Budget controls for autonomous AI agents

Autonomous AI agents can accumulate significant costs. Each API call, database query, and cloud operation has a price. Without budget controls, an agent running overnight can spend thousands of dollars. Budget controls set hard limits on what the agent can spend.

Types of budget limits

Per-action limits

Cap the cost of any single action:

- tool: "payment.send"
  action: allow
  when:
    args.amount:
      lte: 100
  reason: "Payments up to $100 are automatic"

- tool: "payment.send"
  action: escalate
  when:
    args.amount:
      lte: 1000
  reason: "Payments $100-$1000 require approval"

- tool: "payment.send"
  action: block
  reason: "Payments over $1000 are blocked"

Per-session limits

Cap the total cost within a session:

const guard = createGuard({
  policy,
  budget: {
    maxPerSession: 500.00,
    tracking: {
      'payment.send': (args) => args.amount,
      'cloud.compute': (args) => args.estimatedCost,
      'api.call': () => 0.01,  // Flat cost per call
    }
  }
});

Per-day limits

Cap the total cost across all sessions in a 24-hour period:

budget: {
  maxPerDay: 2000.00,
  maxPerSession: 500.00,
}

Per-tool limits

Different tools have different cost profiles:

budget: {
  perTool: {
    'payment.send': { maxPerDay: 1000.00 },
    'cloud.compute': { maxPerDay: 200.00 },
    'api.call': { maxPerDay: 50.00 },
  }
}

What happens when the budget is exceeded

When a budget limit is hit, the guard blocks the action:

const decision = guard('payment.send', { amount: 200, to: 'vendor' });
// decision.action === 'block'
// decision.reason === 'Session budget exceeded ($480/$500)'

For a softer approach, escalate instead of blocking:

budget: {
  maxPerSession: 500.00,
  onExceeded: 'escalate',  // Instead of 'block'
}

Token usage budgets

For agents that use LLM APIs, track token consumption:

budget: {
  maxTokensPerSession: 100_000,
  maxTokensPerDay: 1_000_000,
  tokenCost: {
    input: 0.000003,   // Per token
    output: 0.000015,  // Per token
  }
}

Alerting

Set alert thresholds below the hard limit:

budget: {
  maxPerSession: 500.00,
  alertAt: 0.8,  // Alert at 80% ($400)
  onAlert: (usage) => {
    notify('budget-alert', {
      used: usage.amount,
      limit: usage.limit,
      session: usage.sessionId,
    });
  }
}

This gives operators time to review the agent's spending before it hits the hard limit.

Why budget controls are critical

An agent with access to payment tools and no budget controls is a liability. A single prompt injection or hallucinated action can trigger a large unauthorized payment. Budget controls are the financial equivalent of rate limiting: they bound the maximum damage from any failure mode.