Express

Setup

Create an instrumentation.ts file:

instrumentation.ts

import 'autotel/register'; // Must be first for ESM

import { init } from 'autotel';
import pino from 'pino';

const logger = pino({ name: 'my-api' });

init({
  service: 'my-api',
  logger,
  autoInstrumentations: ['express', 'http', 'pino'],
  endpoint: process.env.OTLP_ENDPOINT,
});

Run with the --import flag:

tsx --import ./instrumentation.ts src/index.ts

Tracing Route Handlers

import express from 'express';
import { trace, type TraceContext } from 'autotel';

const app = express();

// Auto-traced: HTTP spans created by auto-instrumentation
// Manual trace: business logic spans
const fetchUser = trace((ctx: TraceContext) => async (userId: string) => {
  ctx.setAttribute('db.userId', userId);
  return await db.users.findById(userId);
});

app.get('/users/:userId', async (req, res) => {
  const user = await fetchUser(req.params.userId);
  res.json(user);
});

app.get('/error', async () => {
  throw new Error('Test error'); // Automatically captured
});

Request-Scoped Logging

import { trace, getRequestLogger } from 'autotel';

app.get('/checkout', async (req, res) => {
  // If using autotel-hono or middleware that creates a span,
  // getRequestLogger() works without ctx
  const log = getRequestLogger();

  log.set({ userId: req.body.userId });
  const result = await processCheckout(req.body);
  log.set({ orderId: result.id });
  log.emitNow(); // One wide event per request

  res.json(result);
});

What Gets Traced

With autoInstrumentations: ['express', 'http']:

• HTTP server spans — automatic per-request spans with method, path, status
• Express middleware — middleware execution time
• Your trace() calls — business logic spans as children

Examples

• example-http — Express with Pino logger, manual trace() in routes, error tracking.