How to Set a Budget Cap on an AI Agent

Telling an agent "don't spend more than $50" in the system prompt is not a budget cap — it is a suggestion the model can ignore, misread, or be tricked into overriding. A real cap is enforced before money moves, on every call.

This how-to shows the Naïve pattern: agent-profile budget plus Account Kit defaults. For the full governance story, read spend caps, approvals, and revocation.

Step 1 — Scope to one tenant user

Budget caps attach to an agent identity. Create or resolve the tenant user first:

const user = await naive.users.create({ email: "customer@acme.com" });
const scoped = naive.forUser(user.id);

Step 2 — Set card defaults on the Account Kit

Put the per-card ceiling in the kit's primitives_config.cards defaults:

await naive.accountKits.update(kitId, {
  primitives_config: {
    cards: {
      enabled: true,
      spending_limit_cents: 5000, // $50.00 per card
    },
  },
});

Every card the agent issues for users on this kit inherits the limit. Prepaid gift cards support a published $150 maximum (per published docs).

Step 3 — Set the agent-profile budget cap

The combined cost ceiling lives on the agent profile in your IaC config and is enforced at the governance gateway. Set limits.budget on the agent blueprint in naive.config.ts:

// naive.config.ts
import { defineConfig, agent, identity, skills } from "@usenaive-sdk/iac";
 
export default defineConfig({
  agents: {
    "travel-agent": agent({
      is: identity.agent(),
      can: [skills.llm, skills.search],
      limits: {
        budget: "$100/mo", // combined cap — alerts at 80%, hard-denies at cap
      },
    }),
  },
});

Apply with naive up. The cap sums every metered action (LLM, search, compute, hosted runtime, card spend) over the window and reserves atomically under a lock — an over-budget action returns 403 budget_exceeded. Use a soft cap if over-threshold spend should route to human approval instead.

Step 4 — Run a gated action and confirm enforcement

Issue a card or attempt a charge through the governed tool path. Confirm:

1. Under the cap → executes (or 202 if approval-gated)
2. Over the hard cap → budget_exceeded
3. Activity log shows the attempt under the correct tenant user

Step 5 — Layer approvals for irreversible spend

Caps limit volume; approvals gate sensitivity. Cards default to requiring approval for agent calls (per published docs) — combine both so a large spend within cap still waits for a human when policy demands it.

Where to go next

• How to give an AI agent a virtual card with a spend limit — card-specific walkthrough
• The Governed Agent Profile — full lifecycle
• Cards docs — issue, fund, transactions