# Service Worker

> Use when auditing repeat-visit performance, adding offline support, or evaluating PWA readiness for a web application.

- Skill: `thedaviddias/service-worker` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add thedaviddias/service-worker`
- Raw SKILL.md: https://api.skillmd.com/api/skills/thedaviddias/service-worker/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: thedaviddias (https://skillmd.com/u/thedaviddias)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/thedaviddias/service-worker

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# Register a service worker for caching and offline support

Service workers act as a programmable network proxy between the browser and the network. They eliminate repeated server round-trips for static assets, cut load times on repeat visits by 50–90 %, and allow the app to function at all on flaky or offline networks — which is critical for users on mobile or low-bandwidth connections.

## Quick Reference

- Register a service worker in your main JavaScript entry point
- Use an install event to pre-cache critical static assets
- Choose a caching strategy (cache-first, network-first, stale-while-revalidate) per resource type
- Implement an activate event to clean up old caches on update

## Check

Check whether a service worker is registered and whether it caches static assets, API responses, or provides an offline fallback.

## Fix

Add a service worker registration call and implement appropriate caching strategies for static assets and navigation requests.

## Explain

Explain how service workers intercept network requests and how different caching strategies trade off freshness vs. speed.

## Code Review

Review the service worker file and its registration. Flag missing install/ activate lifecycle handlers, absent cache-versioning, missing fetch handlers, and any patterns that could cause stale content to be served indefinitely.

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For full implementation details, code examples, and framework-specific guidance,
see `references/rule.md`.

Rule page: https://frontendchecklist.io/en/rules/performance/service-worker