Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx agentmods add rules/nikandr-surkov/ai-saas-starter/billinggit clone --depth 1 https://github.com/nikandr-surkov/ai-saas-starterWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/rules/nikandr-surkov/ai-saas-starter/billing)<a href="https://agentmods.dev/rules/nikandr-surkov/ai-saas-starter/billing"><img src="https://agentmods.dev/badge/rules/nikandr-surkov/ai-saas-starter/billing.svg" alt="Measured on agentmods" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5 | $0.00000 | $0.00232 |
| Opus 5 | $0.00000 | $0.00116 |
| Sonnet 5 | $0.00000 | $0.00046 |
| Haiku 4.5 | $0.00000 | $0.00023 |
Grade A, and why
billing scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 5d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
What it actually says
- Every credit mutation carries an
idempotencyKey. Unique-violation on it means "already processed" — return the existing row silently. syncStripeDataToDb(customerId)insrc/lib/billing/sync.tsis the ONLY code that writes subscription state. It fetches fresh from Stripe; event payloads are triggers, not sources of truth.- The ledger is append-only: no UPDATE/DELETE on
credit_transactions. Corrections are new compensating rows. - Spends: single conditional UPDATE (
credit_balance >= amountin WHERE) in the same transaction as the ledger insert. No check-then-write. - Webhook: verify the Stripe signature on the RAW body (
request.text()) before anything else. 200 fast; 500 on real failures so Stripe retries. - Test subscription lifecycles with Stripe test clocks.
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 5d ago First seen · 22 lines · 0 tokens per session scan A 5b4278499f5f
billing is a cursor rule published in the GitHub repository nikandr-surkov/ai-saas-starter (16 stars, last pushed 1mo ago), licensed MIT. It costs nothing until one of its globs matches a file; then it loads 232 tokens. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
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┌─────────────────┐ ┌──────────────────┐ ┌─────────────────┐ │ Wallet Provider│ │ Connection Mgmt │ │ Transaction Svc │ │ - Private Keys │───▶│ - RPC Endpoints │───▶│ - Tx Construction│ │ - Public Keys │ │ - Network Config │ │ - Fee Estimation│ │ - Signatures │ │ - Health Check │ │ - Broadcasting │ └─────────────────┘…