cache

Cache

Most of a Claude Code bill is not what people picture. Cache reads are billed at a tenth of the input rate and usually dominate the volume; cache writes carry premiums (1.25× for 5-minute, 2× for 1-hour entries). This skill answers "why is my bill like this" from the metered ledger. The engine computes every number; you write the prose around them and never adjust a figure.

"${CLAUDE_PLUGIN_ROOT}/bin/waybill" mine --all    # catch-up metering first, always
"${CLAUDE_PLUGIN_ROOT}/bin/waybill" query cache [--from <date>] [--to <date>]

The payload (data):

• tokens — volume by class: input, output, cache_read, cache_creation (with the 5m/1h write split); cache_read_pct is reads as a share of total volume.
• by_model — the same per model, each with a derived effective_usd (null when no rate resolves — never $0).
• billed — the cost view, derived from the current rate table and labeled so (basis: "list_price_equivalent_derived"): effective_usd (the tokens priced as billed), list_equivalent_usd (the same tokens with no caching at all), saved_usd (the NET saving, write premiums already paid for), cache_read_share_of_billed_pct, and covered_pct (how much of the volume the dollar math covers).
• unattributed_pct — the honesty floor; it travels on every payload.

Rendering rules

Honor the detail axis (config detail_default, --detail override):

• terse (1–3 lines): total volume, the cache-read share, and the net saving with its basis label. Even at terse, never drop the unattributed %, covered_pct when below 100, or the derived-basis label — those survive every level.
• standard: the above plus the tier table (input / output / reads / 5m writes / 1h writes) and the effective-vs-list pair.
• full: everything, including per-model rows.

Language rules (methodology): "saved" is always derived, list-price equivalent — say so; it is not a stored fact and not a promise about the actual invoice. When covered_pct < 100, name the unpriced models (waybill status lists them with fixes) rather than presenting a partial dollar figure as complete. Ranges stay ranges; the unattributed share is shown, never hidden.