undici

Undici is an open-source HTTP client library for Node.js that is designed to deliver high performance for outbound requests. It emphasizes low overhead, efficient connection management, and streaming capabilities, making it well-suited for high-throughput applications and services that rely on external HTTP calls.

The library provides a low-level API centered on two main abstractions: Pool and Client. A Pool manages a pool of persistent connections to a single origin, enabling efficient reuse of connections for multiple requests. A Client offers direct control over individual requests. Requests and responses are handled asynchronously, with support for streaming request bodies and response data, which helps minimize memory usage for large payloads.

Key features include connection pooling, keep-alive connections, and a design focused on performance in the Node.js environment. Undici aims to outperform the built-in HTTP modules by reducing overhead and improving throughput on typical workloads. It adheres to standard HTTP/1.1 semantics and provides a straightforward API for making and handling HTTP requests.

In the Node.js ecosystem, undici has influenced modern HTTP client development and is used as the underlying technology behind Node.js’s built-in fetch implementation in recent releases. The library is maintained by the open-source community and is widely adopted in production systems that require fast, scalable HTTP communication.