# cf.vary Comes to Workers fetch: Fine-Grained Cache Control!

Hey there, it's me, Shiichan! Today I found a quiet-but-nice caching update to share with you.

## What was announced?

Over on the Cloudflare Changelog, they announced that Workers `fetch()` requests now support the `cf.vary` option. With it, you can control how Cloudflare caches an origin response that carries a `Vary` header, all on a single-subrequest basis.

The stage is the [Workers](https://developers.cloudflare.com/workers/) `fetch()` call. You just add `vary` to the `cf` option when you call it, which is nice and lightweight.

## The story so far

When a `Vary` header is present, responses are cached separately for each value of request headers like `Accept` or `Accept-Language`.

That behavior is correct, but if a header has lots of value variations, your cache can end up missing more often. And until now, there wasn't a way to tune this per fetch.

## What changes

By passing `cf.vary` to `fetch()`, you get to decide how `Vary` is handled for that subrequest. For each header you can choose to let it pass through or to normalize its values, so you can deliberately shrink the cache-key variations. Fewer variations means it's easier to lift your cache hit rate.

## Dive Deep

Here's what it looks like. You set the overall behavior with `default`, then override per header with `headers`.

```js
export default {
  async fetch(request) {
    return fetch(request, {
      cf: {
        vary: {
          default: { action: "bypass" },
          headers: {
            accept: {
              action: "normalize",
              media_types: ["text/html", "application/json"],
            },
            "accept-language": {
              action: "normalize",
              languages: ["en", "fr", "de"],
            },
          },
        },
      },
    });
  },
};
```

Two things to notice: setting `default.action` to `bypass` so `Vary` is passed through by default, while individually normalizing `accept` down to specific `media_types` and `accept-language` to the target `languages`.

For the full spec, check out the [cf.vary property](https://developers.cloudflare.com/workers/runtime-apis/request/#the-cfvary-property) docs.

## Wrap-up

- Workers `fetch()` now supports the `cf.vary` option
- Control how an origin `Vary` header affects caching, per subrequest
- Choose `bypass` or `normalize` for each header
- Great for shrinking value variations and tuning cache hit rates

If you've wrestled with `Vary` in multilingual or content-negotiation setups, or you want to squeeze out more cache efficiency, this one is for you!