Budget Guards First

"STOP before exceeding $X. Not alert after."

The Problem

Your agent calls the model in a loop. 10 iterations × $0.38/call = $3.80 for a single command.

No budget alert. No circuit breaker. Credits run out. You're surprised.

AWS has billing alerts. Your agent has nothing.

The Guard Decision Flow

Agent (loop iteration)

↓ check(estimatedCost)

Sayay Guard compares usage vs budget

↓ <80%

ALLOW
proceed normally

↓ 80-95%

WARN
continue + log

↓ 95-100%

DEGRADE
use cheaper model

↓ >100%

BLOCK
stop execution

Try It: Threshold Simulator

Drag the slider to see what action triggers at each usage level:

80%

95%

ALLOW 72% of daily budget used

DIY: 60 Lines

The core interface is dead simple:

minimal-guard.ts

interface Guard { 
  check(userId: string, estimatedCost: number): Action;
  record(userId: string, actualCost: number): void;
  getUsage(userId: string): Usage;
}

type Action = 'allow' | 'warn' | 'degrade' | 'block';

interface Budget { 
  dailyUsd: number;    // e.g. 5.00
  monthlyUsd?: number; // e.g. 100.00
}

interface Thresholds { 
  warn: number;     // 0.80 (80%)
  degrade: number;  // 0.95 (95%)
}

// Storage: Map in memory, KV, Redis, or Firestore
// Reset: daily at midnight UTC
// Degrade action: switch to cheaper model (Haiku instead of Sonnet)

Or use Sayay (308 lines, zero deps, production-ready):

install

npm i @carloscortezcloud/sayay-guard

usage

import { SayayGuard, MemoryStorage } from 'sayay';

const guard = new SayayGuard({ 
  storage: new MemoryStorage(),
  budget: { dailyUsd: 5.0, monthlyUsd: 100.0 },
  thresholds: { warn: 0.8, degrade: 0.95 }
});

// Before each LLM call:
const action = guard.check(userId, estimatedCost);
if (action === 'block') throw new Error('Budget exceeded');
if (action === 'degrade') model = 'haiku'; // cheaper

// After each LLM call:
guard.record(userId, actualCost);

Key Insight

"Degrade" is the killer feature. Not block. Not warn.

When budget hits 95%, automatically switch to a cheaper model. The user barely notices (Haiku is 90% as good as Sonnet for most tasks). But you save 12x on tokens.

It's the equivalent of spot instances for compute — same work, fraction of the cost.

Sayay on GitHub → Next: Route by Complexity →