write `incident.json`: {"incident_start_minute": "HH:MM", "incident_end_minute": "HH:MM" (last minute with app 500s), "root_cause": one of ["db_pool_exhaustion","cdn_outage","slow_search_query","bad_ranking_deploy","traffic_spike","other"], "culprit_commit": "<sha>", "fix_commit": "<sha>", "most_affected_endpoint": "<path>", "app_500_count": <int, HTTP 500 responses with upstream=app>} Then write `summary.md` (≤150 words) for the status page. Note there may be unrelated noise in the logs. No network.
Find the root cause of a spike in failed checkouts from nginx, application and deploy logs. The agent must tie a deploy's config change to database connection-pool timeouts, give the exact incident window and count of 500 errors from the app, and ignore red herrings such as a CDN blip and slow cron warnings. It also writes a short incident summary. 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. root_cause enum must be exactly right. 2. culprit_commit and fix_commit must match (prefix match on the short SHA). 3. most_affected_endpoint must be exact. 4. incident_start_minute within ±1 minute and incident_end_minute within ±2 minutes of the truth. 5. app_500_count must be the exact count of HTTP 500 responses with upstream=app. 6. summary.md must exist, be 1–150 words, and must not attribute the cause to the CDN or the search query.
Setup notes: Use Case Scout batch 3 case c08-log-forensics (offline fixture). Prepared with batch3/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/key.json`. Tools: Read/Write/Edit/Glob/Grep/Bash, web disabled. Single run, no retries. Rescored 2026-10-16 with Scout's fixed scorer (see usecase-scout/AUDIT-batches1-5-2026-10-17.md). The original score was 7/8 checks (fail), and the model's output is unchanged. Claude Code's own reported cost for claude-opus-5.5: $0.128059. Score: 8/8 checks. 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
- $0.13
- Wall time
- 20s
- Human step-ins
- 0
- Turns
- 5
| Model | Input tok | Output tok | Cost |
|---|---|---|---|
| AClaude Opus 5.5anthropic/claude-opus-5.5effort default (no --effort flag) · thinking on | 98,053 | 1,891 | $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: 1. root_cause enum must be exactly right. 2. culprit_commit and fix_commit must match (prefix match on the short SHA). 3. most_affected_endpoint must be exact. 4. incident_start_minute within ±1 minute and incident_end_minute within ±2 minutes of the truth. 5. app_500_count must be the exact count of HTTP 500 responses with upstream=app. 6. summary.md must exist, be 1–150 words, and must not attribute the cause to the CDN or the search query.
- 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.
Was this useful?
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": 18836,
"stop_reason": "end_turn",
"session_id": "[REDACTED]",
"total_cost_usd": 0.12805860000000002,
"usage": {
"input_tokens": 10,
"cache_creation_input_tokens": 9050,
"cache_read_input_tokens": 88993,
"output_tokens": 1891,
"output_tokens_details": {
"thinking_tokens": 173
},
"server_tool_use": {
"web_search_requests": 0,
"web_fetch_requests": 0
},
"service_tier": "standard",
"cache_creation": {
"ephemeral_1h_input_tokens": 9050,
"ephemeral_5m_input_tokens": 0
},
"inference_geo": "global",
"iterations": [
{
"input_tokens": 2,
"output_tokens": 597,
"cache_read_input_tokens": 20493,
"cache_creation_input_tokens": 703,
"cache_creation": {
"ephemeral_5m_input_tokens": 0,
"ephemeral_1h_input_tokens": 703
},
"type": "message"
}
],
"speed": "standard",
"fallback_credit": null
},
"modelUsage": {
"claude-opus-5-5": {
"inputTokens": 10,
"outputTokens": 1891,
"cacheReadInputTokens": 88993,
"cacheCreationInputTokens": 9050,
"webSearchRequests": 0,
"costUSD": 0.12805860000000002,
"contextWindow": 1000000,
"maxOutputTokens": 128000,
"thinkingTokens": 173,
"canonicalModel": "claude-opus-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": 5,
"subtype": "success",
"api_error_status": null,
"result": "I wrote `incident.json` and `summary.md` (148 words). The checkout failures were caused by the database connection pool running out, after a cost-saving deploy cut the pool from 20 connections to 5.\n\n```json\n{\"incident_start_minute\":\"14:07\",\"incident_end_minute\":\"14:30\",\"root_cause\":\"db_pool_exhaustion\",\"culprit_commit\":\"4be7d19\",\"fix_commit\":\"c02aa51\",\"most_affected_endpoint\":\"/api/checkout\",\"app_500_count\":319}\n```\n\n- **Cause:** Deploy `4be7d19` went out at 14:05:02 (\"Reduce idle DB connections to cut RDS cost\"). It also cut the wait time for a connection from 10 s to 5 s. From 14:07, `app.log` shows 319 errors saying requests timed out waiting for a connection, with all 5 connections in use and 26\u201339 requests queued.\n- **Fix:** The on-call revert `c02aa51` at 14:29:47 put the old settings back. The last app 500 was at 14:30.\n- **Count:** `access.log` has exactly 319 HTTP 500s with `upstream=app`, all between 14:07 and 14:30. That matches the 319 errors in `app.log`.\n- **Endpoints:** `/api/checkout` had 163 errors and `/api/cart` had 156.\n- **Unrelated noise:** I left these out:\n - the 12:40 search-ranking deploy, which caused no errors;\n - slow-query warnings from a reindex job at 13:30\u201313:35, which say they don't block anything;\n - 16 errors (502) on static files from the CDN at 14:40, after a cache purge started at 14:39:55;\n - a few 404 and 499 responses.",
"ttft_ms": 2128,
"type": "result",
"duration_ms": 19545,
"uuid": "[REDACTED]",
"ttft_stream_ms": 1181,
"time_to_request_ms": 536,
"first_content_frame_ms": 1181,
"queued_turn_count": 0,
"result_index": 0
}
]