Claude Haiku 5.5 (effort default (no --effort flag) · thinking on) on Make invoice maths exact: half-up line rounding, per-rate VAT, largest-remainder allocation, banker's FX rounding

AClaude Haiku 5.5default · thinking on · Claude Code 2.1.299 (headless -p) · cloud · 2026-10-17 · by @bobsiopener

Trust 80%Fully autonomoussuccess · first tryCompare

Estimated cost: $0.0070
Wall time: 30s
Human step-ins: 0
Outcome: Pass

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Exact prompt

# Task: make the invoice maths exact `money.py` uses binary floats and produces off-by-a-cent results. Fix it so these rules hold exactly (inputs and outputs are decimal strings; keep the function names and signatures): **All functions:** every returned amount is a string with exactly the target currency's decimals (e.g. "0.00", "-1.50", "1200" for JPY, "1.001" for BHD). Never output a negative zero such as "-0.00": a zero is always unsigned. `currency`/`to_currency` default to EUR where shown. **invoice(lines, currency)** - Line net = price x qty x (1 - discount_pct/100), rounded **half-up** (away from zero on .5) to the currency's decimals (EUR/USD 2, JPY 0, BHD 3). `qty` may be fractional, `discount_pct` is optional (default 0). Negative prices (credit lines) are allowed: half-up means 0.5 rounds away from zero for them too. - `net` = sum of rounded line nets. VAT is computed **per VAT rate** on that rate's summed rounded nets and rounded half-up. `vat` maps each rate string exactly as given (e.g. "20", "5.5") to its amount, in first-appearance order. `gross` = net + sum of VAT amounts. **allocate(amount, weights, currency)** - Split `amount` in proportion to non-negative integer `weights` (at least one positive) so that the parts sum **exactly** to amount: floor each exact share to the smallest unit (toward negative infinity for negative amounts — i.e. compute on the absolute value and re-apply the sign), then hand out remaining smallest units one each to the parts with the largest remainders; ties (equal remainders) go to the lower index. Example: `allocate("0.05", [3, 7])` -> `["0.02", "0.03"]` (exact shares 1.5 and 3.5 cents, equal remainders, the extra cent goes to index 0). Zero weight gets zero. Raise `ValueError` if all weights are 0. **convert(amount, rate, to_currency)** - amount x rate, rounded **half-even** (banker's) to the target decimals. Standard library only. No network.

Float classics (1.005, 2.675), half-up for negatives, VAT on grouped rounded nets, -0.00 suppression, 0/2/3-decimal currencies, deterministic largest-remainder tie-breaks and half-even conversion all have exact expected strings. 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 9 hidden unittest cases pass: half-up line rounding incl. float traps, discount + fractional qty, VAT grouping and order, credit lines and no '-0.00', JPY/BHD decimals, empty invoice, allocation (ties, zero weights, negatives, ValueError), allocation sums exactly, half-even conversion.

Setup notes: Use Case Scout batch 6 case f04-money-precision (offline fixture). Prepared with batch6/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-haiku-5.5: $0.006982. Score: 9/9. 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: $0.0070
Wall time: 30s
Human step-ins: 0
Turns: 5

Model usage
Model	Input tok	Output tok	Cost
AClaude Haiku 5.5anthropic/claude-haiku-5.5effort default (no --effort flag) · thinking on	115,087	6,351	$0.0070

Reproduce this run

Use the use case prompt on the use case page.
Same setup: Claude Haiku 5.5 (anthropic/claude-haiku-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 9 hidden unittest cases pass: half-up line rounding incl. float traps, discount + fractional qty, VAT grouping and order, credit lines and no '-0.00', JPY/BHD decimals, empty invoice, allocation (ties, zero weights, negatives, ValueError), allocation sums exactly, half-even conversion.
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 `money.py` so every rule in the spec is computed exactly. I ran the spec examples and some edge cases by hand; I did not add a test file, and the directory has no existing tests.\n\nWhat changed:\n- **Exact arithmetic:** inputs are parsed with `Fraction`, so binary float error is gone. Rounding happens only at the points the spec names, in integer minor units.\n- **Rounding:** `invoice` and `allocate` use half-up, computed on the absolute value so it works for negatives. `convert` uses Python's `round()` on a `Fraction`, which is half-even.\n- **Formatting:** one helper formats minor units to the currency's decimals and never emits a sign for zero, so \"-0.00\" cannot appear.\n- **Signatures:** unchanged. The `currency=\"EUR\"` defaults on `invoice` and `allocate` are kept, and `convert` still has no default.\n\nChecks run:\n- `allocate(\"0.05\", [3, 7])` gives `['0.02', '0.03']`, and the negative case mirrors it.\n- `allocate(\"10.00\", [1, 1, 1])` gives `['3.34', '3.33', '3.33']`.\n- `invoice` with price \"2.675\", qty 3, 10% discount, VAT 20 gives net \"7.22\", VAT \"1.44\", gross \"8.66\".\n- Credit lines of \u00b10.005 net to \"0.00\" with no negative zero.\n- The BHD example `1.0005` rounds to \"1.001\".\n- `convert(\"0.125\")` gives \"0.12\" and `convert(\"0.135\")` gives \"0.14\".\n\nChoices I made where the spec was silent:\n- `allocate` raises `ValueError` if `amount` has more decimals than the currency allows, since the parts could not sum exactly to it.\n- `allocate` raises `ValueError` for negative or non-integer weights, not just for all-zero weights.\n- VAT rate keys are used as given, so \"20\" and \"20.0\" would be two separate entries.",
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