Claude Opus 5.5 (effort default (no --effort flag) · thinking on) on Fix a cron next-fire-time calculator (steps, names, macros, day-of-month OR day-of-week, leap days, strict validation)

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

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Estimated cost: $0.21
Wall time: 51s
Human step-ins: 0
Outcome: Pass

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# Task: fix the cron schedule calculator `cron.py` has a function `next_fire(expr, after)` that should return the next time a cron schedule fires, but it gets many schedules wrong and is too slow for rare schedules. Fix it (rewrite freely) so it follows every rule below exactly. Python standard library only. Keep the function name and signature. No network. ## Rules 1. `expr` has exactly 5 whitespace-separated fields: minute (0-59), hour (0-23), day-of-month (1-31), month (1-12), day-of-week (0-7, where both 0 and 7 mean Sunday, 1 = Monday ... 6 = Saturday). Leading/trailing whitespace and multiple spaces between fields are allowed. 2. Each field is a comma-separated list of items. An item is `*`, a number `n`, a range `a-b` (inclusive, requires a <= b), or any of those followed by `/step` (step >= 1): `*/s` = every s-th value starting at the field minimum, `a-b/s` = a, a+s, ... up to b, and `a/s` = a, a+s, ... up to the field maximum. 3. Month names `JAN`-`DEC` and day names `SUN`-`SAT` may be used anywhere a number may be used in the month and day-of-week fields (including in ranges, e.g. `MON-FRI`), case-insensitive. 4. Macros (case-insensitive) replace the whole expression: `@yearly` and `@annually` = `0 0 1 1 *`, `@monthly` = `0 0 1 * *`, `@weekly` = `0 0 * * 0`, `@daily` and `@midnight` = `0 0 * * *`, `@hourly` = `0 * * * *`. 5. Day matching: if BOTH day-of-month and day-of-week are restricted (the field text is not exactly `*`), a day matches when EITHER field matches. If only one of them is restricted, only that one counts. A field like `*/1` or `1-31` counts as restricted. 6. `after` is a naive `datetime`. Return the earliest matching minute STRICTLY after `after`, as a naive `datetime` with seconds and microseconds 0. (If `after` is 10:00:30 and the schedule fires every minute, the answer is 10:01:00.) No time zones, no DST: treat times as plain calendar times. 7. Raise `ValueError` for: wrong number of fields, unknown macro, any value outside the field's range, `a > b` in a range, step 0 or a non-numeric step, empty items (e.g. `1,,2`), unknown names, or any other unparsable text. 8. If the schedule can never fire within 5 years after `after` (e.g. `0 0 31 2 *`), raise `ValueError` instead of looping forever. A schedule that fires only on 29 February must still be found (it is at most ~4 years away). 9. Every call must return (or raise) within 1 second on an ordinary machine, including the leap-day case. The grader runs a hidden unittest suite that checks exactly these rules.

The starting code ANDs day fields, ignores names/macros/7=Sunday, is inclusive of 'after', accepts invalid fields and scans minute by minute (too slow / never terminates for rare schedules). Each rule has exact expected datetimes. 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. All 8 hidden unittest cases pass (strictly-after semantics, lists/ranges/steps incl. a/s, month/day names, 0 and 7 = Sunday, macros, DOM/DOW OR rule incl. */1 as restricted, 18 invalid expressions raise ValueError, never-firing schedule raises within 1 s, 29 Feb found within 1 s).

Setup notes: Use Case Scout batch 7 case g01-cron-next-fire (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. Claude Code's own reported cost for claude-opus-5.5: $0.211146. Score: 8/8. 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: $0.21
Wall time: 51s
Human step-ins: 0
Turns: 5

Model usage
Model	Input tok	Output tok	Cost
AClaude Opus 5.5anthropic/claude-opus-5.5effort default (no --effort flag) · thinking on	106,540	4,904	$0.21

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. All 8 hidden unittest cases pass (strictly-after semantics, lists/ranges/steps incl. a/s, month/day names, 0 and 7 = Sunday, macros, DOM/DOW OR rule incl. */1 as restricted, 18 invalid expressions raise ValueError, never-firing schedule raises within 1 s, 29 Feb found within 1 s).
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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  "result": "I rewrote `cron.py`. `next_fire(expr, after)` keeps its name and signature and now follows all nine rules. It uses only the standard library.\n\nI checked it against a slow minute-by-minute reference on 270 random cases across nine different expressions, and all of them matched. I also ran a set of targeted checks, which all passed:\n- **Strictly after:** `* * * * *` at 10:00:30 returns 10:01:00.\n- **Leap day:** `0 0 29 2 *` from 2024-03-01 finds 2028-02-29.\n- **Impossible schedule:** `0 0 31 2 *` raises `ValueError` in under 1 ms.\n- **Day matching:** `0 0 29 2 1` uses the \"either field\" rule and fires on the first Monday in February.\n- **Sunday as 7:** `* * * * 7` is treated the same as Sunday (0).\n- **Formatting:** names, macros, mixed case, and extra spaces all parse correctly.\n- **Invalid input:** each type of bad expression in rule 7 raises `ValueError`.\n\n**How it works:**\n- **Speed:** instead of stepping through every minute, it checks one day at a time for up to 5 years and then picks the first matching hour and minute on that day. Even the slowest cases finish in about a millisecond.\n- **Stricter parsing:** numbers must be plain digits, so things like `+5` are rejected. Names are only accepted in the month and day-of-week fields, and `@` macros are recognised after stripping surrounding whitespace.\n\n**Three behaviours you might not expect:**\n- **`SAT-SUN` is rejected.** Sunday is 0, so the range runs backwards and is an error under rule 7. Use `SAT,SUN` instead.\n- **Steps can include Sunday as 7.** The day-of-week field runs from 0 to 7, so a step such as `1/3` produces 1, 4 and 7, and 7 counts as Sunday.\n- **Leap days can be more than 5 years apart.** 2100 is not a leap year, so a 29 February schedule starting from 2097 would next fire in 2104. Rule 8 says to raise `ValueError` in that case, and the code does.",
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