OpenMetrics-Compatible Metrics Library

A production-ready, type-safe implementation of OpenMetrics standard for Node.js / Deno / Bun applications with zero dependencies.

Features

• 100% OpenMetrics Compliance - Fully implements OpenMetrics specification with proper content-type headers
• TypeScript First - Complete type definitions and generics support
• Comprehensive Metric Types:
  • 🔢 Counters - Monotonically increasing values
  • 📊 Gauges - Arbitrary up/down values
  • ⏱️ Histograms - Bucketed observations with configurable buckets
  • 📈 Summaries - Sliding window quantiles
  • ℹ️ Info - Static metadata (always value=1)
  • 🗂️ StateSets - Mutually exclusive states (like enums)
  • ❓ Unknown - Special cases (use sparingly)
• Automatic Registry Management - Optional auto-registration
• Label Support - Multi-dimensional metrics with proper escaping
• Time-Based Windowing - Configurable observation windows for summaries

Installation

npm install @rabbit-company/openmetrics-client
# or
yarn add @rabbit-company/openmetrics-client

Quick Start

import { Registry, Counter, Gauge, Histogram } from "@rabbit-company/openmetrics-client";

// 1. Create registry (singleton recommended)
const registry = new Registry({
	prefix: "myapp", // Optional metric prefix
});

// 2. Define metrics
const httpRequests = new Counter({
	name: "http_requests_total",
	help: "Total HTTP requests",
	labelNames: ["method", "status"],
	registry,
});

const tempGauge = new Gauge({
	name: "temperature_celsius",
	help: "Current temperature",
	unit: "celsius",
	labelNames: ["location"],
	registry,
});

// 3. Record metrics
httpRequests.labels({ method: "GET", status: "200" }).inc();
tempGauge.labels({ location: "server_room" }).set(23.5);

// 4. Expose metrics endpoint
import express from "express";
const app = express();

app.get("/metrics", (req, res) => {
	res.set("Content-Type", Registry.contentType).send(registry.metricsText());
});

app.listen(8080);

Metric Types Guide

📈 Counter (monotonically increasing)

const counter = new Counter({
	name: "login_attempts_total",
	help: "Total user login attempts",
	labelNames: ["result"], // Optional labels
	registry,
});

// Usage:
counter.labels({ result: "success" }).inc(); // +1
counter.labels({ result: "success" }).inc(5); // +5

🔢 Gauge (arbitrary values)

const gauge = new Gauge({
	name: "memory_usage_bytes",
	help: "Current memory usage",
	unit: "bytes", // Recommended for units
	registry,
});

// Usage:
gauge.set(512 * 1024 * 1024); // Absolute value
gauge.inc(100); // Increase
gauge.dec(50); // Decrease

⏱️ Histogram (bucketed observations)

const histogram = new Histogram({
	name: "http_request_duration_seconds",
	help: "Request duration distribution",
	buckets: [0.1, 0.5, 1, 2.5, 5, 10], // Custom buckets
	registry,
});

// Usage:
histogram.observe(1.23); // Record duration

⚖️ GaugeHistogram (current distribution)

const requestSizes = new GaugeHistogram({
	name: "http_request_size_bytes",
	help: "Current request size distribution",
	buckets: [100, 500, 1000, 5000],
	unit: "bytes",
	registry,
});

requestSizes.observe(450); // Falls in 500 bucket
requestSizes.observe(1200); // Falls in 5000 bucket

📊 Summary (quantiles over sliding window)

const summary = new Summary({
	name: "database_query_duration",
	help: "Query performance quantiles",
	quantiles: [0.5, 0.9, 0.99], // Default quantiles
	maxAgeSeconds: 300, // 5 minute window
	ageBuckets: 5, // Number of buckets
	registry,
});

// Usage:
summary.observe(0.42);

🗂️ StateSet (mutually exclusive states)

const serviceState = new StateSet({
	name: "service_status",
	help: "Current service state",
	states: ["starting", "running", "degraded", "stopped"],
	labelNames: ["instance"], // Optional labels
	registry,
});

// Usage:
serviceState.labels({ instance: "api-1" }).enableOnly("running");

ℹ️ Info (static metadata)

const buildInfo = new Info({
	name: "build_info",
	help: "Build information",
	labelNames: ["version", "commit", "env"],
	registry,
});

buildInfo
	.labels({
		version: "1.2.3",
		commit: "abc123",
		env: process.env.NODE_ENV,
	})
	.set();

❓ Unknown (special cases)

const specialMetric = new Unknown({
	name: "custom_metric",
	help: "Special non-standard metric",
	registry,
});

specialMetric.set(42);