IsMyBlogWorking.com now tests whether or not your web pages and XML feeds are cacheable.

If they are, that’s great, you get an elephant stamp. Browsers that visit your blog have the opportunity to use their local caches and make your pages reload faster. If they’re not, you might¹ be wasting bandwidth — particularly on feeds.

The cache test supports both Last-Updated (If-Modified-Since) and Etag (If-None-Match) checks. It tests your front page and your feed separately to see if they can produce a 304 Not Modified response when appropriate. It doesn’t validate or interpret Cache-Control and other caching directives, so it can’t confirm whether or not those items will be cached — it checks only that your server and blog platform support the conditional requests that are necessary for caching to work.

Is your blog cacheable? A Threshold State is. So is Donncha’s blog Holy Shmoly!, thanks to the WP-Super-Cache plugin. Ma.tt supports feed caching but not web.

¹ Browser caching of dynamic web caches sounds like a great idea, but it won’t always provide a significant benefit. It depends both on how dynamic the content is, and what your traffic patterns are. If your content is updated more frequently than your readers reload your pages — for example if your blog gets many comments — then browser caching won’t help much because cached content will usually be discarded as stale. And if your traffic consists mainly of one-off visits from search engines, or regular readers who click through many different pages in each session, caching will be of little or no benefit — it only reduces bandwidth on repeat visits to unchanged pages by the same browser.

XML feeds, on the other hand, are usually excellent candidates for caching. Feed readers tend to repeatedly request the same item at regular intervals. On many sites, feeds will account for a large percentage of bandwidth usage. Ensuring your feeds support caching can help to reduce your bandwidth costs.