# Service Workers
Confidence: high
Last verified: 2026-05-22
Generation: human_only


## TL;DR

Service Workers are programmable network proxies that run in the browser background, intercepting network requests to enable offline functionality, push notifications, and background sync. They are the foundation of Progressive Web Apps (PWAs).

## Core Explanation

Service Workers run on a separate thread, have no DOM access, and are event-driven (`fetch`, `install`, `activate`). They have a finite lifetime — the browser may terminate and restart them. Key capabilities: caching strategies (Cache API), offline fallback, background sync (`sync` event), and push notifications. Service workers require HTTPS (except localhost).

## Further Reading

- [Service Workers Nightly (W3C)](https://w3c.github.io/ServiceWorker/)