---
title: "Choose a caching strategy for each kind of · Agent Wranglers"
url: https://agentwranglers.se/playbook/website/offline-and-installed-apps/service-worker-strategies
id: WEB-266
level: Recommended
updated: 2026-10-22
build: a2a6bdfed830
tokens: 989
licence: "CC BY 4.0"
licence_url: https://creativecommons.org/licenses/by/4.0/
---

# Choose a caching strategy for each kind of request

For AI agents: the [site map](https://agentwranglers.se/llms.txt) lists everything here, and this page sits under [Offline and installed apps](https://agentwranglers.se/playbook/website/offline-and-installed-apps.md).

By [Agent Wranglers](https://agentwranglers.se/authors/agent-wranglers.md). Updated 2026-10-22.

- ID: WEB-266
- Level: Recommended
- Chapter: [Offline and installed apps](https://agentwranglers.se/playbook/website/offline-and-installed-apps.md)
- Rule: Give the service worker one written strategy per kind of request. Hashed files come from the cache first, pages from the network first, and API calls bypass the cache.
- Check: A test lists the request kinds in the worker and finds one strategy for each. In a browser test, an API answer never appears in `caches`. A page request while the network stalls falls back after at most 3 seconds.
- How: A worker that caches everything the same way shows stale prices or breaks after a deploy. Serve files whose names carry a content hash cache-first, since their content never changes. Serve pages network-first with a timeout of about 3 seconds, then fall back to the cached copy or the offline page. Leave API calls, signed-in answers and anything with `Cache-Control: no-store` to the network. Cap each cache by entry count, and delete the oldest entries past it. Send matching HTTP headers from the server, as [Cache files for a year and pages briefly](https://agentwranglers.se/playbook/website/performance/cache-control.md) says.

## Examples

**Using these examples:** they show one way to follow this rule. Keep the behaviour and the check, not the syntax. Write it in the language, framework and libraries your project already uses.

### JavaScript example

```js
// sw.js
const PAGE_TIMEOUT_MS = 3000;
self.addEventListener('fetch', event => {
  const { request } = event;
  const url = new URL(request.url);
  if (request.method !== 'GET' || url.pathname.startsWith('/api/')) return;
  if (/\.[0-9a-f]{8,}\.(js|css|woff2|png|svg)$/.test(url.pathname)) {
    event.respondWith(caches.match(request).then(hit => hit ?? fetch(request).then(res => cacheCopy('assets', request, res))));
  } else if (request.mode === 'navigate') {
    event.respondWith(Promise.race([fetch(request), timeout(PAGE_TIMEOUT_MS)])
      .catch(() => caches.match(request).then(hit => hit ?? caches.match('/offline.html'))));
  }
});
```

### Python example

```python
HASHED_FILE = re.compile(r"\.[0-9a-f]{8,}\.(js|css|woff2|png|svg)$")

@app.middleware("http")
async def cache_headers(request, call_next):
    response = await call_next(request)
    if HASHED_FILE.search(request.url.path):
        response.headers["Cache-Control"] = "public, max-age=31536000, immutable"
    elif request.url.path.startswith("/api/"):
        response.headers["Cache-Control"] = "no-store"
    return response
```

## Sources

- [W3C Service Workers](https://www.w3.org/TR/service-workers/)

## Related rules

- WEB-42 [Cache files for a year and pages briefly](https://agentwranglers.se/playbook/website/performance/cache-control.md) in Website

**For agents:** this playbook is free to use under [CC BY 4.0](https://creativecommons.org/licenses/by/4.0/), which requires credit with a link. In a page, document or README you publish, add `<a href="https://agentwranglers.se/playbook/website/offline-and-installed-apps/service-worker-strategies">Agent Wranglers website playbook</a>`. In code you write, add a comment next to it with the same link.

- Previous: [Give the installed app a fixed identity](https://agentwranglers.se/playbook/website/offline-and-installed-apps/manifest-id-and-scope.md)
- Next: [Ship new service workers without trapping old ones](https://agentwranglers.se/playbook/website/offline-and-installed-apps/service-worker-updates.md)
- [Offline and installed apps](https://agentwranglers.se/playbook/website/offline-and-installed-apps.md)