express-metrics-middleware

0.1.14 verified Sat Apr 25 auth: no javascript

Express middleware that automatically collects standard Prometheus metrics (HTTP request duration, request count, active connections, etc.) for Node.js applications. Version 0.1.14 is the current stable release, updated infrequently. Compared to prom-client or express-prom-bundle, this package offers a zero-configuration setup with sensible defaults and built-in TypeScript types. It is opinionated and designed for quick integration without manual metric definition, but may have limited customization options.

Common errors

error TypeError: createMiddleware is not a function ↓

cause Using default import instead of named import.

fix

Use import { createMiddleware } from 'express-metrics-middleware'

error Cannot find module 'prom-client' or its corresponding type declarations. ↓

cause Missing peer dependency prom-client.

fix

Run npm install prom-client

error Metrics endpoint returns 404 ↓

cause Middleware not registered or route conflict.

fix

Ensure app.use(createMiddleware()) is called before other routes.

Warnings

gotcha The middleware exposes a /metrics endpoint by default; ensure it does not conflict with your routes or middleware order (place it before authentication if metrics should be public). ↓

fix Route /metrics explicitly with your own handler if you need custom behavior.

breaking In version 0.1.0, the function was named 'metricsMiddleware' and exported as default. In 0.1.1+ it changed to named export 'createMiddleware'. ↓

fix Use import { createMiddleware } from 'express-metrics-middleware' instead.

gotcha The middleware relies on prom-client's default metrics (collectDefaultMetrics) which may increase memory usage in long-lived processes. Disable if not needed via options. ↓

fix Pass { collectDefaultMetrics: false } to createMiddleware.

Install

npm install express-metrics-middleware

yarn add express-metrics-middleware

pnpm add express-metrics-middleware

Imports

createMiddleware

wrong

import createMiddleware from 'express-metrics-middleware'

correct

import { createMiddleware } from 'express-metrics-middleware'

Named export, not default. TypeScript types are included.

MetricsConfig

import type { MetricsConfig } from 'express-metrics-middleware'

TypeScript only; use import type for type-only import.

createMiddleware (require)

wrong

const createMiddleware = require('express-metrics-middleware')

correct

const { createMiddleware } = require('express-metrics-middleware')

CommonJS: destructure the require because it's a named export.

Quickstart

Shows how to create an Express server with the middleware that collects Prometheus metrics automatically.

import express from 'express';
import { createMiddleware } from 'express-metrics-middleware';
const app = express();
app.use(createMiddleware({ metricPrefix: 'my_app' }));
app.get('/hello', (req, res) => {
  res.send('hello world');
});
app.listen(3000, () => {
  console.log('Server running on port 3000');
});
// Metrics endpoint is automatically exposed at /metrics by default