# Billing Money Rules

> Use when creating or editing code under services/billing. Enforces Helpline's money-handling rules — integer cents only, seat limits, and BillingError for every violation.

- Skill: `coleam00/billing-money-rules` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add coleam00/billing-money-rules`
- Raw SKILL.md: https://api.skillmd.com/api/skills/coleam00/billing-money-rules/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: coleam00 (https://skillmd.com/u/coleam00)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/coleam00/billing-money-rules

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# Billing money rules

This skill activates when work is happening in `services/billing`. It exists so
money bugs never ship.

## The rules (load these every time)

1. **Money is integer cents.** Never a float, never dollars. Variables and
   fields end in `_cents`.
2. **Plan economics live in one place** — `_SEAT_LIMITS` and
   `_PRICE_PER_SEAT_CENTS` in `subscriptions.py`. Never hard-code a price or a
   limit anywhere else.
3. **Every money/plan violation raises `BillingError`** (HTTP 402). Never
   silently clamp seats, skip a charge, or return a partial result.
4. **Inactive subscriptions cannot be invoiced.**

## When you need the detail

For the full rationale, edge cases, and worked examples, read
[references/money-conventions.md](references/money-conventions.md). Only load it
when a change is non-trivial — the four rules above cover most edits.