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The hot-path constraint

SaaS billing can be hours behind. A monthly invoice, reconciled later, is fine when humans drive the system. Agent billing lives in the hot path. Before every tool call, an agent needs to know:
  • How much credit is left?
  • Does this plan allow this action?
  • What’s the daily limit?
  • Is the price quote still valid?
In under 50 ms, every call. Teams keep building this stack in-house to bridge the gap. OneShot ships it out of the box.

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What OneShot provides

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Latency budget

The 50 ms target sets the ceiling for everything in the request path: Quotes are issued ahead of the call, validated on use, and removed from the cache once consumed. Balance checks are atomic single-statement updates, guarded so the check and the debit can’t disagree. Settlement happens on Base after the call returns; the agent never blocks on chain confirmation.

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Why this is hard to build

Each piece is straightforward in isolation. The trouble is the seams:
  • Hold/refund races. Two parallel tool calls reserving against the same budget. Without an atomic guard, you double-book and over-spend a daily limit.
  • Period-rollover edge cases. A subscription renews at 00:00 UTC, the renewal job fires at 00:05, but the agent calls a tool at 00:02. Was that period 1 or period 2? Idempotent renewals + a stable period-end check on every tool call answer it.
  • Subscription state divergence. Stripe says active, your DB says expired (webhook lost). On-chain says paid, your DB says pending (block reorg). Both need a reconciliation step that doesn’t double-credit.
  • Receipt taxonomy. “Spent $47 last week” is useless without categorization. Tagging at write time (instead of an offline analytics job) keeps the rollups fast and consistent.
OneShot has answered each of these in production. You don’t have to.

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When to use OneShot

Use OneShot when:
  • Your agents call tools tens of times per task.
  • You need per-call budgets, daily limits, or per-tool spend visibility.
  • You ship to multiple agent frameworks (LangChain, Virtuals, MCP) and want one billing surface.
  • You want to settle in USDC on Base without writing the EIP-712 + x402 plumbing yourself.
Stick with Stripe (or a SaaS billing stack) when:
  • Your agent only makes a handful of paid calls per session.
  • Monthly invoicing fits the customer relationship.
  • You don’t need crypto rails.
If you fall in the first bucket, the in-house build is real work: credit ledger, quote cache, renewal jobs, subscription state machine, settlement, analytics. It tends to grow legs. The infra is there if you want it.