Undici Has a Free API — Here's How to Use Node.js's Fastest HTTP Client

Undici is the HTTP/1.1 client that powers Node.js's built-in fetch. It is significantly faster than the legacy http module and provides connection pooling, interceptors, and streaming.

Installation

npm install undici

Note: Undici is bundled with Node.js 18+ as the engine behind globalThis.fetch.

Basic Requests

import { request } from "undici";

// Simple GET
const { statusCode, headers, body } = await request("https://api.github.com/users/nodejs", {
  headers: { "User-Agent": "undici-example" }
});
const data = await body.json();
console.log(`${data.login}: ${data.public_repos} repos`);

Connection Pooling

import { Pool } from "undici";

// Create a pool with 10 connections
const pool = new Pool("https://api.example.com", {
  connections: 10,
  pipelining: 1
});

// Make concurrent requests through the pool
const results = await Promise.all(
  Array.from({ length: 100 }, (_, i) =>
    pool.request({ path: `/items/${i}`, method: "GET" })
      .then(({ body }) => body.json())
  )
);
console.log(`Fetched ${results.length} items`);

await pool.close();

Interceptors

import { Agent, setGlobalDispatcher } from "undici";

const agent = new Agent().compose([
  (dispatch) => (opts, handler) => {
    opts.headers = {
      ...opts.headers,
      "Authorization": "Bearer my-token"
    };
    return dispatch(opts, handler);
  }
]);

setGlobalDispatcher(agent);

// All requests now include the auth header
const { body } = await request("https://api.example.com/me");

Streaming Downloads

import { stream } from "undici";
import { createWriteStream } from "node:fs";

await stream("https://example.com/large-file.zip", { method: "GET" }, () => {
  return createWriteStream("output.zip");
});

MockAgent for Testing

import { MockAgent, setGlobalDispatcher } from "undici";

const mockAgent = new MockAgent();
setGlobalDispatcher(mockAgent);

const mockPool = mockAgent.get("https://api.example.com");
mockPool.intercept({ path: "/users/1", method: "GET" }).reply(200, {
  id: 1, name: "Test User"
});

// This now returns the mocked response
const { body } = await request("https://api.example.com/users/1");
console.log(await body.json()); // { id: 1, name: "Test User" }

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