Usage-based billing playbook

A usage-based billing playbook for apps that charge per call, per token, per document or per minute. Most AI-built apps resell model calls, so every customer action has a cost you pay at once and a price you bill later. This playbook keeps those two in step.

It covers metering, credits and prepaid balances, margins against model cost, spend caps and alerts, and usage on invoices. The last chapter covers the young protocols that let AI agents pay. Those rules are all Optional, because the protocols still change every few months.

Start with Metering. A usage event counted twice or lost is a billing bug that no invoice can fix later. Then read Margins and model cost before you set a price.

Some topics have their home elsewhere. Checkout, subscriptions, tax and invoice fields live in the payments playbook. Pricing each model call inside the app lives in Price every call and cap the spend. This playbook takes that cost and turns it into a fair bill.

Chapters

1. Metering

   Record each billable use once, on the server, as a raw event with its own key. Derive totals from the events, accept late ones up to a cut-off, then close.

   • Required 1
   • Recommended 4

2. Credits and prepaid balances

   Keep credits as ledger rows and hold them before costly work. Spend grants in a fixed order, and decide in writing what a zero balance does.

   • Required 2
   • Recommended 2
   • Avoid 1

3. Margins and model cost

   Charge each model call to the customer who caused it and keep every price above its cost with a test. Recheck margins when model prices change.

   • Required 1
   • Recommended 3

4. Spend caps and alerts

   Let customers set a hard cap on their spend and warn them before they reach it. Split caps by key or member, and show usage that matches the invoice.

   • Required 1
   • Recommended 3

5. Usage on invoices

   Put every metered charge on its own invoice line with quantity, unit price and period, and let customers download the events behind each line.

   • Required 1
   • Recommended 2

6. Agentic payments

   Protocols that let AI agents pay are young and change often. Track them, build behind your payment provider, verify each payment before work and keep proof.

   • Optional 4

All 25 rules on one page

This is a lot to check. An Expert can check it for you.

Related playbooks

• Latency, cost and fallbacks

  In the AI features playbook. Every bill starts with the cost of one model call. Price each call and cap it inside the app first.

• Subscriptions

  In the Payments and billing playbook. Most usage plans sit on a subscription. Let the provider run renewals, consent and cancelling.

• Transactions and concurrency

  In the Data and databases playbook. Credits and usage counts break under parallel requests. Transactions and conditional writes keep them right.

• AI agents and models

  In the Adversarial testing playbook. A runaway agent burns credits in minutes. Test the limits on cost, steps and loops.