True Token Ledger

A token counter counts tokens. An invoice charges for billing events. Anthropic prices a 5-minute cache write at 1.25x base input, a 1-HOUR cache write at 2x, and a cache read at 0.1x -- so a dashboard that multiplies a raw count by a base rate is wrong in both directions at once, and it never throws. It looks entirely healthy until the invoice arrives.

THE SECOND TRAP IS WORSE BECAUSE IT LOOKS LIKE ARITHMETIC. input_tokens EXCLUDES tokens read from or written to the cache -- documented as "input tokens which were not read from or used to create a cache". The real total is cache_read + cache_creation + input. Code that adds the cache fields to a total it believes already includes them double-counts; code that reads input_tokens alone under-counts enormously on exactly the workloads where caching matters. Both produce a plausible number.

THE 1-HOUR TIER IS THE ONE EVERYONE MISSES. This listing was specced with a single 1.25x multiplier. Checking Anthropic’s documentation before encoding it surfaced the second tier; building to the spec as written would have under-reported 1-hour writes by 37.5% -- the exact silent under-reporting the product exists to detect.

IT REFUSES TO PRICE A MODEL IT DOES NOT KNOW, throwing rather than returning zero. Zero would make an unpriced model look free: the same silent under-reporting, introduced by the tool meant to catch it.

MONEY IS INTEGER PICODOLLARS IN BIGINT. A ledger accumulates, and float drift compounds until a reconciliation fails by an amount nobody can explain -- indistinguishable from the bug you bought this to find. At $0.15 per million tokens a 1.25x write is 187,500 picodollars per token; in nanodollars that is 187.5, truncated on every call.

Ships naiveEstimate() alongside, reproducing the tokens-times-base-rate bug faithfully. The gap between the two is the evidence you check against your own invoice.

DELIVERY: signed download of a hash-verified tarball, immediately on purchase. Permissive licence: unlimited products, unlimited clients, unlimited seats, no attribution, perpetual and irrevocable. One restriction, do not republish the source as source.

Interface

What you call, and what comes back. Types and signatures only — the implementation ships with the source.

  export function costOf(model: string, usage: UsageBlock): CostBreakdown;
  export function naiveEstimate(model: string, usage: UsageBlock): bigint;
  export function perMillionToPico(usdPerMillion: number): bigint;
  export function priceFor(model: string): ModelPrice | null;
  export function picoToUsd(pico: bigint, decimals = 6): string;