output-dev-cost-hooks

Cost Observability Hooks

Overview

This skill documents how to subscribe to Output's cost events so every priced LLM call and every HTTP call with attached cost (via addRequestCost, see output-dev-http-client-create) can be forwarded to your own observability system — a webhook, a structured log pipeline, a metrics backend, etc. Handler errors are caught and logged by the framework; they never affect the workflow or the request that triggered them.

When to Use This Skill

• Forwarding per-call spend to an external observability/webhook endpoint
• Logging cost events as structured fields for a log platform
• Building alerting or dashboards on top of workflow spend
• Auditing which workflows/activities are driving cost, in real time rather than after the fact

This skill is about project-wide hook registration for cost data already emitted by the framework. To make an HTTP client emit cost in the first place, see output-dev-http-client-create.

Setup

1. Create a hook file

// src/cost_hooks.ts
import { on } from '@outputai/core/hooks';
import type { HttpRequestCostEvent } from '@outputai/core/http';
import type { LLMGenerationMeteringEvent } from '@outputai/llm';

on<HttpRequestCostEvent>('cost:http:request', async event => {
  // handle HTTP cost
});

on<LLMGenerationMeteringEvent>('llm:generation:metering', async event => {
  // handle LLM cost
});

2. Register the file

Add the file to outputai.hookFiles in package.json, alongside any existing hook files. Paths are relative to the package root and point at the built .js output — npm run output:worker:build compiles src/ to dist/ (per tsconfig.json's rootDir/outDir), so src/cost_hooks.ts is registered as dist/cost_hooks.js, not the .ts source itself. The worker loads these files at startup.

{
  "outputai": {
    "hookFiles": [
      "./dist/cost_hooks.js"
    ]
  }
}

If you'd rather skip the build step, a hook file can also be plain, uncompiled JavaScript registered directly at its src/ path ("./src/cost_hooks.js") — see https://docs.output.ai/operations/error-hooks for that variant. The rest of this skill uses TypeScript + the built-output path, since that's what the framework's own examples (and every other file in a scaffolded project) use.